[PATCH v1 0/5] Reenable might_sleep() checks for might_fault()

[PATCH v1 0/5] Reenable might_sleep() checks for might_fault()

[David Hildenbrand]

I recently discovered that might_fault() doesn't call might_sleep() anymore.
Therefore bugs like:
	spin_lock(&lock);
	rc = copy_to_user(...);
	spin_unlock(&lock);
would not be detected with CONFIG_DEBUG_ATOMIC_SLEEP. The code was changed to
disable false positives for code like:
	pagefault_disable();
	rc = copy_to_user(...);
	pagefault_enable();

Until now, pagefault_disable() and pagefault_enable() simply modified the
preempt count, therefore telling the pagefault handler that the context is
atomic and sleeping is disallowed.

In order to reenable might_sleep() checks for the correct path, we need a way to
detect whether we run in a pagefault_disable() context.

This series therefore introduces a separate pagefault_count and uses it to count
the levels of pagefault_disable() per thread. might_sleep() checks are
reactivated for the !pagefault_disable() path.

So this should now work:
	spin_lock(&lock); /* also if left away */
	pagefault_disable()
	rc = copy_to_user(...);
	pagefault_enable();
	spin_unlock(&lock);
And this should report a warning again:
	spin_lock(&lock);
	rc = copy_to_user(...);
	spin_unlock(&lock);

Please note that this series will not completely split the handling of
pagefault_disable() and the preempt count. This will be done in another series.
Purpose of this series is to reenable might_sleep() checks for might_fault(),
avoiding to produce false positives.

Cross compiled on powerpc, arm, sparc, sparc64, arm64, x86_64, i386, mips,
alpha, ia64, xtensa, m68k, microblaze.

Tested on s390. Would be good to get some feedback on the ASM offsets for m32r,
sparc and xtensa (or if I should simply move the count to the end of the struct
for these archs ...).

Thanks!

David


David Hildenbrand (5):
  uaccess: add pagefault_count to thread_info
  uaccess: count pagefault_disable() levels in pagefault_count
  mm, uaccess: trigger might_sleep() in might_fault() when pagefaults
    are disabled
  uaccess: clearify that uaccess may only sleep if pagefaults are not
    disabled
  uaccess: CONFIG_DEBUG_PAGEFAULT_COUNT to debug pagefault_count

 arch/alpha/include/asm/thread_info.h      |  1 +
 arch/arc/include/asm/thread_info.h        |  1 +
 arch/arm/include/asm/thread_info.h        |  1 +
 arch/arm64/include/asm/thread_info.h      |  1 +
 arch/avr32/include/asm/thread_info.h      |  1 +
 arch/avr32/include/asm/uaccess.h          | 12 +++++---
 arch/blackfin/include/asm/thread_info.h   |  1 +
 arch/c6x/include/asm/thread_info.h        |  1 +
 arch/cris/include/asm/thread_info.h       |  1 +
 arch/frv/include/asm/thread_info.h        |  1 +
 arch/hexagon/include/asm/thread_info.h    |  1 +
 arch/hexagon/include/asm/uaccess.h        |  3 +-
 arch/ia64/include/asm/thread_info.h       |  1 +
 arch/m32r/include/asm/thread_info.h       |  5 +--
 arch/m32r/include/asm/uaccess.h           | 30 ++++++++++++------
 arch/m68k/include/asm/thread_info.h       |  1 +
 arch/metag/include/asm/thread_info.h      |  1 +
 arch/microblaze/include/asm/thread_info.h |  1 +
 arch/microblaze/include/asm/uaccess.h     |  6 ++--
 arch/mips/include/asm/thread_info.h       |  1 +
 arch/mips/include/asm/uaccess.h           | 45 ++++++++++++++++++---------
 arch/mn10300/include/asm/thread_info.h    |  1 +
 arch/openrisc/include/asm/thread_info.h   |  1 +
 arch/parisc/include/asm/thread_info.h     |  1 +
 arch/powerpc/include/asm/thread_info.h    |  1 +
 arch/s390/include/asm/thread_info.h       |  1 +
 arch/s390/include/asm/uaccess.h           | 15 ++++++---
 arch/score/include/asm/thread_info.h      |  1 +
 arch/score/include/asm/uaccess.h          | 15 ++++++---
 arch/sh/include/asm/thread_info.h         |  1 +
 arch/sparc/include/asm/thread_info_32.h   | 20 ++++++------
 arch/sparc/include/asm/thread_info_64.h   | 17 ++++++-----
 arch/tile/include/asm/thread_info.h       |  1 +
 arch/tile/include/asm/uaccess.h           | 21 ++++++++-----
 arch/um/include/asm/thread_info.h         |  1 +
 arch/unicore32/include/asm/thread_info.h  |  1 +
 arch/x86/include/asm/thread_info.h        |  1 +
 arch/x86/include/asm/uaccess.h            | 15 ++++++---
 arch/x86/include/asm/uaccess_32.h         |  6 ++--
 arch/x86/lib/usercopy_32.c                |  6 ++--
 arch/xtensa/include/asm/thread_info.h     |  5 +--
 include/linux/kernel.h                    |  3 +-
 include/linux/uaccess.h                   | 51 ++++++++++++++++++++++++++-----
 lib/Kconfig.debug                         |  9 ++++++
 lib/strnlen_user.c                        |  6 ++--
 mm/maccess.c                              | 11 +++++++
 mm/memory.c                               | 19 +++++-------
 47 files changed, 245 insertions(+), 101 deletions(-)

-- 
1.8.5.5

[PATCH v1 1/5] uaccess: add pagefault_count to thread_info

[David Hildenbrand]

This patch adds the pagefault_count to the thread_info of all
architectures. It will be used to count the pagefault_disable() levels
on a per-thread basis.

We are not reusing the preempt_count as this is per cpu on x86 and we want to
demangle pagefault_disable() from preemption in the future.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
---
 arch/alpha/include/asm/thread_info.h      |  1 +
 arch/arc/include/asm/thread_info.h        |  1 +
 arch/arm/include/asm/thread_info.h        |  1 +
 arch/arm64/include/asm/thread_info.h      |  1 +
 arch/avr32/include/asm/thread_info.h      |  1 +
 arch/blackfin/include/asm/thread_info.h   |  1 +
 arch/c6x/include/asm/thread_info.h        |  1 +
 arch/cris/include/asm/thread_info.h       |  1 +
 arch/frv/include/asm/thread_info.h        |  1 +
 arch/hexagon/include/asm/thread_info.h    |  1 +
 arch/ia64/include/asm/thread_info.h       |  1 +
 arch/m32r/include/asm/thread_info.h       |  5 +++--
 arch/m68k/include/asm/thread_info.h       |  1 +
 arch/metag/include/asm/thread_info.h      |  1 +
 arch/microblaze/include/asm/thread_info.h |  1 +
 arch/mips/include/asm/thread_info.h       |  1 +
 arch/mn10300/include/asm/thread_info.h    |  1 +
 arch/openrisc/include/asm/thread_info.h   |  1 +
 arch/parisc/include/asm/thread_info.h     |  1 +
 arch/powerpc/include/asm/thread_info.h    |  1 +
 arch/s390/include/asm/thread_info.h       |  1 +
 arch/score/include/asm/thread_info.h      |  1 +
 arch/sh/include/asm/thread_info.h         |  1 +
 arch/sparc/include/asm/thread_info_32.h   | 20 +++++++++++---------
 arch/sparc/include/asm/thread_info_64.h   | 17 +++++++++--------
 arch/tile/include/asm/thread_info.h       |  1 +
 arch/um/include/asm/thread_info.h         |  1 +
 arch/unicore32/include/asm/thread_info.h  |  1 +
 arch/x86/include/asm/thread_info.h        |  1 +
 arch/xtensa/include/asm/thread_info.h     |  5 +++--
 30 files changed, 52 insertions(+), 21 deletions(-)

diff --git a/arch/alpha/include/asm/thread_info.h b/arch/alpha/include/asm/thread_info.h
index 48bbea6..1830671 100644
--- a/arch/alpha/include/asm/thread_info.h
+++ b/arch/alpha/include/asm/thread_info.h
@@ -22,6 +22,7 @@ struct thread_info {
 	mm_segment_t		addr_limit;	/* thread address space */
 	unsigned		cpu;		/* current CPU */
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 	unsigned int		status;		/* thread-synchronous flags */
 
 	int bpt_nsaved;
diff --git a/arch/arc/include/asm/thread_info.h b/arch/arc/include/asm/thread_info.h
index 02bc5ec..2fde704 100644
--- a/arch/arc/include/asm/thread_info.h
+++ b/arch/arc/include/asm/thread_info.h
@@ -41,6 +41,7 @@
 struct thread_info {
 	unsigned long flags;		/* low level flags */
 	int preempt_count;		/* 0 => preemptable, <0 => BUG */
+	int pagefault_count;		/* pagefault_disable() levels */
 	struct task_struct *task;	/* main task structure */
 	mm_segment_t addr_limit;	/* thread address space */
 	struct exec_domain *exec_domain;/* execution domain */
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index ce73ab6..bf47d2d 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -51,6 +51,7 @@ struct cpu_context_save {
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			pagefault_count;/* pagefault_disable() levels */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain	*exec_domain;	/* execution domain */
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 459bf8e..2469f15 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -50,6 +50,7 @@ struct thread_info {
 	struct exec_domain	*exec_domain;	/* execution domain */
 	struct restart_block	restart_block;
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
+	int			pagefault_count;/* pagefault_disable() levels */
 	int			cpu;		/* cpu */
 };
 
