From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash Date: Thu, 30 Aug 2018 10:35:13 +0100 Message-ID: <20180830093513.GA5942@arm.com> References: <1535567633.4465.23.camel@synopsys.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Vineet Gupta Cc: Eugeniy Paltsev , "linux-kernel@vger.kernel.org" , "mingo@kernel.org" , "peterz@infradead.org" , "tglx@linutronix.de" , "linux-snps-arc@lists.infradead.org" , Alexey Brodkin , "yamada.masahiro@socionext.com" , "linux-arm-kernel@lists.infradead.org" , "linux-arch@vger.kernel.org" List-Id: linux-arch.vger.kernel.org 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 ? /me grabs arc toolchain (incidentally, make.cross fuzzy matches "arc" to "sparc", so that was fun for a few minutes). I'll take a look today, thanks for the report. Will From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.101.70]:38376 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727988AbeH3NgR (ORCPT ); Thu, 30 Aug 2018 09:36:17 -0400 Date: Thu, 30 Aug 2018 10:35:13 +0100 From: Will Deacon Subject: Re: Patch "asm-generic/bitops/lock.h: Rewrite using atomic_fetch_" causes kernel crash Message-ID: <20180830093513.GA5942@arm.com> References: <1535567633.4465.23.camel@synopsys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-arch-owner@vger.kernel.org List-ID: To: Vineet Gupta Cc: Eugeniy Paltsev , "linux-kernel@vger.kernel.org" , "mingo@kernel.org" , "peterz@infradead.org" , "tglx@linutronix.de" , "linux-snps-arc@lists.infradead.org" , Alexey Brodkin , "yamada.masahiro@socionext.com" , "linux-arm-kernel@lists.infradead.org" , "linux-arch@vger.kernel.org" Message-ID: <20180830093513.FSOOihH1_o-w3GfzpIHqCH7HjgmpCHpSrmjXe8JPaGo@z> 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 ? /me grabs arc toolchain (incidentally, make.cross fuzzy matches "arc" to "sparc", so that was fun for a few minutes). I'll take a look today, thanks for the report. Will