diff options
| author | Dominik Dingel <dingel@linux.vnet.ibm.com> | 2015-09-18 11:27:45 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-10-22 14:43:12 -0700 |
| commit | feada04ec6c916fa3779d736e75c8453ee3ddc58 (patch) | |
| tree | b5aae728533c673aab51aa2b943e7264b503853f /kernel | |
| parent | f829ccff84346019decac2a527495bbaa5565008 (diff) | |
sched: access local runqueue directly in single_task_running
commit 00cc1633816de8c95f337608a1ea64e228faf771 upstream.
Commit 2ee507c47293 ("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 f78195129963 ("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>
Fixes: 2ee507c472939db4b146d545352b8a7c79ef47f8
Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/core.c | 15 |
1 files changed, 11 insertions, 4 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e6910526c84b..4a42f8299ac8 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2358,13 +2358,20 @@ unsigned long nr_running(void) /* * 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) { - if (cpu_rq(smp_processor_id())->nr_running == 1) - return true; - else - return false; + return raw_rq()->nr_running == 1; } EXPORT_SYMBOL(single_task_running); |