Commit 96b3d28b authored Mar 06, 2014 by Fernando Luis Vazquez Cao Committed by Ingo Molnar Mar 11, 2014

sched/clock: Prevent tracing recursion in sched_clock_cpu()



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 95ef1e52
("KVM guest: prevent tracing recursion with kvmclock").

Signed-off-by: Fernando Luis Vazquez Cao <fernando@oss.ntt.co.jp>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1394083528.4524.3.camel@nexus


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 177c53d9

kernel/sched/clock.c

+2 −2

Original line number	Original line	Diff line number	Diff line
	@@ -301,14 +301,14 @@ u64 sched_clock_cpu(int cpu)
	if (unlikely(!sched_clock_running))		if (unlikely(!sched_clock_running))
	return 0ull;		return 0ull;

	preempt_disable();		preempt_disable_notrace();
	scd = cpu_sdc(cpu);		scd = cpu_sdc(cpu);

	if (cpu != smp_processor_id())		if (cpu != smp_processor_id())
	clock = sched_clock_remote(scd);		clock = sched_clock_remote(scd);
	else		else
	clock = sched_clock_local(scd);		clock = sched_clock_local(scd);
	preempt_enable();		preempt_enable_notrace();

	return clock;		return clock;
	}		}