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Date:   Thu, 30 Aug 2018 19:15:10 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Eugeniy Paltsev <Eugeniy.Paltsev@synopsys.com>
Cc:     "mingo@kernel.org" <mingo@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Alexey.Brodkin@synopsys.com" <Alexey.Brodkin@synopsys.com>,
        "Vineet.Gupta1@synopsys.com" <Vineet.Gupta1@synopsys.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "linux-snps-arc@lists.infradead.org" 
        <linux-snps-arc@lists.infradead.org>,
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        "will.deacon@arm.com" <will.deacon@arm.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>
Subject: 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.