diff --git a/arch/avr32/include/asm/thread_info.h b/arch/avr32/include/asm/thread_info.h
index a978f3f..0c1d6f7 100644
--- a/arch/avr32/include/asm/thread_info.h
+++ b/arch/avr32/include/asm/thread_info.h
@@ -25,6 +25,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	__s32			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	__s32			pagefault_count;/* pagefault_disable() levels */
 	__u32			rar_saved;	/* return address... */
 	__u32			rsr_saved;	/* ...and status register
 						   saved by debug handler
diff --git a/arch/blackfin/include/asm/thread_info.h b/arch/blackfin/include/asm/thread_info.h
index 55f473b..3ba26aa 100644
--- a/arch/blackfin/include/asm/thread_info.h
+++ b/arch/blackfin/include/asm/thread_info.h
@@ -41,6 +41,7 @@ struct thread_info {
 	unsigned long flags;	/* low level flags */
 	int cpu;		/* cpu we're on */
 	int preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int pagefault_count;	/* pagefault_disable() levels */
 	mm_segment_t addr_limit;	/* address limit */
 	struct restart_block restart_block;
 #ifndef CONFIG_SMP
diff --git a/arch/c6x/include/asm/thread_info.h b/arch/c6x/include/asm/thread_info.h
index d4e9ef8..6b2dcac 100644
--- a/arch/c6x/include/asm/thread_info.h
+++ b/arch/c6x/include/asm/thread_info.h
@@ -44,6 +44,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 = preemptable, <0 = BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block	restart_block;
 };
diff --git a/arch/cris/include/asm/thread_info.h b/arch/cris/include/asm/thread_info.h
index 55dede1..3356902 100644
--- a/arch/cris/include/asm/thread_info.h
+++ b/arch/cris/include/asm/thread_info.h
@@ -32,6 +32,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 	__u32			tls;		/* TLS for this thread */
 
 	mm_segment_t		addr_limit;	/* thread address space:
diff --git a/arch/frv/include/asm/thread_info.h b/arch/frv/include/asm/thread_info.h
index af29e17..79a97ee 100644
--- a/arch/frv/include/asm/thread_info.h
+++ b/arch/frv/include/asm/thread_info.h
@@ -36,6 +36,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 						 * 0-0xBFFFFFFF for user-thead
diff --git a/arch/hexagon/include/asm/thread_info.h b/arch/hexagon/include/asm/thread_info.h
index a59dad3..d54042e 100644
--- a/arch/hexagon/include/asm/thread_info.h
+++ b/arch/hexagon/include/asm/thread_info.h
@@ -51,6 +51,7 @@ struct thread_info {
 	unsigned long		flags;          /* low level flags */
 	__u32                   cpu;            /* current cpu */
 	int                     preempt_count;  /* 0=>preemptible,<0=>BUG */
+	int                     pagefault_count;/* pagefault_disable() levels */
 	mm_segment_t            addr_limit;     /* segmentation sux */
 	/*
 	 * used for syscalls somehow;
diff --git a/arch/ia64/include/asm/thread_info.h b/arch/ia64/include/asm/thread_info.h
index 5b17418..14f128c 100644
--- a/arch/ia64/include/asm/thread_info.h
+++ b/arch/ia64/include/asm/thread_info.h
@@ -27,6 +27,7 @@ struct thread_info {
 	__u32 status;			/* Thread synchronous flags */
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int pagefault_count;		/* pagefault_disable() levels */
 	struct restart_block restart_block;
 #ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
 	__u64 ac_stamp;
diff --git a/arch/m32r/include/asm/thread_info.h b/arch/m32r/include/asm/thread_info.h
index 0017170..a1ec910 100644
--- a/arch/m32r/include/asm/thread_info.h
+++ b/arch/m32r/include/asm/thread_info.h
@@ -29,6 +29,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user-thread
@@ -48,8 +49,8 @@ struct thread_info {
 #define TI_STATUS	0x0000000C
 #define TI_CPU		0x00000010
 #define TI_PRE_COUNT	0x00000014
-#define TI_ADDR_LIMIT	0x00000018
-#define TI_RESTART_BLOCK 0x000001C
+#define TI_ADDR_LIMIT	0x0000001C
+#define TI_RESTART_BLOCK 0x0000020
 
 #endif
 
diff --git a/arch/m68k/include/asm/thread_info.h b/arch/m68k/include/asm/thread_info.h
index 21a4784..5a6a203 100644
--- a/arch/m68k/include/asm/thread_info.h
+++ b/arch/m68k/include/asm/thread_info.h
@@ -29,6 +29,7 @@ struct thread_info {
 	struct exec_domain	*exec_domain;	/* execution domain */
 	mm_segment_t		addr_limit;	/* thread address space */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 	__u32			cpu;		/* should always be 0 on m68k */
 	unsigned long		tp_value;	/* thread pointer */
 	struct restart_block    restart_block;
diff --git a/arch/metag/include/asm/thread_info.h b/arch/metag/include/asm/thread_info.h
index 4771133..91729f5 100644
--- a/arch/metag/include/asm/thread_info.h
+++ b/arch/metag/include/asm/thread_info.h
@@ -33,6 +33,7 @@ struct thread_info {
 	unsigned long status;	/* thread-synchronous flags */
 	u32 cpu;		/* current CPU */
 	int preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int pagefault_count;	/* pagefault_disable() levels */
 
 	mm_segment_t addr_limit;	/* thread address space */
 	struct restart_block restart_block;
diff --git a/arch/microblaze/include/asm/thread_info.h b/arch/microblaze/include/asm/thread_info.h
index 8c9d365..f905b02 100644
--- a/arch/microblaze/include/asm/thread_info.h
+++ b/arch/microblaze/include/asm/thread_info.h
@@ -70,6 +70,7 @@ struct thread_info {
 	unsigned long		status; /* thread-synchronous flags */
 	__u32			cpu; /* current CPU */
 	__s32			preempt_count; /* 0 => preemptable,< 0 => BUG*/
+	__s32			pagefault_count; /* pagefault_disable() levels */
 	mm_segment_t		addr_limit; /* thread address space */
 	struct restart_block	restart_block;
 
diff --git a/arch/mips/include/asm/thread_info.h b/arch/mips/include/asm/thread_info.h
index 7de8658..f9f27ac 100644
--- a/arch/mips/include/asm/thread_info.h
+++ b/arch/mips/include/asm/thread_info.h
@@ -28,6 +28,7 @@ struct thread_info {
 	unsigned long		tp_value;	/* thread pointer */
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 
 	mm_segment_t		addr_limit;	/*
 						 * thread address space limit:
diff --git a/arch/mn10300/include/asm/thread_info.h b/arch/mn10300/include/asm/thread_info.h
index bf280ea..f6c03a5 100644
--- a/arch/mn10300/include/asm/thread_info.h
+++ b/arch/mn10300/include/asm/thread_info.h
@@ -45,6 +45,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;		/* current CPU */
 	__s32			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	__s32			pagefault_count;/* pagefault_disable() levels */
 
 	mm_segment_t		addr_limit;	/* thread address space:
 						   0-0xBFFFFFFF for user-thead
diff --git a/arch/openrisc/include/asm/thread_info.h b/arch/openrisc/include/asm/thread_info.h
index d797acc..bdabd6e 100644
--- a/arch/openrisc/include/asm/thread_info.h
+++ b/arch/openrisc/include/asm/thread_info.h
@@ -52,6 +52,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;		/* current CPU */
 	__s32			preempt_count; /* 0 => preemptable, <0 => BUG */
+	__s32			pagefault_count;/* pagefault_disable() levels */
 
 	mm_segment_t		addr_limit; /* thread address space:
 					       0-0x7FFFFFFF for user-thead
diff --git a/arch/parisc/include/asm/thread_info.h b/arch/parisc/include/asm/thread_info.h
index a846118..e37b76b 100644
--- a/arch/parisc/include/asm/thread_info.h
+++ b/arch/parisc/include/asm/thread_info.h
@@ -14,6 +14,7 @@ struct thread_info {
 	mm_segment_t addr_limit;	/* user-level address space limit */
 	__u32 cpu;			/* current CPU */
 	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
+	int pagefault_count;		/* pagefault_disable() levels */
 	struct restart_block restart_block;
 };
 
diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
index b034ecd..e8585fd 100644
--- a/arch/powerpc/include/asm/thread_info.h
+++ b/arch/powerpc/include/asm/thread_info.h
@@ -43,6 +43,7 @@ struct thread_info {
 	int		cpu;			/* cpu we're on */
 	int		preempt_count;		/* 0 => preemptable,
 						   <0 => BUG */
+	int		pagefault_count;	/* pagefault_disable() levels */
 	struct restart_block restart_block;
 	unsigned long	local_flags;		/* private flags for thread */
 
diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
index 4d62fd5..bbf0513f 100644
--- a/arch/s390/include/asm/thread_info.h
+++ b/arch/s390/include/asm/thread_info.h
@@ -39,6 +39,7 @@ struct thread_info {
 	unsigned long		sys_call_table;	/* System call table address */
 	unsigned int		cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 	struct restart_block	restart_block;
 	unsigned int		system_call;
 	__u64			user_timer;
diff --git a/arch/score/include/asm/thread_info.h b/arch/score/include/asm/thread_info.h
index 656b7ad..d7f748d 100644
--- a/arch/score/include/asm/thread_info.h
+++ b/arch/score/include/asm/thread_info.h
@@ -35,6 +35,7 @@ struct thread_info {
 
 	/* 0 => preemptable, < 0 => BUG */
 	int			preempt_count;
+	int			pagefault_count;/* pagefault_disable() levels */
 
 	/*
 	 * thread address space:
diff --git a/arch/sh/include/asm/thread_info.h b/arch/sh/include/asm/thread_info.h
index ad27ffa..682a466 100644
--- a/arch/sh/include/asm/thread_info.h
+++ b/arch/sh/include/asm/thread_info.h
@@ -32,6 +32,7 @@ struct thread_info {
 	__u32			status;		/* thread synchronous flags */
 	__u32			cpu;
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block	restart_block;
 	unsigned long		previous_sp;	/* sp of previous stack in case
diff --git a/arch/sparc/include/asm/thread_info_32.h b/arch/sparc/include/asm/thread_info_32.h
index 025c984..3dc0054 100644
--- a/arch/sparc/include/asm/thread_info_32.h
+++ b/arch/sparc/include/asm/thread_info_32.h
@@ -32,6 +32,7 @@ struct thread_info {
 	int			cpu;		/* cpu we're on */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 	int			softirq_count;
 	int			hardirq_count;
 
