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sched: access local runqueue directly in single_task_running 

Commit 2ee507c472 ("sched: Add function single_task_running to let a task
check if it is the only task running on a cpu") referenced the current
runqueue with the smp_processor_id.  When CONFIG_DEBUG_PREEMPT is enabled,
that is only allowed if preemption is disabled or the currrent task is
bound to the local cpu (e.g. kernel worker).

With commit f781951299 ("kvm: add halt_poll_ns module parameter") KVM
calls single_task_running. If CONFIG_DEBUG_PREEMPT is enabled that
generates a lot of kernel messages.

To avoid adding preemption in that cases, as it would limit the usefulness,
we change single_task_running to access directly the cpu local runqueue.

Cc: Tim Chen <tim.c.chen@linux.intel.com>
Suggested-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <stable@vger.kernel.org>
Fixes: 2ee507c472
Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Dominik Dingel 2015-09-18 11:27:45 +02:00 committed by Paolo Bonzini
parent efe4d36a75
commit 00cc163381
1 changed files with 11 additions and 4 deletions
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15
kernel/sched/core.c
View File

@ -2666,13 +2666,20 @@ unsigned long nr_running(void)
/* /*
* Check if only the current task is running on the cpu. * Check if only the current task is running on the cpu.
*
* Caution: this function does not check that the caller has disabled
* preemption, thus the result might have a time-of-check-to-time-of-use
* race. The caller is responsible to use it correctly, for example:
*
* - from a non-preemptable section (of course)
*
* - from a thread that is bound to a single CPU
*
* - in a loop with very short iterations (e.g. a polling loop)
*/ */
bool single_task_running(void) bool single_task_running(void)
{ {
if (cpu_rq(smp_processor_id())->nr_running == 1) return raw_rq()->nr_running == 1;
return true;
else
return false;
} }
EXPORT_SYMBOL(single_task_running); EXPORT_SYMBOL(single_task_running);