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SubjectRe: [PATCH] kthread: Prevent unpark race which puts threads on the wrong cpu
Dave,

On Tue, 9 Apr 2013, Dave Hansen wrote:

> Hey Thomas,
>
> I don't think the patch helped my case. Looks like the same BUG_ON().
>
> I accidentally booted with possible_cpus=10 instead of 160. I wasn't
> able to trigger this in that case, even repeatedly on/offlining them.
> But, once I booted with possible_cpus=160, it triggered in a jiffy.

Darn. We should have merged Paul McKenneys NR_CPUS=0 patch last year
and we would have avoided the whole shebang.

> > [ 161.551788] smpboot_thread_fn():
> > [ 161.551807] td->cpu: 132
> > [ 161.551808] smp_processor_id(): 121
> > [ 161.551811] comm: migration/%u
> > [ 161.551840] ------------[ cut here ]------------
> > [ 161.551939] kernel BUG at kernel/smpboot.c:149!

Any chance, that you get a trace for that?

Thanks,

tglx



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