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Date: Thu, 30 Aug 2018 11:44:11 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Vineet Gupta <Vineet.Gupta1@...opsys.com> Cc: Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "will.deacon@....com" <will.deacon@....com>, "mingo@...nel.org" <mingo@...nel.org>, "tglx@...utronix.de" <tglx@...utronix.de>, "linux-snps-arc@...ts.infradead.org" <linux-snps-arc@...ts.infradead.org>, Alexey Brodkin <Alexey.Brodkin@...opsys.com>, "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 Wed, Aug 29, 2018 at 09:16:43PM +0000, Vineet Gupta wrote: > On 08/29/2018 11:33 AM, Eugeniy Paltsev wrote: > > Hi Guys, > > Since v4.19-rc1 we are getting a serious regression on platforms with ARC architecture. > > The kernel have become unstable and spontaneously crashes on LTP tests execution / IO tests or > > even on boot. > > > > I don't know exactly what breaks but bisect clearly assign the blame to this commit: > > 84c6591103db ("locking/atomics, asm-generic/bitops/lock.h: Rewrite using atomic_fetch_*()") > > https://github.com/torvalds/linux/commit/84c6591103dbeaf393a092a3fc7b09510825f6b9 > > > > Reverting the commit solves this problem. > > > > I tested v4.19-rc1 on ARM (wandboard, i.mx6, 32bit, quard core, ARMv7) which uses same > > generic bitops implementation and it works fine. > > > > Do you have any ideas what went wrong? > > Back in 2016, Peter had fixed this file due to a problem I reported on ARC. See > commit f75d48644c56a ("bitops: Do not default to __clear_bit() for > __clear_bit_unlock()") > That made __clear_bit_unlock() use the atomic clear_bit() vs. non-atomic > __clear_bit(), effectively making clear_bit_unlock() and __clear_bit_unlock() same. > > This patch undoes that which could explain the issues you see. @Peter, @Will ? Right, so the thinking is that on platforms that suffer that issue, atomic_set*() should DTRT. And if you look at your spinlock based atomic implementation, you'll note that atomic_set() does indeed do the right thing. arch/arc/include/asm/atomic.h:108
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