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From: Masami Hiramatsu <mhiramat@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>
Cc: x86@kernel.org, Masami Hiramatsu <mhiramat@kernel.org>,
	Ingo Molnar <mingo@redhat.com>, "H . Peter Anvin" <hpa@zytor.com>,
	linux-kernel@vger.kernel.org,
	Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Laura Abbott <labbott@redhat.com>, Josef Bacik <jbacik@fb.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Subject: [PATCH -tip v3 7/7] x86: kprobes: Do not disable preempt on int3 path
Date: Thu, 17 May 2018 09:00:03 +0900	[thread overview]
Message-ID: <152651520340.25583.15074431112097053694.stgit@devbox> (raw)
In-Reply-To: <152651499561.25583.14488389770693278906.stgit@devbox>

Since int3 and debug exception(for singlestep) are run with
IRQ disabled and while running single stepping we drop IF
from regs->flags, that path must not be preemptible. So we
can remove the preempt disable/enable calls from that path.

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Ingo Molnar <mingo@kernel.org>
---
 Changes in v3:
  - Split user-side changes to another patch
 Changes in v2:
  - Include user-side changes.
---
 Documentation/kprobes.txt      |   11 +++++------
 arch/x86/kernel/kprobes/core.c |   18 ++++--------------
 arch/x86/kernel/kprobes/opt.c  |    1 -
 3 files changed, 9 insertions(+), 21 deletions(-)

diff --git a/Documentation/kprobes.txt b/Documentation/kprobes.txt
index 907a3017c0f2..3e9e99ea751b 100644
--- a/Documentation/kprobes.txt
+++ b/Documentation/kprobes.txt
@@ -566,12 +566,11 @@ the same handler) may run concurrently on different CPUs.
 Kprobes does not use mutexes or allocate memory except during
 registration and unregistration.
 
-Probe handlers are run with preemption disabled.  Depending on the
-architecture and optimization state, handlers may also run with
-interrupts disabled (e.g., kretprobe handlers and optimized kprobe
-handlers run without interrupt disabled on x86/x86-64).  In any case,
-your handler should not yield the CPU (e.g., by attempting to acquire
-a semaphore).
+Probe handlers are run with preemption disabled or interrupt disabled,
+which depends on the architecture and optimization state.  (e.g.,
+kretprobe handlers and optimized kprobe handlers run without interrupt
+disabled on x86/x86-64).  In any case, your handler should not yield
+the CPU (e.g., by attempting to acquire a semaphore, or waiting I/O).
 
 Since a return probe is implemented by replacing the return
 address with the trampoline's address, stack backtraces and calls
diff --git a/arch/x86/kernel/kprobes/core.c b/arch/x86/kernel/kprobes/core.c
index 215a28bdd9df..a2896ff47ebc 100644
--- a/arch/x86/kernel/kprobes/core.c
+++ b/arch/x86/kernel/kprobes/core.c
@@ -596,7 +596,6 @@ static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
 		 * stepping.
 		 */
 		regs->ip = (unsigned long)p->ainsn.insn;
-		preempt_enable_no_resched();
 		return;
 	}
 #endif
@@ -669,12 +668,10 @@ int kprobe_int3_handler(struct pt_regs *regs)
 
 	addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
 	/*
-	 * We don't want to be preempted for the entire
-	 * duration of kprobe processing. We conditionally
-	 * re-enable preemption at the end of this function,
-	 * and also in reenter_kprobe() and setup_singlestep().
+	 * We don't want to be preempted for the entire duration of kprobe
+	 * processing. Since int3 and debug trap disables irqs and we clear
+	 * IF while singlestepping, it must be no preemptible.
 	 */
-	preempt_disable();
 
 	kcb = get_kprobe_ctlblk();
 	p = get_kprobe(addr);
@@ -695,10 +692,8 @@ int kprobe_int3_handler(struct pt_regs *regs)
 			 */
 			if (!p->pre_handler || !p->pre_handler(p, regs))
 				setup_singlestep(p, regs, kcb, 0);
-			else {
+			else
 				reset_current_kprobe();
-				preempt_enable_no_resched();
-			}
 			return 1;
 		}
 	} else if (*addr != BREAKPOINT_INSTRUCTION) {
@@ -712,11 +707,9 @@ int kprobe_int3_handler(struct pt_regs *regs)
 		 * the original instruction.
 		 */
 		regs->ip = (unsigned long)addr;
-		preempt_enable_no_resched();
 		return 1;
 	} /* else: not a kprobe fault; let the kernel handle it */
 
-	preempt_enable_no_resched();
 	return 0;
 }
 NOKPROBE_SYMBOL(kprobe_int3_handler);
@@ -967,8 +960,6 @@ int kprobe_debug_handler(struct pt_regs *regs)
 	}
 	reset_current_kprobe();
 out:
-	preempt_enable_no_resched();
-
 	/*
 	 * if somebody else is singlestepping across a probe point, flags
 	 * will have TF set, in which case, continue the remaining processing
@@ -1015,7 +1006,6 @@ int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 			restore_previous_kprobe(kcb);
 		else
 			reset_current_kprobe();
-		preempt_enable_no_resched();
 	} else if (kcb->kprobe_status == KPROBE_HIT_ACTIVE ||
 		   kcb->kprobe_status == KPROBE_HIT_SSDONE) {
 		/*
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 203d398802a3..eaf02f2e7300 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -491,7 +491,6 @@ int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
 		regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
 		if (!reenter)
 			reset_current_kprobe();
-		preempt_enable_no_resched();
 		return 1;
 	}
 	return 0;

  parent reply	other threads:[~2018-05-17  0:00 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-16 23:56 [PATCH -tip v3 0/7] kprobes: x86: Cleanup jprobe implementation on x86 Masami Hiramatsu
2018-05-16 23:57 ` [PATCH -tip v3 1/7] Documentation/kprobes: Fix to remove remaining jprobe Masami Hiramatsu
2018-05-16 23:57 ` [PATCH -tip v3 2/7] kprobes: Remove jprobe API implementation Masami Hiramatsu
2018-05-16 23:58 ` [PATCH -tip v3 3/7] x86: kprobes: Remove jprobe implementation Masami Hiramatsu
2018-05-16 23:58 ` [PATCH -tip v3 4/7] kprobes: Ignore break_handler Masami Hiramatsu
2018-05-18  6:16   ` Ingo Molnar
2018-05-18 13:38     ` Masami Hiramatsu
2018-05-18  6:20   ` Ingo Molnar
2018-05-18 14:14     ` Masami Hiramatsu
2018-05-16 23:59 ` [PATCH -tip v3 5/7] x86: " Masami Hiramatsu
2018-05-18  6:26   ` Ingo Molnar
2018-05-18 13:42     ` Masami Hiramatsu
2018-05-16 23:59 ` [PATCH -tip v3 6/7] bpf: error-inject: x86: Fix unbalanced preempt-count for function override Masami Hiramatsu
2018-05-17  0:00 ` Masami Hiramatsu [this message]
2018-05-18  6:23 ` [PATCH -tip v3 0/7] kprobes: x86: Cleanup jprobe implementation on x86 Ingo Molnar
2018-05-18 14:10   ` Masami Hiramatsu

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