sched/clock: prevent tracing recursion in sched_clock_cpu()

From: Fernando Luis Vazquez Cao <[email protected]>

Prevent tracing of preempt_disable/enable() in sched_clock_cpu(). When CONFIG_DEBUG_PREEMPT is enabled, preempt_disable/enable() are traced and this causes trace_clock() users (and probably others) to go into an infinite recursion. Systems with a stable sched_clock() are not affected.

This problem is similar to that fixed by upstream commit 95ef1e52922 ("KVM guest: prevent tracing recursion with kvmclock").

Cc Linus Torvalds <[email protected]>

Cc Andrew Morton <[email protected]>

Cc Ingo Molnar <[email protected]>

Cc Steven Rostedt <[email protected]>

Signed-off-by Fernando Luis Vazquez Cao <[email protected]>

---

diff -urNp linux-3.14-rc5-orig/kernel/sched/clock.c linux-3.14-rc5/kernel/sched/clock.c

kernel/sched/clock.c +2 -2

@@ -301,14 +301,14 @@ u64 sched_clock_cpu(int cpu)
 	if (unlikely(!sched_clock_running))
 		return 0ull;
 
-	preempt_disable();
+	preempt_disable_notrace();
 	scd = cpu_sdc(cpu);
 
 	if (cpu != smp_processor_id())
 		clock = sched_clock_remote(scd);
 	else
 		clock = sched_clock_local(scd);
-	preempt_enable();
+	preempt_enable_notrace();
 
 	return clock;
 }

Quoted 8 lines · On Thu, 06 Mar 2014 14:25:28 +0900 Fernando Luis Vázquez Cao…

From: Fernando Luis Vazquez Cao <[email protected]>

Prevent tracing of preempt_disable/enable() in sched_clock_cpu(). When CONFIG_DEBUG_PREEMPT is enabled, preempt_disable/enable() are traced and this causes trace_clock() users (and probably others) to go into an infinite recursion. Systems with a stable sched_clock() are not affected.

Quoted 2 lines

This problem is similar to that fixed by upstream commit 95ef1e52922 ("KVM guest: prevent tracing recursion with kvmclock").

Also similar to: 569d6557ab957.

Acked-by Steven Rostedt <[email protected]>

Thank you four your review, Peter, Steven.

By the way, who is going to pick this patch? Do you want me to resend with Steven's Acked-by added?

Quoted 4 lines · On Mon, 10 Mar 2014 16:17:18 +0900 Fernando Luis Vázquez Cao…

Thank you four your review, Peter, Steven.

By the way, who is going to pick this patch? Do you want me to resend with Steven's Acked-by added?

I don't think you have to. I believe Peter got it. I know there's a bunch of patches he's trying to get pushed forward.

From: Fernando Luis Vazquez Cao <[email protected]>

Prevent tracing of preempt_disable/enable() in sched_clock_cpu(). When CONFIG_DEBUG_PREEMPT is enabled, preempt_disable/enable() are traced and this causes trace_clock() users (and probably others) to go into an infinite recursion. Systems with a stable sched_clock() are not affected.

This problem is similar to that fixed by upstream commit 95ef1e52922 ("KVM guest: prevent tracing recursion with kvmclock").

Cc Linus Torvalds <[email protected]>

Cc Andrew Morton <[email protected]>

Cc Ingo Molnar <[email protected]>

Cc Steven Rostedt <[email protected]>

Signed-off-by Fernando Luis Vazquez Cao <[email protected]>