Messages in this thread Patch in this message | | | From | Dominik Dingel <> | Subject | [PATCH] sched: access local runqueue directly in single_task_running | Date | Fri, 18 Sep 2015 11:27:45 +0200 |
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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> Cc: <stable@vger.kernel.org> # 4.2.x Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> --- kernel/sched/core.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 78b4bad10..5bfad0b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2614,13 +2614,13 @@ unsigned long nr_running(void) /* * Check if only the current task is running on the cpu. + * + * Caution result is subject to time-of-check-to-time-of-use race, + * every caller is responsible to set up additional fences if necessary. */ 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); -- 2.3.8
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