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Date: Thu, 30 Aug 2018 14:46:16 +0000 From: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com> To: "peterz@...radead.org" <peterz@...radead.org>, "Eugeniy.Paltsev@...opsys.com" <Eugeniy.Paltsev@...opsys.com> CC: "mingo@...nel.org" <mingo@...nel.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Alexey.Brodkin@...opsys.com" <Alexey.Brodkin@...opsys.com>, "Vineet.Gupta1@...opsys.com" <Vineet.Gupta1@...opsys.com>, "tglx@...utronix.de" <tglx@...utronix.de>, "linux-snps-arc@...ts.infradead.org" <linux-snps-arc@...ts.infradead.org>, "yamada.masahiro@...ionext.com" <yamada.masahiro@...ionext.com>, "will.deacon@....com" <will.deacon@....com>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org> Subject: Re: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash 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. I'll test it with last Will fix. > If that doesn't cure things, then we've been looking in entirely the > wrong place. > > --- > diff --git a/include/asm-generic/bitops/lock.h b/include/asm-generic/bitops/lock.h > index 3ae021368f48..79c6978152f8 100644 > --- a/include/asm-generic/bitops/lock.h > +++ b/include/asm-generic/bitops/lock.h > @@ -57,12 +57,7 @@ static inline void clear_bit_unlock(unsigned int nr, volatile unsigned long *p) > static inline void __clear_bit_unlock(unsigned int nr, > volatile unsigned long *p) > { > - unsigned long old; > - > - p += BIT_WORD(nr); > - old = READ_ONCE(*p); > - old &= ~BIT_MASK(nr); > - atomic_long_set_release((atomic_long_t *)p, old); > + clear_bit_unlock(nr, p); > } > > /** -- Eugeniy Paltsev
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