LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Marco Elver <elver@google.com>
To: elver@google.com
Cc: paulmck@kernel.org, andreyknvl@google.com, glider@google.com,
	dvyukov@google.com, kasan-dev@googlegroups.com,
	linux-kernel@vger.kernel.org, peterz@infradead.org,
	mingo@redhat.com, will@kernel.org, Qian Cai <cai@lca.pw>
Subject: [PATCH -rcu] kcsan: Make KCSAN compatible with lockdep
Date: Tue, 14 Jan 2020 13:49:19 +0100	[thread overview]
Message-ID: <20200114124919.11891-1-elver@google.com> (raw)

To avoid unexpected reentry into lockdep's IRQ tracing code via KCSAN
(if TRACE_IRQFLAGS is enabled), (1) use raw versions of
local_irq_{save,restore} in kcsan_setup_watchpoint(), and (2) disable
lockdep in kcsan_report() to avoid IRQ flags tracing upon generating the
report.

Tested with:

  CONFIG_LOCKDEP=y
  CONFIG_DEBUG_LOCKDEP=y

Where previously, the following warning (and variants with different
stack traces) was consistently generated, with the fix introduced in
this patch, the warning cannot be reproduced.

    WARNING: CPU: 0 PID: 2 at kernel/locking/lockdep.c:4406 check_flags.part.0+0x101/0x220
    Modules linked in:
    CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.5.0-rc1+ #11
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
    RIP: 0010:check_flags.part.0+0x101/0x220
    <snip>
    Call Trace:
     lock_is_held_type+0x69/0x150
     freezer_fork+0x20b/0x370
     cgroup_post_fork+0x2c9/0x5c0
     copy_process+0x2675/0x3b40
     _do_fork+0xbe/0xa30
     ? _raw_spin_unlock_irqrestore+0x40/0x50
     ? match_held_lock+0x56/0x250
     ? kthread_park+0xf0/0xf0
     kernel_thread+0xa6/0xd0
     ? kthread_park+0xf0/0xf0
     kthreadd+0x321/0x3d0
     ? kthread_create_on_cpu+0x130/0x130
     ret_from_fork+0x3a/0x50
    irq event stamp: 64
    hardirqs last  enabled at (63): [<ffffffff9a7995d0>] _raw_spin_unlock_irqrestore+0x40/0x50
    hardirqs last disabled at (64): [<ffffffff992a96d2>] kcsan_setup_watchpoint+0x92/0x460
    softirqs last  enabled at (32): [<ffffffff990489b8>] fpu__copy+0xe8/0x470
    softirqs last disabled at (30): [<ffffffff99048939>] fpu__copy+0x69/0x470

Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Marco Elver <elver@google.com>
---
 kernel/kcsan/core.c     |  4 ++--
 kernel/kcsan/report.c   | 11 +++++++++++
 kernel/locking/Makefile |  3 +++
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
index 87bf857c8893..e75f3dbf627e 100644
--- a/kernel/kcsan/core.c
+++ b/kernel/kcsan/core.c
@@ -337,7 +337,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
 	 *      detection point of view) to simply disable preemptions to ensure
 	 *      as many tasks as possible run on other CPUs.
 	 */
-	local_irq_save(irq_flags);
+	raw_local_irq_save(irq_flags);
 
 	watchpoint = insert_watchpoint((unsigned long)ptr, size, is_write);
 	if (watchpoint == NULL) {
@@ -429,7 +429,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type)
 
 	kcsan_counter_dec(KCSAN_COUNTER_USED_WATCHPOINTS);
 out_unlock:
-	local_irq_restore(irq_flags);
+	raw_local_irq_restore(irq_flags);
 out:
 	user_access_restore(ua_flags);
 }
diff --git a/kernel/kcsan/report.c b/kernel/kcsan/report.c
index b5b4feea49de..57ab7ef9786c 100644
--- a/kernel/kcsan/report.c
+++ b/kernel/kcsan/report.c
@@ -2,6 +2,7 @@
 
 #include <linux/jiffies.h>
 #include <linux/kernel.h>
+#include <linux/lockdep.h>
 #include <linux/preempt.h>
 #include <linux/printk.h>
 #include <linux/sched.h>
@@ -410,6 +411,14 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type,
 {
 	unsigned long flags = 0;
 
+	/*
+	 * With TRACE_IRQFLAGS, lockdep's internal IRQ flags state becomes
+	 * corrupted if we do not turn off lockdep. The likely cause is
+	 * unexpected reentry into IRQ tracing code via KCSAN if we detect a
+	 * data race.
+	 */
+	lockdep_off();
+
 	kcsan_disable_current();
 	if (prepare_report(&flags, ptr, size, access_type, cpu_id, type)) {
 		if (print_report(ptr, size, access_type, value_change, cpu_id, type) && panic_on_warn)
@@ -418,4 +427,6 @@ void kcsan_report(const volatile void *ptr, size_t size, int access_type,
 		release_report(&flags, type);
 	}
 	kcsan_enable_current();
+
+	lockdep_on();
 }
diff --git a/kernel/locking/Makefile b/kernel/locking/Makefile
index 45452facff3b..6d11cfb9b41f 100644
--- a/kernel/locking/Makefile
+++ b/kernel/locking/Makefile
@@ -5,6 +5,9 @@ KCOV_INSTRUMENT		:= n
 
 obj-y += mutex.o semaphore.o rwsem.o percpu-rwsem.o
 
+# Avoid recursion lockdep -> KCSAN -> ... -> lockdep.
+KCSAN_SANITIZE_lockdep.o := n
+
 ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_lockdep.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_lockdep_proc.o = $(CC_FLAGS_FTRACE)
-- 
2.25.0.rc1.283.g88dfdc4193-goog


             reply	other threads:[~2020-01-14 12:49 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-14 12:49 Marco Elver [this message]
2020-01-14 17:24 ` Alexander Potapenko
2020-01-15 16:26   ` Marco Elver
2020-01-15 16:37     ` Paul E. McKenney
2020-01-16  3:39       ` Qian Cai
2020-01-16  4:37         ` Qian Cai
2020-01-16 17:40           ` Paul E. McKenney
2020-01-16 17:50             ` Qian Cai
2020-01-16 17:55               ` Qian Cai
2020-01-16 18:57         ` Marco Elver
2020-01-17 16:40           ` Paul E. McKenney
2020-01-17 16:59             ` Qian Cai
2020-01-17 22:51               ` Marco Elver
2020-01-17 22:54             ` Marco Elver
2020-01-17 23:23               ` Paul E. McKenney

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200114124919.11891-1-elver@google.com \
    --to=elver@google.com \
    --cc=andreyknvl@google.com \
    --cc=cai@lca.pw \
    --cc=dvyukov@google.com \
    --cc=glider@google.com \
    --cc=kasan-dev@googlegroups.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=paulmck@kernel.org \
    --cc=peterz@infradead.org \
    --cc=will@kernel.org \
    --subject='Re: [PATCH -rcu] kcsan: Make KCSAN compatible with lockdep' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).