@@ -94,15 +95,16 @@ register struct thread_info *current_thread_info_reg asm("g6");
 #define TI_FLAGS	0x0c
 #define TI_CPU		0x10
 #define TI_PREEMPT	0x14	/* preempt_count */
-#define TI_SOFTIRQ	0x18	/* softirq_count */
-#define TI_HARDIRQ	0x1c	/* hardirq_count */
-#define TI_KSP		0x20	/* ksp */
-#define TI_KPC		0x24	/* kpc (ldd'ed with kpc) */
-#define TI_KPSR		0x28	/* kpsr */
-#define TI_KWIM		0x2c	/* kwim (ldd'ed with kpsr) */
-#define TI_REG_WINDOW	0x30
-#define TI_RWIN_SPTRS	0x230
-#define TI_W_SAVED	0x250
+/* #define TI_PAGEFAULT	0x18 */ /* pagefault_count */
+#define TI_SOFTIRQ	0x1c	/* softirq_count */
+#define TI_HARDIRQ	0x20	/* hardirq_count */
+#define TI_KSP		0x24	/* ksp */
+#define TI_KPC		0x28	/* kpc (ldd'ed with kpc) */
+#define TI_KPSR		0x2c	/* kpsr */
+#define TI_KWIM		0x30	/* kwim (ldd'ed with kpsr) */
+#define TI_REG_WINDOW	0x34
+#define TI_RWIN_SPTRS	0x234
+#define TI_W_SAVED	0x254
 /* #define TI_RESTART_BLOCK 0x25n */ /* Nobody cares */
 
 /*
diff --git a/arch/sparc/include/asm/thread_info_64.h b/arch/sparc/include/asm/thread_info_64.h
index 798f027..4b54608 100644
--- a/arch/sparc/include/asm/thread_info_64.h
+++ b/arch/sparc/include/asm/thread_info_64.h
@@ -50,6 +50,7 @@ struct thread_info {
 	__u8			current_ds;
 	__u16			cpu;
 
+	int			pagefault_count;/* pagefault_disable() levels */
 	unsigned long		*utraps;
 
 	struct reg_window 	reg_window[NSWINS];
@@ -87,14 +88,14 @@ struct thread_info {
 #define TI_NEW_CHILD	0x0000003c
 #define TI_CURRENT_DS	0x0000003d
 #define TI_CPU		0x0000003e
-#define TI_UTRAPS	0x00000040
-#define TI_REG_WINDOW	0x00000048
-#define TI_RWIN_SPTRS	0x000003c8
-#define TI_GSR		0x00000400
-#define TI_XFSR		0x00000438
-#define TI_RESTART_BLOCK 0x00000470
-#define TI_KUNA_REGS	0x000004a0
-#define TI_KUNA_INSN	0x000004a8
+#define TI_UTRAPS	0x00000048
+#define TI_REG_WINDOW	0x00000050
+#define TI_RWIN_SPTRS	0x000003d0
+#define TI_GSR		0x00000408
+#define TI_XFSR		0x00000440
+#define TI_RESTART_BLOCK 0x00000478
+#define TI_KUNA_REGS	0x000004a8
+#define TI_KUNA_INSN	0x000004b0
 #define TI_FPREGS	0x000004c0
 
 /* We embed this in the uppermost byte of thread_info->flags */
diff --git a/arch/tile/include/asm/thread_info.h b/arch/tile/include/asm/thread_info.h
index 48e4fd0..57032b6 100644
--- a/arch/tile/include/asm/thread_info.h
+++ b/arch/tile/include/asm/thread_info.h
@@ -33,6 +33,7 @@ struct thread_info {
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;	/* 0 => preemptable,
 						   <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 
 	mm_segment_t		addr_limit;	/* thread address space
 						   (KERNEL_DS or USER_DS) */
diff --git a/arch/um/include/asm/thread_info.h b/arch/um/include/asm/thread_info.h
index 1c5b2a8..90b193c 100644
--- a/arch/um/include/asm/thread_info.h
+++ b/arch/um/include/asm/thread_info.h
@@ -19,6 +19,7 @@ struct thread_info {
 	__u32			cpu;		/* current CPU */
 	int			preempt_count;  /* 0 => preemptable,
 						   <0 => BUG */
+	int			pagefault_count;/* pagefault_disable() levels */
 	mm_segment_t		addr_limit;	/* thread address space:
 					 	   0-0xBFFFFFFF for user
 						   0-0xFFFFFFFF for kernel */
diff --git a/arch/unicore32/include/asm/thread_info.h b/arch/unicore32/include/asm/thread_info.h
index af36d8e..1d50fb3 100644
--- a/arch/unicore32/include/asm/thread_info.h
+++ b/arch/unicore32/include/asm/thread_info.h
@@ -69,6 +69,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable */
 						/* <0 => bug */
+	int			pagefault_count;/* pagefault_disable() levels */
 	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	struct exec_domain	*exec_domain;	/* execution domain */
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 547e344..fa075ab 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -30,6 +30,7 @@ struct thread_info {
 	__u32			status;		/* thread synchronous flags */
 	__u32			cpu;		/* current CPU */
 	int			saved_preempt_count;
+	int			pagefault_count;/* pagefault_disable() levels */
 	mm_segment_t		addr_limit;
 	struct restart_block    restart_block;
 	void __user		*sysenter_return;
diff --git a/arch/xtensa/include/asm/thread_info.h b/arch/xtensa/include/asm/thread_info.h
index 470153e..079e175 100644
--- a/arch/xtensa/include/asm/thread_info.h
+++ b/arch/xtensa/include/asm/thread_info.h
@@ -49,6 +49,7 @@ struct thread_info {
 	unsigned long		status;		/* thread-synchronous flags */
 	__u32			cpu;		/* current CPU */
 	__s32			preempt_count;	/* 0 => preemptable,< 0 => BUG*/
+	__s32			pagefault_count;/* pagefault_disable() levels */
 
 	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block    restart_block;
@@ -71,8 +72,8 @@ struct thread_info {
 #define TI_STATUS	 0x0000000C
 #define TI_CPU		 0x00000010
 #define TI_PRE_COUNT	 0x00000014
-#define TI_ADDR_LIMIT	 0x00000018
-#define TI_RESTART_BLOCK 0x000001C
+#define TI_ADDR_LIMIT	 0x0000001c
+#define TI_RESTART_BLOCK 0x00000020
 
 #endif
 
-- 
1.8.5.5

[PATCH v1 2/5] uaccess: count pagefault_disable() levels in pagefault_count

[David Hildenbrand]

pagefault_disable() and pagefault_enable() have to increment/decrement the
pagefault_count. We keep manipulating the preempt count to retain compability
to existing pagefault handlers. This has to be demangled in separate patches.

It is now possible to verify whether in a pagefault_disable() envionment by
calling pagefault_disabled().

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
---
 include/linux/uaccess.h | 45 ++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 38 insertions(+), 7 deletions(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index ecd3319..1dfc678 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -2,20 +2,45 @@
 #define __LINUX_UACCESS_H__
 
 #include <linux/preempt.h>
+#include <linux/thread_info.h>
 #include <asm/uaccess.h>
 
+static __always_inline int pagefault_count(void)
+{
+	return current_thread_info()->pagefault_count;
+}
+
+static __always_inline int *pagefault_count_ptr(void)
+{
+	return &current_thread_info()->pagefault_count;
+}
+
+static __always_inline void pagefault_count_inc(void)
+{
+	(*pagefault_count_ptr())++;
+}
+
+static __always_inline void pagefault_count_dec(void)
+{
+	(*pagefault_count_ptr())--;
+}
+
 /*
- * These routines enable/disable the pagefault handler in that
- * it will not take any locks and go straight to the fixup table.
+ * These routines enable/disable the pagefault handler. If disabled, it will
+ * not take any locks and go straight to the fixup table.
+ *
+ * We increase the preempt and the pagefault count, to be able to distinguish
+ * whether we run in simple atomic context or in a real pagefault_disable()
+ * context.
+ *
+ * For now, after pagefault_disabled() has been called, we run in atomic
+ * context. User access methods will not sleep.
  *
- * They have great resemblance to the preempt_disable/enable calls
- * and in fact they are identical; this is because currently there is
- * no other way to make the pagefault handlers do this. So we do
- * disable preemption but we don't necessarily care about that.
  */
 static inline void pagefault_disable(void)
 {
 	preempt_count_inc();
+	pagefault_count_inc();
 	/*
 	 * make sure to have issued the store before a pagefault
 	 * can hit.
@@ -25,18 +50,24 @@ static inline void pagefault_disable(void)
 
 static inline void pagefault_enable(void)
 {
-#ifndef CONFIG_PREEMPT
 	/*
 	 * make sure to issue those last loads/stores before enabling
 	 * the pagefault handler again.
 	 */
 	barrier();
+	pagefault_count_dec();
+#ifndef CONFIG_PREEMPT
 	preempt_count_dec();
 #else
 	preempt_enable();
 #endif
 }
 
+/*
+ * Is the pagefault handler disabled? If so, user access methods will not sleep.
+ */
+#define pagefault_disabled() (pagefault_count() != 0)
+
 #ifndef ARCH_HAS_NOCACHE_UACCESS
 
 static inline unsigned long __copy_from_user_inatomic_nocache(void *to,
-- 
1.8.5.5

[PATCH v1 3/5] mm, uaccess: trigger might_sleep() in might_fault() when pagefaults are disabled

[David Hildenbrand]

Commit 662bbcb2747c ("mm, sched: Allow uaccess in atomic with
pagefault_disable()") removed might_sleep() checks for all user access code
(that uses might_fault()).

The reason was to disable wrong "sleep in atomic" warnings in the following
scenario:
    pagefault_disable()
    rc = copy_to_user(...)
    pagefault_enable()

Which is valid, as pagefault_disable() increments the preempt counter and
therefore disables the pagefault handler. copy_to_user() will not sleep and return
an invalid return code if a page is not available.

However, as all might_sleep() checks are removed, CONFIG_DEBUG_ATOMIC_SLEEP
would no longer detect the following scenario:
    spin_lock(&lock);
    rc = copy_to_user(...)
    spin_unlock(&lock)

If the kernel is compiled with preemption turned on, the preempt counter would
be incremented and copy_to_user() would never sleep. However, with preemption
turned off, the preempt counter will not be touched, we will therefore sleep in
atomic context. We really want to enable CONFIG_DEBUG_ATOMIC_SLEEP checks for
user access functions again, otherwise horrible deadlocks might be hard to debug.

