From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eugeniy.Paltsev@synopsys.com (Eugeniy Paltsev) Date: Thu, 30 Aug 2018 14:46:16 +0000 Subject: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash In-Reply-To: <20180830141713.GN24082@hirez.programming.kicks-ass.net> References: <1535567633.4465.23.camel@synopsys.com> <20180830094411.GX24124@hirez.programming.kicks-ass.net> <20180830095148.GB5942@arm.com> <1535629996.4465.44.camel@synopsys.com> <20180830141713.GN24082@hirez.programming.kicks-ass.net> List-ID: Message-ID: <1535640375.4465.68.camel@synopsys.com> To: linux-snps-arc@lists.infradead.org On Thu, 2018-08-30@16:17 +0200, Peter Zijlstra wrote: > On Thu, Aug 30, 2018@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