On Wed, May 21, 2014 at 10:34:44PM -0400, Sasha Levin wrote: > 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?
We do all that with preemption enabled, because its big and expensive, so its entirely possible that current (env->p) got moved around while we were doing it, at which point we'll look at it as a possible dst, while its already our src.
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