Root of all evil is that pagefault_disable() acted almost as preempt_disable(),
depending on preemption being turned on/off.

As we now have pagefault_disabled(), we can use it to distingusih whether user
acces functions might sleep.

Convert might_fault() into a makro that calls __might_fault(), to allow proper
file + line messages in case of a might_sleep() warning. We can't move the code
directly into kernel.h for now, as that results in ugly header recursions we
can't avoid for now.

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
---
 include/linux/kernel.h |  3 ++-
 mm/memory.c            | 19 +++++++------------
 2 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 3d770f55..aa0907e 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -227,7 +227,8 @@ static inline u32 reciprocal_scale(u32 val, u32 ep_ro)
 
 #if defined(CONFIG_MMU) && \
 	(defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP))
-void might_fault(void);
+#define might_fault() __might_fault(__FILE__, __LINE__)
+void __might_fault(const char *file, int line);
 #else
 static inline void might_fault(void) { }
 #endif
diff --git a/mm/memory.c b/mm/memory.c
index d5f2ae9..54dde04 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3700,7 +3700,7 @@ void print_vma_addr(char *prefix, unsigned long ip)
 }
 
 #if defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)
-void might_fault(void)
+void __might_fault(const char *file, int line)
 {
 	/*
 	 * Some code (nfs/sunrpc) uses socket ops on kernel memory while
@@ -3710,21 +3710,16 @@ void might_fault(void)
 	 */
 	if (segment_eq(get_fs(), KERNEL_DS))
 		return;
-
-	/*
-	 * it would be nicer only to annotate paths which are not under
-	 * pagefault_disable, however that requires a larger audit and
-	 * providing helpers like get_user_atomic.
-	 */
-	if (in_atomic())
+	if (unlikely(!pagefault_disabled())) {
+		__might_sleep(file, line, 0);
 		return;
-
-	__might_sleep(__FILE__, __LINE__, 0);
-
+	}
+#if defined(CONFIG_DEBUG_ATOMIC_SLEEP)
 	if (current->mm)
 		might_lock_read(&current->mm->mmap_sem);
+#endif
 }
-EXPORT_SYMBOL(might_fault);
+EXPORT_SYMBOL(__might_fault);
 #endif
 
 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
-- 
1.8.5.5

[PATCH v1 4/5] uaccess: clearify that uaccess may only sleep if pagefaults are not disabled

[David Hildenbrand]

In general, non-atomic variants of user access functions may not sleep if
pagefaults are disabled.

Let's update all relevant comments in uaccess code. This also refelects the
might_sleep() checks in might_fault().

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
---
 arch/avr32/include/asm/uaccess.h      | 12 ++++++----
 arch/hexagon/include/asm/uaccess.h    |  3 ++-
 arch/m32r/include/asm/uaccess.h       | 30 +++++++++++++++--------
 arch/microblaze/include/asm/uaccess.h |  6 +++--
 arch/mips/include/asm/uaccess.h       | 45 +++++++++++++++++++++++------------
 arch/s390/include/asm/uaccess.h       | 15 ++++++++----
 arch/score/include/asm/uaccess.h      | 15 ++++++++----
 arch/tile/include/asm/uaccess.h       | 21 ++++++++++------
 arch/x86/include/asm/uaccess.h        | 15 ++++++++----
 arch/x86/include/asm/uaccess_32.h     |  6 +++--
 arch/x86/lib/usercopy_32.c            |  6 +++--
 lib/strnlen_user.c                    |  6 +++--
 12 files changed, 120 insertions(+), 60 deletions(-)

diff --git a/arch/avr32/include/asm/uaccess.h b/arch/avr32/include/asm/uaccess.h
index 245b2ee..6b6dd58 100644
--- a/arch/avr32/include/asm/uaccess.h
+++ b/arch/avr32/include/asm/uaccess.h
@@ -97,7 +97,8 @@ static inline __kernel_size_t __copy_from_user(void *to,
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -116,7 +117,8 @@ static inline __kernel_size_t __copy_from_user(void *to,
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -136,7 +138,8 @@ static inline __kernel_size_t __copy_from_user(void *to,
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -158,7 +161,8 @@ static inline __kernel_size_t __copy_from_user(void *to,
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
diff --git a/arch/hexagon/include/asm/uaccess.h b/arch/hexagon/include/asm/uaccess.h
index e4127e4..af98618 100644
--- a/arch/hexagon/include/asm/uaccess.h
+++ b/arch/hexagon/include/asm/uaccess.h
@@ -36,7 +36,8 @@
  * @addr: User space pointer to start of block to check
  * @size: Size of block to check
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ * disabled.
  *
  * Checks if a pointer to a block of memory in user space is valid.
  *
diff --git a/arch/m32r/include/asm/uaccess.h b/arch/m32r/include/asm/uaccess.h
index 84fe7ba..83bfa33 100644
--- a/arch/m32r/include/asm/uaccess.h
+++ b/arch/m32r/include/asm/uaccess.h
@@ -91,7 +91,8 @@ static inline void set_fs(mm_segment_t s)
  * @addr: User space pointer to start of block to check
  * @size: Size of block to check
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Checks if a pointer to a block of memory in user space is valid.
  *
@@ -155,7 +156,8 @@ extern int fixup_exception(struct pt_regs *regs);
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -175,7 +177,8 @@ extern int fixup_exception(struct pt_regs *regs);
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -194,7 +197,8 @@ extern int fixup_exception(struct pt_regs *regs);
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -274,7 +278,8 @@ do {									\
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -568,7 +573,8 @@ unsigned long __generic_copy_from_user(void *, const void __user *, unsigned lon
  * @from: Source address, in kernel space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from kernel space to user space.  Caller must check
  * the specified block with access_ok() before calling this function.
@@ -588,7 +594,8 @@ unsigned long __generic_copy_from_user(void *, const void __user *, unsigned lon
  * @from: Source address, in kernel space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from kernel space to user space.
  *
@@ -606,7 +613,8 @@ unsigned long __generic_copy_from_user(void *, const void __user *, unsigned lon
  * @from: Source address, in user space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to kernel space.  Caller must check
  * the specified block with access_ok() before calling this function.
@@ -626,7 +634,8 @@ unsigned long __generic_copy_from_user(void *, const void __user *, unsigned lon
  * @from: Source address, in user space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to kernel space.
  *
@@ -677,7 +686,8 @@ unsigned long clear_user(void __user *mem, unsigned long len);
  * strlen_user: - Get the size of a string in user space.
  * @str: The string to measure.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Get the size of a NUL-terminated string in user space.
  *
diff --git a/arch/microblaze/include/asm/uaccess.h b/arch/microblaze/include/asm/uaccess.h
index 59a89a6..53bfbb8 100644
--- a/arch/microblaze/include/asm/uaccess.h
+++ b/arch/microblaze/include/asm/uaccess.h
@@ -178,7 +178,8 @@ extern long __user_bad(void);
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -290,7 +291,8 @@ extern long __user_bad(void);
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h
index 22a5624..eded117 100644
--- a/arch/mips/include/asm/uaccess.h
+++ b/arch/mips/include/asm/uaccess.h
@@ -103,7 +103,8 @@ extern u64 __ua_limit;
  * @addr: User space pointer to start of block to check
  * @size: Size of block to check
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Checks if a pointer to a block of memory in user space is valid.
  *
@@ -138,7 +139,8 @@ extern u64 __ua_limit;
  * @x:	 Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -157,7 +159,8 @@ extern u64 __ua_limit;
  * @x:	 Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -177,7 +180,8 @@ extern u64 __ua_limit;
  * @x:	 Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -199,7 +203,8 @@ extern u64 __ua_limit;
  * @x:	 Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -498,7 +503,8 @@ extern void __put_user_unknown(void);
  * @x:	 Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -517,7 +523,8 @@ extern void __put_user_unknown(void);
  * @x:	 Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -537,7 +544,8 @@ extern void __put_user_unknown(void);
  * @x:	 Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -559,7 +567,8 @@ extern void __put_user_unknown(void);
  * @x:	 Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -815,7 +824,8 @@ extern size_t __copy_user(void *__to, const void *__from, size_t __n);
  * @from: Source address, in kernel space.
  * @n:	  Number of bytes to copy.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from kernel space to user space.  Caller must check
  * the specified block with access_ok() before calling this function.
@@ -888,7 +898,8 @@ extern size_t __copy_user_inatomic(void *__to, const void *__from, size_t __n);
  * @from: Source address, in kernel space.
  * @n:	  Number of bytes to copy.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from kernel space to user space.
  *
@@ -1075,7 +1086,8 @@ extern size_t __copy_in_user_eva(void *__to, const void *__from, size_t __n);
  * @from: Source address, in user space.
  * @n:	  Number of bytes to copy.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to kernel space.  Caller must check
  * the specified block with access_ok() before calling this function.
@@ -1107,7 +1119,8 @@ extern size_t __copy_in_user_eva(void *__to, const void *__from, size_t __n);
  * @from: Source address, in user space.
  * @n:	  Number of bytes to copy.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to kernel space.
  *
@@ -1356,7 +1369,8 @@ static inline long __strlen_user(const char __user *s)
  * strlen_user: - Get the size of a string in user space.
  * @str: The string to measure.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Get the size of a NUL-terminated string in user space.
  *
@@ -1425,7 +1439,8 @@ static inline long __strnlen_user(const char __user *s, long n)
  * strnlen_user: - Get the size of a string in user space.
  * @str: The string to measure.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Get the size of a NUL-terminated string in user space.
  *
diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index cd4c68e..1291da5 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -98,7 +98,8 @@ static inline unsigned long extable_fixup(const struct exception_table_entry *x)
  * @from: Source address, in user space.
  * @n:	  Number of bytes to copy.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to kernel space.  Caller must check
  * the specified block with access_ok() before calling this function.
@@ -118,7 +119,8 @@ unsigned long __must_check __copy_from_user(void *to, const void __user *from,
  * @from: Source address, in kernel space.
  * @n:	  Number of bytes to copy.
  *
- * Context: User context only.	This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from kernel space to user space.  Caller must check
  * the specified block with access_ok() before calling this function.
@@ -264,7 +266,8 @@ int __get_user_bad(void) __attribute__((noreturn));
  * @from: Source address, in kernel space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from kernel space to user space.
  *
@@ -290,7 +293,8 @@ __compiletime_warning("copy_from_user() buffer size is not provably correct")
  * @from: Source address, in user space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to kernel space.
  *
@@ -348,7 +352,8 @@ static inline unsigned long strnlen_user(const char __user *src, unsigned long n
  * strlen_user: - Get the size of a string in user space.
  * @str: The string to measure.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Get the size of a NUL-terminated string in user space.
  *
diff --git a/arch/score/include/asm/uaccess.h b/arch/score/include/asm/uaccess.h
index ab66ddd..010a800 100644
--- a/arch/score/include/asm/uaccess.h
+++ b/arch/score/include/asm/uaccess.h
@@ -36,7 +36,8 @@
  * @addr: User space pointer to start of block to check
  * @size: Size of block to check
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Checks if a pointer to a block of memory in user space is valid.
  *
@@ -61,7 +62,8 @@
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -79,7 +81,8 @@
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -98,7 +101,8 @@
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -119,7 +123,8 @@
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
diff --git a/arch/tile/include/asm/uaccess.h b/arch/tile/include/asm/uaccess.h
index b6cde32..9efe668 100644
--- a/arch/tile/include/asm/uaccess.h
+++ b/arch/tile/include/asm/uaccess.h
@@ -78,7 +78,8 @@ int __range_ok(unsigned long addr, unsigned long size);
  * @addr: User space pointer to start of block to check
  * @size: Size of block to check
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Checks if a pointer to a block of memory in user space is valid.
  *
@@ -192,7 +193,8 @@ extern int __get_user_bad(void)
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -272,7 +274,8 @@ extern int __put_user_bad(void)
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -327,7 +330,8 @@ extern int __put_user_bad(void)
  * @from: Source address, in kernel space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from kernel space to user space.  Caller must check
  * the specified block with access_ok() before calling this function.
@@ -363,7 +367,8 @@ copy_to_user(void __user *to, const void *from, unsigned long n)
  * @from: Source address, in user space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to kernel space.  Caller must check
  * the specified block with access_ok() before calling this function.
@@ -434,7 +439,8 @@ static inline unsigned long __must_check copy_from_user(void *to,
  * @from: Source address, in user space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to user space.  Caller must check
  * the specified blocks with access_ok() before calling this function.
@@ -466,7 +472,8 @@ copy_in_user(void __user *to, const void __user *from, unsigned long n)
  * strlen_user: - Get the size of a string in user space.
  * @str: The string to measure.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Get the size of a NUL-terminated string in user space.
  *
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 0d592e0..014d8cb 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -74,7 +74,8 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
  * @addr: User space pointer to start of block to check
  * @size: Size of block to check
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Checks if a pointer to a block of memory in user space is valid.
  *
@@ -145,7 +146,8 @@ __typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL))
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -240,7 +242,8 @@ extern void __put_user_8(void);
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
@@ -455,7 +458,8 @@ struct __large_struct { unsigned long buf[100]; };
  * @x:   Variable to store result.
  * @ptr: Source address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple variable from user space to kernel
  * space.  It supports simple types like char and int, but not larger
@@ -479,7 +483,8 @@ struct __large_struct { unsigned long buf[100]; };
  * @x:   Value to copy to user space.
  * @ptr: Destination address, in user space.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * This macro copies a single simple value from kernel space to user
  * space.  It supports simple types like char and int, but not larger
diff --git a/arch/x86/include/asm/uaccess_32.h b/arch/x86/include/asm/uaccess_32.h
index 3c03a5d..ae5b37f 100644
--- a/arch/x86/include/asm/uaccess_32.h
+++ b/arch/x86/include/asm/uaccess_32.h
@@ -70,7 +70,8 @@ __copy_to_user_inatomic(void __user *to, const void *from, unsigned long n)
  * @from: Source address, in kernel space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from kernel space to user space.  Caller must check
  * the specified block with access_ok() before calling this function.
@@ -117,7 +118,8 @@ __copy_from_user_inatomic(void *to, const void __user *from, unsigned long n)
  * @from: Source address, in user space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to kernel space.  Caller must check
  * the specified block with access_ok() before calling this function.
diff --git a/arch/x86/lib/usercopy_32.c b/arch/x86/lib/usercopy_32.c
index e2f5e21..64ba86e 100644
--- a/arch/x86/lib/usercopy_32.c
+++ b/arch/x86/lib/usercopy_32.c
@@ -647,7 +647,8 @@ EXPORT_SYMBOL(__copy_from_user_ll_nocache_nozero);
  * @from: Source address, in kernel space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from kernel space to user space.
  *
@@ -668,7 +669,8 @@ EXPORT_SYMBOL(_copy_to_user);
  * @from: Source address, in user space.
  * @n:    Number of bytes to copy.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Copy data from user space to kernel space.
  *
diff --git a/lib/strnlen_user.c b/lib/strnlen_user.c
index a28df52..0013abd 100644
--- a/lib/strnlen_user.c
+++ b/lib/strnlen_user.c
@@ -84,7 +84,8 @@ static inline long do_strnlen_user(const char __user *src, unsigned long count,
  * @str: The string to measure.
  * @count: Maximum count (including NUL character)
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Get the size of a NUL-terminated string in user space.
  *
@@ -113,7 +114,8 @@ EXPORT_SYMBOL(strnlen_user);
  * strlen_user: - Get the size of a user string INCLUDING final NUL.
  * @str: The string to measure.
  *
- * Context: User context only.  This function may sleep.
+ * Context: User context only. This function may sleep if pagefaults are not
+ *          disabled.
  *
  * Get the size of a NUL-terminated string in user space.
  *
-- 
1.8.5.5

