linux-kernel - [PATCH, v2] kprobes, x86: Disable irq during optimized callback

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Date:	Wed, 11 May 2011 13:06:13 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	masami.hiramatsu.pt@...achi.com, linux-kernel@...r.kernel.org
Subject: [PATCH, v2] kprobes, x86: Disable irq during optimized callback

On Tue, May 10, 2011 at 01:44:18PM +0200, Ingo Molnar wrote:
> 
> * Jiri Olsa <jolsa@...hat.com> wrote:
> 
> > On Tue, May 10, 2011 at 12:40:19PM +0200, Ingo Molnar wrote:
> > > 
> > > * Jiri Olsa <jolsa@...hat.com> wrote:
> > > 
> > > > +	local_irq_save(flags);
> > > >  	preempt_disable();
> > > >  	if (kprobe_running()) {
> > > >  		kprobes_inc_nmissed_count(&op->kp);
> > > > @@ -1208,6 +1210,7 @@ static void __kprobes optimized_callback(struct optimized_kprobe *op,
> > > >  		__this_cpu_write(current_kprobe, NULL);
> > > >  	}
> > > >  	preempt_enable_no_resched();
> > > > +	local_irq_restore(flags);
> > > 
> > > irq-disable is synonymous to preempt disable so the preempt_disable()/enable() 
> > > pair looks like superfluous overhead.
> > 
> > yes, there's correct patch already in the list here:
> > http://marc.info/?l=linux-kernel&m=130382756829695&w=2
> 
> It helps to change the subject line when you think another patch should be 
> considered, to something like:
> 
>   [PATCH, v2] kprobes, x86: Disable irq during optimized callback
> 
> (also note the other changes i made to the title, 3 altogether.)

sorry, here it is ;) thanks

jirka

---
Disabling irqs during optimized callback, so we dont miss
any in-irq kprobes as missed.

running following:

# cd /debug/tracing/
# echo "p mutex_unlock" >> kprobe_events
# echo "p _raw_spin_lock" >> kprobe_events
# echo "p smp_apic_timer_interrupt" >> ./kprobe_events
# echo 1 > events/enable

makes the optimized kprobes to be missed. None is missed
if the kprobe optimatization is disabled.


Signed-off-by: Jiri Olsa <jolsa@...hat.com>
---
 arch/x86/kernel/kprobes.c |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index c969fd9..f1a6244 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -1183,12 +1183,13 @@ static void __kprobes optimized_callback(struct optimized_kprobe *op,
 					 struct pt_regs *regs)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
+	unsigned long flags;
 
 	/* This is possible if op is under delayed unoptimizing */
 	if (kprobe_disabled(&op->kp))
 		return;
 
-	preempt_disable();
+	local_irq_save(flags);
 	if (kprobe_running()) {
 		kprobes_inc_nmissed_count(&op->kp);
 	} else {
@@ -1207,7 +1208,7 @@ static void __kprobes optimized_callback(struct optimized_kprobe *op,
 		opt_pre_handler(&op->kp, regs);
 		__this_cpu_write(current_kprobe, NULL);
 	}
-	preempt_enable_no_resched();
+	local_irq_restore(flags);
 }
 
 static int __kprobes copy_optimized_instructions(u8 *dest, u8 *src)
-- 
1.7.1

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