Re: softlockups in multi_cpu_stop

[Ming Lei]

On Sat, Mar 7, 2015 at 11:10 AM, Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote:
> On Sat, 2015-03-07 at 10:55 +0800, Ming Lei wrote:
>> On Sat, Mar 7, 2015 at 10:29 AM, Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote:
>> > On Fri, 2015-03-06 at 18:26 -0800, Davidlohr Bueso wrote:
>> >> That's not what this is about. New lock _owners_ need to worry about
>> >                                                       ^^^ make that "need not"
>>
>> Sorry, could you explain a bit why new owner can't be scheduled
>> out(on_cpu becomes zero)? If that is possible, it still can cause
>> soft lockup like current problem.
>
> Oh its not that it can't be scheduled out. The point is we don't care
> what happens with the lock owner itself (new or not). We care about, and
> the point of this discussion, how _other_ threads handle themselves when
> trying to take that lock (a lock having an owner implies the lock is not
> free, of course). So if a lock owner gets scheduled out... so what?
> That's already taken into account by spinners.

Not exactly, current problem is just in spinner because it
ignores scheduled out owner and continues to spin, then
cause lockup, isn't it?

Thanks,
Ming Lei
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