[PATCH v1 5/5] uaccess: CONFIG_DEBUG_PAGEFAULT_COUNT to debug pagefault_count

[David Hildenbrand]

This patch introduces CONFIG_DEBUG_PAGEFAULT_COUNT, to detect over-/underflows
in the pagefault_count resulting from a wrong usage of pagefault_enable() and
pagefault_disable().

Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
---
 include/linux/uaccess.h |  8 +++++++-
 lib/Kconfig.debug       |  9 +++++++++
 mm/maccess.c            | 11 +++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 1dfc678..6ffb90b 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -20,11 +20,17 @@ static __always_inline void pagefault_count_inc(void)
 	(*pagefault_count_ptr())++;
 }
 
-static __always_inline void pagefault_count_dec(void)
+static __always_inline void __pagefault_count_dec(void)
 {
 	(*pagefault_count_ptr())--;
 }
 
+#ifdef CONFIG_DEBUG_PAGEFAULT_COUNT
+extern void pagefault_count_dec(void);
+#else
+#define pagefault_count_dec() __pagefault_count_dec()
+#endif
+
 /*
  * These routines enable/disable the pagefault handler. If disabled, it will
  * not take any locks and go straight to the fixup table.
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 4e35a5d..529e9d4 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -860,6 +860,15 @@ config DEBUG_PREEMPT
 	  if kernel code uses it in a preemption-unsafe way. Also, the kernel
 	  will detect preemption count underflows.
 
+config DEBUG_PAGEFAULT_COUNT
+	bool "Debug pagefault_disable / pagefault_enable"
+	depends on DEBUG_KERNEL
+	default n
+	help
+	  If you say Y here then the kernel will detect pagefault count
+	  over-/underflows and therefore non-matching pagefault_enable() and
+	  pagefault_disable() calls.
+
 menu "Lock Debugging (spinlocks, mutexes, etc...)"
 
 config DEBUG_RT_MUTEXES
diff --git a/mm/maccess.c b/mm/maccess.c
index d53adf9..4b72aa1 100644
--- a/mm/maccess.c
+++ b/mm/maccess.c
@@ -5,6 +5,17 @@
 #include <linux/mm.h>
 #include <linux/uaccess.h>
 
+#ifdef CONFIG_DEBUG_PAGEFAULT_COUNT
+void pagefault_count_dec(void)
+{
+	__pagefault_count_dec();
+
+	/* underflow / previous overflow ? */
+	WARN_ON(pagefault_count() < 0);
+}
+EXPORT_SYMBOL(pagefault_count_dec);
+#endif
+
 /**
  * probe_kernel_read(): safely attempt to read from a location
  * @dst: pointer to the buffer that shall take the data
-- 
1.8.5.5

Re: [PATCH v1 3/5] mm, uaccess: trigger might_sleep() in might_fault() when pagefaults are disabled

[Heiko Carstens]

On Fri, Dec 05, 2014 at 12:18:07PM +0100, David Hildenbrand wrote:
> -void might_fault(void)
> +void __might_fault(const char *file, int line)
>  {
>  	/*
>  	 * Some code (nfs/sunrpc) uses socket ops on kernel memory while
> @@ -3710,21 +3710,16 @@ void might_fault(void)
>  	 */
>  	if (segment_eq(get_fs(), KERNEL_DS))
>  		return;
> -
> -	/*
> -	 * it would be nicer only to annotate paths which are not under
> -	 * pagefault_disable, however that requires a larger audit and
> -	 * providing helpers like get_user_atomic.
> -	 */
> -	if (in_atomic())
> +	if (unlikely(!pagefault_disabled())) {
> +		__might_sleep(file, line, 0);
>  		return;
> -
> -	__might_sleep(__FILE__, __LINE__, 0);
> -
> +	}

This should be likely() instead of unlikely(), no?
I'd rather write this

	if (pagefault_disabled())
 		return;
	__might_sleep(file, line, 0);

and leave the likely stuff completely away.

