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authorDominik Dingel <dingel@linux.vnet.ibm.com>2015-09-18 11:27:45 +0200
committerPaolo Bonzini <pbonzini@redhat.com>2015-09-18 13:47:59 +0200
commit00cc1633816de8c95f337608a1ea64e228faf771 (patch)
treee2d7d478433a78a135df3aa575cfad98a34c950a /kernel
parentefe4d36a75d4dfd1a9c161b2bbf9b90beb4d9648 (diff)
downloadop-kernel-dev-00cc1633816de8c95f337608a1ea64e228faf771.zip
op-kernel-dev-00cc1633816de8c95f337608a1ea64e228faf771.tar.gz
sched: access local runqueue directly in single_task_running
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> Cc: <stable@vger.kernel.org> Fixes: 2ee507c472939db4b146d545352b8a7c79ef47f8 Signed-off-by: Dominik Dingel <dingel@linux.vnet.ibm.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/sched/core.c15
1 files changed, 11 insertions, 4 deletions
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 3595403..4064f79 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2666,13 +2666,20 @@ 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);
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