Messages in this thread | | | From | Kirill Tkhai <> | Subject | Re: sched: hang in migrate_swap | Date | Wed, 14 May 2014 14:21:04 +0400 |
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14.05.2014, 14:14, "Peter Zijlstra" <peterz@infradead.org>: > On Wed, May 14, 2014 at 01:42:32PM +0400, Kirill Tkhai wrote: > >> Peter, do we have to queue stop works orderly? >> >> Is there is not a possibility, when two pair of works queued different on >> different cpus? >> >> kernel/stop_machine.c | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c >> index b6b67ec..29e221b 100644 >> --- a/kernel/stop_machine.c >> +++ b/kernel/stop_machine.c >> @@ -250,8 +250,14 @@ struct irq_cpu_stop_queue_work_info { >> static void irq_cpu_stop_queue_work(void *arg) >> { >> struct irq_cpu_stop_queue_work_info *info = arg; >> - cpu_stop_queue_work(info->cpu1, info->work1); >> - cpu_stop_queue_work(info->cpu2, info->work2); >> + >> + if (info->cpu1 < info->cpu2) { >> + cpu_stop_queue_work(info->cpu1, info->work1); >> + cpu_stop_queue_work(info->cpu2, info->work2); >> + } else { >> + cpu_stop_queue_work(info->cpu2, info->work2); >> + cpu_stop_queue_work(info->cpu1, info->work1); >> + } >> } > > I'm not sure, we already send the IPI to the first cpu of the pair, so > supposing we have 4 cpus, and get 4 pairs like: > > 0,1 1,2 2,3 3,0 > > That would result in IPIs to 0, 1, 2, and 0 again, and since the IPI > function is serialized I don't immediately see a way for this to > deadlock.
It's about stop_two_cpus(), I have a distrust about other users of stop task:
queue_stop_cpus_work() queues work consequentially:
0 1 2 4
stop_two_cpus() may queue:
1 0
Looks like, stop thread on 0th and on 1th are waiting for wrong works. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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