Re: [PATCH v1 3/5] mm, uaccess: trigger might_sleep() in might_fault() when pagefaults are disabled

[David Hildenbrand]

> On Fri, Dec 05, 2014 at 12:18:07PM +0100, David Hildenbrand wrote:
> > -void might_fault(void)
> > +void __might_fault(const char *file, int line)
> >  {
> >  	/*
> >  	 * Some code (nfs/sunrpc) uses socket ops on kernel memory while
> > @@ -3710,21 +3710,16 @@ void might_fault(void)
> >  	 */
> >  	if (segment_eq(get_fs(), KERNEL_DS))
> >  		return;
> > -
> > -	/*
> > -	 * it would be nicer only to annotate paths which are not under
> > -	 * pagefault_disable, however that requires a larger audit and
> > -	 * providing helpers like get_user_atomic.
> > -	 */
> > -	if (in_atomic())
> > +	if (unlikely(!pagefault_disabled())) {
> > +		__might_sleep(file, line, 0);
> >  		return;
> > -
> > -	__might_sleep(__FILE__, __LINE__, 0);
> > -
> > +	}
> 
> This should be likely() instead of unlikely(), no?
> I'd rather write this
> 
> 	if (pagefault_disabled())
>  		return;
> 	__might_sleep(file, line, 0);
> 
> and leave the likely stuff completely away.

Makes perfect sense!

Thanks!

David

RE: [PATCH v1 3/5] mm, uaccess: trigger might_sleep() in might_fault() when pagefaults are disabled

[David Laight]

From: David Hildenbrand [...
> > This should be likely() instead of unlikely(), no?
> > I'd rather write this
> >
> > 	if (pagefault_disabled())
> >  		return;
> > 	__might_sleep(file, line, 0);
> >
> > and leave the likely stuff completely away.
> 
> Makes perfect sense!

>From my experience of getting (an older version of) gcc to emit
'correctly' statically predicted branches I found that code that
looks like (I don't think return/goto make any difference):

	If (unlikely(condition)) {
		code;
	}
	more_code;

is compile with a forwards conditional branch (ie ignoring the unlikely()).
Similarly 'if () continue' is likely to generate a 'predicted taken'
backwards conditional branch.

To get the desired effect you need a non-empty 'else' part, an assembler
comment will suffice, eg: asm volatile("# comment").

	David

Re: [PATCH v1 3/5] mm, uaccess: trigger might_sleep() in might_fault() when pagefaults are disabled

[David Hildenbrand]

> From: David Hildenbrand [...
> > > This should be likely() instead of unlikely(), no?
> > > I'd rather write this
> > >
> > > 	if (pagefault_disabled())
> > >  		return;
> > > 	__might_sleep(file, line, 0);
> > >
> > > and leave the likely stuff completely away.
> > 
> > Makes perfect sense!
> 
> From my experience of getting (an older version of) gcc to emit
> 'correctly' statically predicted branches I found that code that
> looks like (I don't think return/goto make any difference):
> 
> 	If (unlikely(condition)) {
> 		code;
> 	}
> 	more_code;
> 
> is compile with a forwards conditional branch (ie ignoring the unlikely()).
> Similarly 'if () continue' is likely to generate a 'predicted taken'
> backwards conditional branch.
> 
> To get the desired effect you need a non-empty 'else' part, an assembler
> comment will suffice, eg: asm volatile("# comment").
> 
> 	David
> 
> 
> 

Thanks for the hint David!

I'm going to drop that unlikely and simply replace in_atomic() by
pagefault_disabled() - will also keep the change minimal!

David

Re: [PATCH v1 1/5] uaccess: add pagefault_count to thread_info

[Christian Borntraeger]

Am 05.12.2014 um 12:18 schrieb David Hildenbrand:
> This patch adds the pagefault_count to the thread_info of all
> architectures. It will be used to count the pagefault_disable() levels
> on a per-thread basis.
> 
> We are not reusing the preempt_count as this is per cpu on x86 and we want to
> demangle pagefault_disable() from preemption in the future.
> 
> Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
> ---
>  arch/alpha/include/asm/thread_info.h      |  1 +
>  arch/arc/include/asm/thread_info.h        |  1 +
>  arch/arm/include/asm/thread_info.h        |  1 +
>  arch/arm64/include/asm/thread_info.h      |  1 +
>  arch/avr32/include/asm/thread_info.h      |  1 +
>  arch/blackfin/include/asm/thread_info.h   |  1 +
>  arch/c6x/include/asm/thread_info.h        |  1 +
>  arch/cris/include/asm/thread_info.h       |  1 +
>  arch/frv/include/asm/thread_info.h        |  1 +
>  arch/hexagon/include/asm/thread_info.h    |  1 +
>  arch/ia64/include/asm/thread_info.h       |  1 +
>  arch/m32r/include/asm/thread_info.h       |  5 +++--
>  arch/m68k/include/asm/thread_info.h       |  1 +
>  arch/metag/include/asm/thread_info.h      |  1 +
>  arch/microblaze/include/asm/thread_info.h |  1 +
>  arch/mips/include/asm/thread_info.h       |  1 +
>  arch/mn10300/include/asm/thread_info.h    |  1 +
>  arch/openrisc/include/asm/thread_info.h   |  1 +
>  arch/parisc/include/asm/thread_info.h     |  1 +
>  arch/powerpc/include/asm/thread_info.h    |  1 +
>  arch/s390/include/asm/thread_info.h       |  1 +
>  arch/score/include/asm/thread_info.h      |  1 +
>  arch/sh/include/asm/thread_info.h         |  1 +
>  arch/sparc/include/asm/thread_info_32.h   | 20 +++++++++++---------
>  arch/sparc/include/asm/thread_info_64.h   | 17 +++++++++--------

Maybe its easier to put the pagefault count at the end of the thread_info struct to make the patch smaller and easier to review for thoses architectures that have hand-maintained asm offsets? 


