Re: sched: spinlock recursion in migrate_swap_stop

From: Sasha Levin
Date: Wed May 21 2014 - 22:35:27 EST


On 05/21/2014 12:49 PM, Peter Zijlstra wrote:
> On Wed, May 21, 2014 at 03:19:48PM +0200, Peter Zijlstra wrote:
>> > On Wed, May 21, 2014 at 09:08:26AM -0400, Sasha Levin wrote:
>>> > > +++ b/kernel/sched/core.c
>>> > > @@ -1154,6 +1156,7 @@ int migrate_swap(struct task_struct *cur, struct task_struct *p)
>>> > > goto out;
>>> > >
>>> > > trace_sched_swap_numa(cur, arg.src_cpu, p, arg.dst_cpu);
>>> > > + BUG_ON(cur == p);
>>> > > ret = stop_two_cpus(arg.dst_cpu, arg.src_cpu, migrate_swap_stop, &arg);
>>> > >
>>> > > out:
>>> > >
>>> > >
>>> > > Which seems to get hit. This sounds like a race with task moving to
>>> > > other cpu maybe?
>> >
>> > Oi, good call that, lemme go stare.
> I think something simple like this should be sufficient to avoid the
> problem of selecting oneself as a flip target.

Why would that happen in the first place?


Thanks,
Sasha
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