linux-kernel - [tip:perf/core] kprobes/x86: Remove IRQ disabling from ftrace-based/optimized kprobes

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Date:   Thu, 28 Sep 2017 03:54:33 -0700
From:   tip-bot for Masami Hiramatsu <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     ast@...com, mhiramat@...nel.org, linux-kernel@...r.kernel.org,
        rostedt@...dmis.org, peterz@...radead.org, ast@...nel.org,
        ananth@...ux.vnet.ibm.com, hpa@...or.com, mingo@...nel.org,
        paulmck@...ux.vnet.ibm.com, torvalds@...ux-foundation.org,
        tglx@...utronix.de
Subject: [tip:perf/core] kprobes/x86: Remove IRQ disabling from
 ftrace-based/optimized kprobes

Commit-ID:  a19b2e3d783964d48d2b494439648e929bcdc976
Gitweb:     https://git.kernel.org/tip/a19b2e3d783964d48d2b494439648e929bcdc976
Author:     Masami Hiramatsu <mhiramat@...nel.org>
AuthorDate: Tue, 19 Sep 2017 19:02:20 +0900
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 28 Sep 2017 09:25:50 +0200

kprobes/x86: Remove IRQ disabling from ftrace-based/optimized kprobes

Kkprobes don't need to disable IRQs if they are called from the
ftrace/jump trampoline code, because Documentation/kprobes.txt says:

  -----
  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).
  -----

So let's remove IRQ disabling from those handlers.

Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Alexei Starovoitov <ast@...com>
Cc: Alexei Starovoitov <ast@...nel.org>
Cc: Ananth N Mavinakayanahalli <ananth@...ux.vnet.ibm.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Paul E . McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/150581534039.32348.11331736206004264553.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/kprobes/ftrace.c | 9 ++-------
 arch/x86/kernel/kprobes/opt.c    | 4 ----
 2 files changed, 2 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index bcfee4f..8dc0161 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -61,14 +61,11 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 {
 	struct kprobe *p;
 	struct kprobe_ctlblk *kcb;
-	unsigned long flags;
-
-	/* Disable irq for emulating a breakpoint and avoiding preempt */
-	local_irq_save(flags);
 
+	/* Preempt is disabled by ftrace */
 	p = get_kprobe((kprobe_opcode_t *)ip);
 	if (unlikely(!p) || kprobe_disabled(p))
-		goto end;
+		return;
 
 	kcb = get_kprobe_ctlblk();
 	if (kprobe_running()) {
@@ -91,8 +88,6 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
 		 * resets current kprobe, and keep preempt count +1.
 		 */
 	}
-end:
-	local_irq_restore(flags);
 }
 NOKPROBE_SYMBOL(kprobe_ftrace_handler);
 
diff --git a/arch/x86/kernel/kprobes/opt.c b/arch/x86/kernel/kprobes/opt.c
index 32c35cb..e941136 100644
--- a/arch/x86/kernel/kprobes/opt.c
+++ b/arch/x86/kernel/kprobes/opt.c
@@ -154,13 +154,10 @@ STACK_FRAME_NON_STANDARD(optprobe_template_func);
 static void
 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 {
-	unsigned long flags;
-
 	/* This is possible if op is under delayed unoptimizing */
 	if (kprobe_disabled(&op->kp))
 		return;
 
-	local_irq_save(flags);
 	preempt_disable();
 	if (kprobe_running()) {
 		kprobes_inc_nmissed_count(&op->kp);
@@ -182,7 +179,6 @@ optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
 		__this_cpu_write(current_kprobe, NULL);
 	}
 	preempt_enable_no_resched();
-	local_irq_restore(flags);
 }
 NOKPROBE_SYMBOL(optimized_callback);