>  arch/tile/include/asm/thread_info.h       |  1 +
>  arch/um/include/asm/thread_info.h         |  1 +
>  arch/unicore32/include/asm/thread_info.h  |  1 +
>  arch/x86/include/asm/thread_info.h        |  1 +
>  arch/xtensa/include/asm/thread_info.h     |  5 +++--
>  30 files changed, 52 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/alpha/include/asm/thread_info.h b/arch/alpha/include/asm/thread_info.h
> index 48bbea6..1830671 100644
> --- a/arch/alpha/include/asm/thread_info.h
> +++ b/arch/alpha/include/asm/thread_info.h
> @@ -22,6 +22,7 @@ struct thread_info {
>  	mm_segment_t		addr_limit;	/* thread address space */
>  	unsigned		cpu;		/* current CPU */
>  	int			preempt_count; /* 0 => preemptable, <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	unsigned int		status;		/* thread-synchronous flags */
> 
>  	int bpt_nsaved;
> diff --git a/arch/arc/include/asm/thread_info.h b/arch/arc/include/asm/thread_info.h
> index 02bc5ec..2fde704 100644
> --- a/arch/arc/include/asm/thread_info.h
> +++ b/arch/arc/include/asm/thread_info.h
> @@ -41,6 +41,7 @@
>  struct thread_info {
>  	unsigned long flags;		/* low level flags */
>  	int preempt_count;		/* 0 => preemptable, <0 => BUG */
> +	int pagefault_count;		/* pagefault_disable() levels */
>  	struct task_struct *task;	/* main task structure */
>  	mm_segment_t addr_limit;	/* thread address space */
>  	struct exec_domain *exec_domain;/* execution domain */
> diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
> index ce73ab6..bf47d2d 100644
> --- a/arch/arm/include/asm/thread_info.h
> +++ b/arch/arm/include/asm/thread_info.h
> @@ -51,6 +51,7 @@ struct cpu_context_save {
>  struct thread_info {
>  	unsigned long		flags;		/* low level flags */
>  	int			preempt_count;	/* 0 => preemptable, <0 => bug */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	mm_segment_t		addr_limit;	/* address limit */
>  	struct task_struct	*task;		/* main task structure */
>  	struct exec_domain	*exec_domain;	/* execution domain */
> diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
> index 459bf8e..2469f15 100644
> --- a/arch/arm64/include/asm/thread_info.h
> +++ b/arch/arm64/include/asm/thread_info.h
> @@ -50,6 +50,7 @@ struct thread_info {
>  	struct exec_domain	*exec_domain;	/* execution domain */
>  	struct restart_block	restart_block;
>  	int			preempt_count;	/* 0 => preemptable, <0 => bug */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	int			cpu;		/* cpu */
>  };
> 
> diff --git a/arch/avr32/include/asm/thread_info.h b/arch/avr32/include/asm/thread_info.h
> index a978f3f..0c1d6f7 100644
> --- a/arch/avr32/include/asm/thread_info.h
> +++ b/arch/avr32/include/asm/thread_info.h
> @@ -25,6 +25,7 @@ struct thread_info {
>  	unsigned long		flags;		/* low level flags */
>  	__u32			cpu;
>  	__s32			preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	__s32			pagefault_count;/* pagefault_disable() levels */
>  	__u32			rar_saved;	/* return address... */
>  	__u32			rsr_saved;	/* ...and status register
>  						   saved by debug handler
> diff --git a/arch/blackfin/include/asm/thread_info.h b/arch/blackfin/include/asm/thread_info.h
> index 55f473b..3ba26aa 100644
> --- a/arch/blackfin/include/asm/thread_info.h
> +++ b/arch/blackfin/include/asm/thread_info.h
> @@ -41,6 +41,7 @@ struct thread_info {
>  	unsigned long flags;	/* low level flags */
>  	int cpu;		/* cpu we're on */
>  	int preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	int pagefault_count;	/* pagefault_disable() levels */
>  	mm_segment_t addr_limit;	/* address limit */
>  	struct restart_block restart_block;
>  #ifndef CONFIG_SMP
> diff --git a/arch/c6x/include/asm/thread_info.h b/arch/c6x/include/asm/thread_info.h
> index d4e9ef8..6b2dcac 100644
> --- a/arch/c6x/include/asm/thread_info.h
> +++ b/arch/c6x/include/asm/thread_info.h
> @@ -44,6 +44,7 @@ struct thread_info {
>  	unsigned long		flags;		/* low level flags */
>  	int			cpu;		/* cpu we're on */
>  	int			preempt_count;	/* 0 = preemptable, <0 = BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	mm_segment_t		addr_limit;	/* thread address space */
>  	struct restart_block	restart_block;
>  };
> diff --git a/arch/cris/include/asm/thread_info.h b/arch/cris/include/asm/thread_info.h
> index 55dede1..3356902 100644
> --- a/arch/cris/include/asm/thread_info.h
> +++ b/arch/cris/include/asm/thread_info.h
> @@ -32,6 +32,7 @@ struct thread_info {
>  	unsigned long		flags;		/* low level flags */
>  	__u32			cpu;		/* current CPU */
>  	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	__u32			tls;		/* TLS for this thread */
> 
>  	mm_segment_t		addr_limit;	/* thread address space:
> diff --git a/arch/frv/include/asm/thread_info.h b/arch/frv/include/asm/thread_info.h
> index af29e17..79a97ee 100644
> --- a/arch/frv/include/asm/thread_info.h
> +++ b/arch/frv/include/asm/thread_info.h
> @@ -36,6 +36,7 @@ struct thread_info {
>  	unsigned long		status;		/* thread-synchronous flags */
>  	__u32			cpu;		/* current CPU */
>  	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
> 
>  	mm_segment_t		addr_limit;	/* thread address space:
>  						 * 0-0xBFFFFFFF for user-thead
> diff --git a/arch/hexagon/include/asm/thread_info.h b/arch/hexagon/include/asm/thread_info.h
> index a59dad3..d54042e 100644
> --- a/arch/hexagon/include/asm/thread_info.h
> +++ b/arch/hexagon/include/asm/thread_info.h
> @@ -51,6 +51,7 @@ struct thread_info {
>  	unsigned long		flags;          /* low level flags */
>  	__u32                   cpu;            /* current cpu */
>  	int                     preempt_count;  /* 0=>preemptible,<0=>BUG */
> +	int                     pagefault_count;/* pagefault_disable() levels */
>  	mm_segment_t            addr_limit;     /* segmentation sux */
>  	/*
>  	 * used for syscalls somehow;
> diff --git a/arch/ia64/include/asm/thread_info.h b/arch/ia64/include/asm/thread_info.h
> index 5b17418..14f128c 100644
> --- a/arch/ia64/include/asm/thread_info.h
> +++ b/arch/ia64/include/asm/thread_info.h
> @@ -27,6 +27,7 @@ struct thread_info {
>  	__u32 status;			/* Thread synchronous flags */
>  	mm_segment_t addr_limit;	/* user-level address space limit */
>  	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
> +	int pagefault_count;		/* pagefault_disable() levels */
>  	struct restart_block restart_block;
>  #ifdef CONFIG_VIRT_CPU_ACCOUNTING_NATIVE
>  	__u64 ac_stamp;
> diff --git a/arch/m32r/include/asm/thread_info.h b/arch/m32r/include/asm/thread_info.h
> index 0017170..a1ec910 100644
> --- a/arch/m32r/include/asm/thread_info.h
> +++ b/arch/m32r/include/asm/thread_info.h
> @@ -29,6 +29,7 @@ struct thread_info {
>  	unsigned long		status;		/* thread-synchronous flags */
>  	__u32			cpu;		/* current CPU */
>  	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
> 
>  	mm_segment_t		addr_limit;	/* thread address space:
>  					 	   0-0xBFFFFFFF for user-thread
> @@ -48,8 +49,8 @@ struct thread_info {
>  #define TI_STATUS	0x0000000C
>  #define TI_CPU		0x00000010
>  #define TI_PRE_COUNT	0x00000014
> -#define TI_ADDR_LIMIT	0x00000018
> -#define TI_RESTART_BLOCK 0x000001C
> +#define TI_ADDR_LIMIT	0x0000001C
> +#define TI_RESTART_BLOCK 0x0000020
> 
>  #endif
> 
> diff --git a/arch/m68k/include/asm/thread_info.h b/arch/m68k/include/asm/thread_info.h
> index 21a4784..5a6a203 100644
> --- a/arch/m68k/include/asm/thread_info.h
> +++ b/arch/m68k/include/asm/thread_info.h
> @@ -29,6 +29,7 @@ struct thread_info {
>  	struct exec_domain	*exec_domain;	/* execution domain */
>  	mm_segment_t		addr_limit;	/* thread address space */
>  	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	__u32			cpu;		/* should always be 0 on m68k */
>  	unsigned long		tp_value;	/* thread pointer */
>  	struct restart_block    restart_block;
> diff --git a/arch/metag/include/asm/thread_info.h b/arch/metag/include/asm/thread_info.h
> index 4771133..91729f5 100644
> --- a/arch/metag/include/asm/thread_info.h
> +++ b/arch/metag/include/asm/thread_info.h
> @@ -33,6 +33,7 @@ struct thread_info {
>  	unsigned long status;	/* thread-synchronous flags */
>  	u32 cpu;		/* current CPU */
>  	int preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	int pagefault_count;	/* pagefault_disable() levels */
> 
>  	mm_segment_t addr_limit;	/* thread address space */
>  	struct restart_block restart_block;
> diff --git a/arch/microblaze/include/asm/thread_info.h b/arch/microblaze/include/asm/thread_info.h
> index 8c9d365..f905b02 100644
> --- a/arch/microblaze/include/asm/thread_info.h
> +++ b/arch/microblaze/include/asm/thread_info.h
> @@ -70,6 +70,7 @@ struct thread_info {
>  	unsigned long		status; /* thread-synchronous flags */
>  	__u32			cpu; /* current CPU */
>  	__s32			preempt_count; /* 0 => preemptable,< 0 => BUG*/
> +	__s32			pagefault_count; /* pagefault_disable() levels */
>  	mm_segment_t		addr_limit; /* thread address space */
>  	struct restart_block	restart_block;
> 
> diff --git a/arch/mips/include/asm/thread_info.h b/arch/mips/include/asm/thread_info.h
> index 7de8658..f9f27ac 100644
> --- a/arch/mips/include/asm/thread_info.h
> +++ b/arch/mips/include/asm/thread_info.h
> @@ -28,6 +28,7 @@ struct thread_info {
>  	unsigned long		tp_value;	/* thread pointer */
>  	__u32			cpu;		/* current CPU */
>  	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
> 
>  	mm_segment_t		addr_limit;	/*
>  						 * thread address space limit:
> diff --git a/arch/mn10300/include/asm/thread_info.h b/arch/mn10300/include/asm/thread_info.h
> index bf280ea..f6c03a5 100644
> --- a/arch/mn10300/include/asm/thread_info.h
> +++ b/arch/mn10300/include/asm/thread_info.h
> @@ -45,6 +45,7 @@ struct thread_info {
>  	unsigned long		flags;		/* low level flags */
>  	__u32			cpu;		/* current CPU */
>  	__s32			preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	__s32			pagefault_count;/* pagefault_disable() levels */
> 
>  	mm_segment_t		addr_limit;	/* thread address space:
>  						   0-0xBFFFFFFF for user-thead
> diff --git a/arch/openrisc/include/asm/thread_info.h b/arch/openrisc/include/asm/thread_info.h
> index d797acc..bdabd6e 100644
> --- a/arch/openrisc/include/asm/thread_info.h
> +++ b/arch/openrisc/include/asm/thread_info.h
> @@ -52,6 +52,7 @@ struct thread_info {
>  	unsigned long		flags;		/* low level flags */
>  	__u32			cpu;		/* current CPU */
>  	__s32			preempt_count; /* 0 => preemptable, <0 => BUG */
> +	__s32			pagefault_count;/* pagefault_disable() levels */
> 
>  	mm_segment_t		addr_limit; /* thread address space:
>  					       0-0x7FFFFFFF for user-thead
> diff --git a/arch/parisc/include/asm/thread_info.h b/arch/parisc/include/asm/thread_info.h
> index a846118..e37b76b 100644
> --- a/arch/parisc/include/asm/thread_info.h
> +++ b/arch/parisc/include/asm/thread_info.h
> @@ -14,6 +14,7 @@ struct thread_info {
>  	mm_segment_t addr_limit;	/* user-level address space limit */
>  	__u32 cpu;			/* current CPU */
>  	int preempt_count;		/* 0=premptable, <0=BUG; will also serve as bh-counter */
> +	int pagefault_count;		/* pagefault_disable() levels */
>  	struct restart_block restart_block;
>  };
> 
> diff --git a/arch/powerpc/include/asm/thread_info.h b/arch/powerpc/include/asm/thread_info.h
> index b034ecd..e8585fd 100644
> --- a/arch/powerpc/include/asm/thread_info.h
> +++ b/arch/powerpc/include/asm/thread_info.h
> @@ -43,6 +43,7 @@ struct thread_info {
>  	int		cpu;			/* cpu we're on */
>  	int		preempt_count;		/* 0 => preemptable,
>  						   <0 => BUG */
> +	int		pagefault_count;	/* pagefault_disable() levels */
>  	struct restart_block restart_block;
>  	unsigned long	local_flags;		/* private flags for thread */
> 
> diff --git a/arch/s390/include/asm/thread_info.h b/arch/s390/include/asm/thread_info.h
> index 4d62fd5..bbf0513f 100644
> --- a/arch/s390/include/asm/thread_info.h
> +++ b/arch/s390/include/asm/thread_info.h
> @@ -39,6 +39,7 @@ struct thread_info {
>  	unsigned long		sys_call_table;	/* System call table address */
>  	unsigned int		cpu;		/* current CPU */
>  	int			preempt_count;	/* 0 => preemptable, <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	struct restart_block	restart_block;
>  	unsigned int		system_call;
>  	__u64			user_timer;
> diff --git a/arch/score/include/asm/thread_info.h b/arch/score/include/asm/thread_info.h
> index 656b7ad..d7f748d 100644
> --- a/arch/score/include/asm/thread_info.h
> +++ b/arch/score/include/asm/thread_info.h
> @@ -35,6 +35,7 @@ struct thread_info {
> 
>  	/* 0 => preemptable, < 0 => BUG */
>  	int			preempt_count;
> +	int			pagefault_count;/* pagefault_disable() levels */
> 
>  	/*
>  	 * thread address space:
> diff --git a/arch/sh/include/asm/thread_info.h b/arch/sh/include/asm/thread_info.h
> index ad27ffa..682a466 100644
> --- a/arch/sh/include/asm/thread_info.h
> +++ b/arch/sh/include/asm/thread_info.h
> @@ -32,6 +32,7 @@ struct thread_info {
>  	__u32			status;		/* thread synchronous flags */
>  	__u32			cpu;
>  	int			preempt_count; /* 0 => preemptable, <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	mm_segment_t		addr_limit;	/* thread address space */
>  	struct restart_block	restart_block;
>  	unsigned long		previous_sp;	/* sp of previous stack in case
> diff --git a/arch/sparc/include/asm/thread_info_32.h b/arch/sparc/include/asm/thread_info_32.h
> index 025c984..3dc0054 100644
> --- a/arch/sparc/include/asm/thread_info_32.h
> +++ b/arch/sparc/include/asm/thread_info_32.h
> @@ -32,6 +32,7 @@ struct thread_info {
>  	int			cpu;		/* cpu we're on */
>  	int			preempt_count;	/* 0 => preemptable,
>  						   <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	int			softirq_count;
>  	int			hardirq_count;
> 
> @@ -94,15 +95,16 @@ register struct thread_info *current_thread_info_reg asm("g6");
>  #define TI_FLAGS	0x0c
>  #define TI_CPU		0x10
>  #define TI_PREEMPT	0x14	/* preempt_count */
> -#define TI_SOFTIRQ	0x18	/* softirq_count */
> -#define TI_HARDIRQ	0x1c	/* hardirq_count */
> -#define TI_KSP		0x20	/* ksp */
> -#define TI_KPC		0x24	/* kpc (ldd'ed with kpc) */
> -#define TI_KPSR		0x28	/* kpsr */
> -#define TI_KWIM		0x2c	/* kwim (ldd'ed with kpsr) */
> -#define TI_REG_WINDOW	0x30
> -#define TI_RWIN_SPTRS	0x230
> -#define TI_W_SAVED	0x250
> +/* #define TI_PAGEFAULT	0x18 */ /* pagefault_count */
> +#define TI_SOFTIRQ	0x1c	/* softirq_count */
> +#define TI_HARDIRQ	0x20	/* hardirq_count */
> +#define TI_KSP		0x24	/* ksp */
> +#define TI_KPC		0x28	/* kpc (ldd'ed with kpc) */
> +#define TI_KPSR		0x2c	/* kpsr */
> +#define TI_KWIM		0x30	/* kwim (ldd'ed with kpsr) */
> +#define TI_REG_WINDOW	0x34
> +#define TI_RWIN_SPTRS	0x234
> +#define TI_W_SAVED	0x254
>  /* #define TI_RESTART_BLOCK 0x25n */ /* Nobody cares */
> 
>  /*
> diff --git a/arch/sparc/include/asm/thread_info_64.h b/arch/sparc/include/asm/thread_info_64.h
> index 798f027..4b54608 100644
> --- a/arch/sparc/include/asm/thread_info_64.h
> +++ b/arch/sparc/include/asm/thread_info_64.h
> @@ -50,6 +50,7 @@ struct thread_info {
>  	__u8			current_ds;
>  	__u16			cpu;
> 
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	unsigned long		*utraps;
> 
>  	struct reg_window 	reg_window[NSWINS];
> @@ -87,14 +88,14 @@ struct thread_info {
>  #define TI_NEW_CHILD	0x0000003c
>  #define TI_CURRENT_DS	0x0000003d
>  #define TI_CPU		0x0000003e
> -#define TI_UTRAPS	0x00000040
> -#define TI_REG_WINDOW	0x00000048
> -#define TI_RWIN_SPTRS	0x000003c8
> -#define TI_GSR		0x00000400
> -#define TI_XFSR		0x00000438
> -#define TI_RESTART_BLOCK 0x00000470
> -#define TI_KUNA_REGS	0x000004a0
> -#define TI_KUNA_INSN	0x000004a8
> +#define TI_UTRAPS	0x00000048
> +#define TI_REG_WINDOW	0x00000050
> +#define TI_RWIN_SPTRS	0x000003d0
> +#define TI_GSR		0x00000408
> +#define TI_XFSR		0x00000440
> +#define TI_RESTART_BLOCK 0x00000478
> +#define TI_KUNA_REGS	0x000004a8
> +#define TI_KUNA_INSN	0x000004b0
>  #define TI_FPREGS	0x000004c0
> 
>  /* We embed this in the uppermost byte of thread_info->flags */
> diff --git a/arch/tile/include/asm/thread_info.h b/arch/tile/include/asm/thread_info.h
> index 48e4fd0..57032b6 100644
> --- a/arch/tile/include/asm/thread_info.h
> +++ b/arch/tile/include/asm/thread_info.h
> @@ -33,6 +33,7 @@ struct thread_info {
>  	__u32			cpu;		/* current CPU */
>  	int			preempt_count;	/* 0 => preemptable,
>  						   <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
> 
>  	mm_segment_t		addr_limit;	/* thread address space
>  						   (KERNEL_DS or USER_DS) */
> diff --git a/arch/um/include/asm/thread_info.h b/arch/um/include/asm/thread_info.h
> index 1c5b2a8..90b193c 100644
> --- a/arch/um/include/asm/thread_info.h
> +++ b/arch/um/include/asm/thread_info.h
> @@ -19,6 +19,7 @@ struct thread_info {
>  	__u32			cpu;		/* current CPU */
>  	int			preempt_count;  /* 0 => preemptable,
>  						   <0 => BUG */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	mm_segment_t		addr_limit;	/* thread address space:
>  					 	   0-0xBFFFFFFF for user
>  						   0-0xFFFFFFFF for kernel */
> diff --git a/arch/unicore32/include/asm/thread_info.h b/arch/unicore32/include/asm/thread_info.h
> index af36d8e..1d50fb3 100644
> --- a/arch/unicore32/include/asm/thread_info.h
> +++ b/arch/unicore32/include/asm/thread_info.h
> @@ -69,6 +69,7 @@ struct thread_info {
>  	unsigned long		flags;		/* low level flags */
>  	int			preempt_count;	/* 0 => preemptable */
>  						/* <0 => bug */
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	mm_segment_t		addr_limit;	/* address limit */
>  	struct task_struct	*task;		/* main task structure */
>  	struct exec_domain	*exec_domain;	/* execution domain */
> diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
> index 547e344..fa075ab 100644
> --- a/arch/x86/include/asm/thread_info.h
> +++ b/arch/x86/include/asm/thread_info.h
> @@ -30,6 +30,7 @@ struct thread_info {
>  	__u32			status;		/* thread synchronous flags */
>  	__u32			cpu;		/* current CPU */
>  	int			saved_preempt_count;
> +	int			pagefault_count;/* pagefault_disable() levels */
>  	mm_segment_t		addr_limit;
>  	struct restart_block    restart_block;
>  	void __user		*sysenter_return;
> diff --git a/arch/xtensa/include/asm/thread_info.h b/arch/xtensa/include/asm/thread_info.h
> index 470153e..079e175 100644
> --- a/arch/xtensa/include/asm/thread_info.h
> +++ b/arch/xtensa/include/asm/thread_info.h
> @@ -49,6 +49,7 @@ struct thread_info {
>  	unsigned long		status;		/* thread-synchronous flags */
>  	__u32			cpu;		/* current CPU */
>  	__s32			preempt_count;	/* 0 => preemptable,< 0 => BUG*/
> +	__s32			pagefault_count;/* pagefault_disable() levels */
> 
>  	mm_segment_t		addr_limit;	/* thread address space */
>  	struct restart_block    restart_block;
> @@ -71,8 +72,8 @@ struct thread_info {
>  #define TI_STATUS	 0x0000000C
>  #define TI_CPU		 0x00000010
>  #define TI_PRE_COUNT	 0x00000014
> -#define TI_ADDR_LIMIT	 0x00000018
> -#define TI_RESTART_BLOCK 0x000001C
> +#define TI_ADDR_LIMIT	 0x0000001c
> +#define TI_RESTART_BLOCK 0x00000020
> 
>  #endif
> 

