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Date: Thu, 30 Aug 2018 16:17:13 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com> Cc: "will.deacon@....com" <will.deacon@....com>, "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>, "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, 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. 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); } /**
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