Re: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash

From: Peter Zijlstra
Date: Thu Aug 30 2018 - 13:15:20 EST

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In reply to: Eugeniy Paltsev: "Re: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash"
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On Thu, Aug 30, 2018 at 02:46:16PM +0000, Eugeniy Paltsev wrote:
> On Thu, 2018-08-30 at 16:17 +0200, Peter Zijlstra wrote:
> > On Thu, Aug 30, 2018 at 11:53:17AM +0000, Eugeniy Paltsev wrote:
> > > I can see crashes with LLSC enabled in both SMP running on 4 cores
> > > and SMP running on 1 core.
> >
> > So you're running on LL/SC enabled hardware; that would make Will's
> > patch irrelevant (although still a good idea for the hardware that does
> > care about that spinlocked atomic crud).
> >
> > Does something like the below cure things? That would confirm the
> > suggestion that the change to __clear_bit_unlock() is the curprit.
>
> I tested it - this doesn't change anything, the problem still reproduces.

OK, 'good' :-)

> I'll test it with last Will fix.

Yes, that missing "bnz 1b" is very very suspect.