Re: [PATCH v1 1/5] uaccess: add pagefault_count to thread_info

[David Hildenbrand]

> Am 05.12.2014 um 12:18 schrieb David Hildenbrand:
> > This patch adds the pagefault_count to the thread_info of all
> > architectures. It will be used to count the pagefault_disable() levels
> > on a per-thread basis.
> > 
> > We are not reusing the preempt_count as this is per cpu on x86 and we want to
> > demangle pagefault_disable() from preemption in the future.
> > 
> > Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
> > ---
> >  arch/alpha/include/asm/thread_info.h      |  1 +
> >  arch/arc/include/asm/thread_info.h        |  1 +
> >  arch/arm/include/asm/thread_info.h        |  1 +
> >  arch/arm64/include/asm/thread_info.h      |  1 +
> >  arch/avr32/include/asm/thread_info.h      |  1 +
> >  arch/blackfin/include/asm/thread_info.h   |  1 +
> >  arch/c6x/include/asm/thread_info.h        |  1 +
> >  arch/cris/include/asm/thread_info.h       |  1 +
> >  arch/frv/include/asm/thread_info.h        |  1 +
> >  arch/hexagon/include/asm/thread_info.h    |  1 +
> >  arch/ia64/include/asm/thread_info.h       |  1 +
> >  arch/m32r/include/asm/thread_info.h       |  5 +++--
> >  arch/m68k/include/asm/thread_info.h       |  1 +
> >  arch/metag/include/asm/thread_info.h      |  1 +
> >  arch/microblaze/include/asm/thread_info.h |  1 +
> >  arch/mips/include/asm/thread_info.h       |  1 +
> >  arch/mn10300/include/asm/thread_info.h    |  1 +
> >  arch/openrisc/include/asm/thread_info.h   |  1 +
> >  arch/parisc/include/asm/thread_info.h     |  1 +
> >  arch/powerpc/include/asm/thread_info.h    |  1 +
> >  arch/s390/include/asm/thread_info.h       |  1 +
> >  arch/score/include/asm/thread_info.h      |  1 +
> >  arch/sh/include/asm/thread_info.h         |  1 +
> >  arch/sparc/include/asm/thread_info_32.h   | 20 +++++++++++---------
> >  arch/sparc/include/asm/thread_info_64.h   | 17 +++++++++--------
> 
> Maybe its easier to put the pagefault count at the end of the thread_info struct to make the patch smaller and easier to review for thoses architectures that have hand-maintained asm offsets? 

Jap, that's also what I asked for in my cover letter.

Right now I wanted to keep the new count close to the preempt_count and similar
on all archs.

So move it only on the "hand-maintained asm offset" archs or on all archs?

David