Messages in this thread Patch in this message |  | | Date | Tue, 4 Oct 2016 01:06:56 -0700 | From | tip-bot for Ingo Molnar <> | Subject | [tip:sched/urgent] Revert "sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()" |
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Commit-ID: be6a2e4c46cc122ba9113ba569fbc50fad075fff Gitweb: http://git.kernel.org/tip/be6a2e4c46cc122ba9113ba569fbc50fad075fff Author: Ingo Molnar <mingo@kernel.org> AuthorDate: Tue, 4 Oct 2016 09:55:57 +0200 Committer: Ingo Molnar <mingo@kernel.org> CommitDate: Tue, 4 Oct 2016 09:55:57 +0200
Revert "sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()"
This reverts commit 4fa5cd5245b627db88c9ca08ae442373b02596b4.
The original change widens a preempt-off section, to avoid a seemingly unsafe smp_processor_id() use.
During review I overlooked two facts:
- The code to calls a non-trivial function callback:
ht->park(td->cpu);
... which might (and does occasionally) sleep, triggering the warning.
- More importantly, as pointed out by Peter Zijlstra, using smp_processor_id() in that context is safe, if it's done from a kernel thread that is pinned to a single CPU - which is the case here.
So revert to the original code that enables preemption sooner.
Reported-by: kernel test robot <xiaolong.ye@intel.com> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Con Kolivas <kernel@kolivas.org> Cc: Alfred Chen <cchalpha@gmail.com> Link: http://lkml.kernel.org/r/20160930015102.GB20189@yexl-desktop Signed-off-by: Ingo Molnar <mingo@kernel.org> --- kernel/smpboot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/smpboot.c b/kernel/smpboot.c index fc0d8270..13bc43d 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -122,12 +122,12 @@ static int smpboot_thread_fn(void *data) if (kthread_should_park()) { __set_current_state(TASK_RUNNING); + preempt_enable(); if (ht->park && td->status == HP_THREAD_ACTIVE) { BUG_ON(td->cpu != smp_processor_id()); ht->park(td->cpu); td->status = HP_THREAD_PARKED; } - preempt_enable(); kthread_parkme(); /* We might have been woken for stop */ continue;
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