From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752742AbaABUmg (ORCPT ); Thu, 2 Jan 2014 15:42:36 -0500 Received: from smtp.codeaurora.org ([198.145.11.231]:56640 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752682AbaABUme (ORCPT ); Thu, 2 Jan 2014 15:42:34 -0500 Message-ID: <52C5CF38.1010704@codeaurora.org> Date: Thu, 02 Jan 2014 12:42:32 -0800 From: Stephen Boyd User-Agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:24.0) Gecko/20100101 Thunderbird/24.1.1 MIME-Version: 1.0 To: John Stultz , Linus Torvalds , =?UTF-8?B?S3J6eXN6dG9mIEhhxYJhc2E=?= CC: =?UTF-8?B?VXdlIEtsZWluZS1Lw7ZuaWc=?= , Willy Tarreau , lkml , "linux-arm-kernel@lists.infradead.org" , Ingo Molnar Subject: Re: v3.13-rc6+ regression (ARM board) References: <20131231104511.GA9688@1wt.eu> <20140102101455.GG10158@pengutronix.de> <52C5C5F6.70803@linaro.org> <52C5CC54.4050602@linaro.org> In-Reply-To: <52C5CC54.4050602@linaro.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/02/14 12:30, John Stultz wrote: > On 01/02/2014 12:03 PM, John Stultz wrote: >> On 01/02/2014 11:38 AM, Linus Torvalds wrote: >>> On Thu, Jan 2, 2014 at 4:07 AM, Krzysztof Hałasa wrote: >>>> This means these two commits don't like each other: >>>> >>>> seqcount: Add lockdep functionality to seqcount/seqlock structures >>>> sched_clock: Use seqcount instead of rolling our own >>> Does something like this fix it for you? >>> >>> --- a/kernel/time/sched_clock.c >>> +++ b/kernel/time/sched_clock.c >>> @@ -36,6 +36,7 @@ core_param(irqtime, irqtime, int, 0400); >>> >>> static struct clock_data cd = { >>> .mult = NSEC_PER_SEC / HZ, >>> + .seq = SEQCNT_ZERO(cd.seq), >>> }; >>> >>> static u64 __read_mostly sched_clock_mask; >>> >>> (The above is not even compile-tested, because x86 doesn't use >>> GENERIC_SCHED_CLOCK. So I did the patch blindly, but I think you get >>> the idea..) >> Sheesh. Just finishing up holiday email backlog and Linus already has a >> fix. :) >> >> This looks like it should fix the issue, and does build for me. >> >> Assuming it works for Krzysztof, > So something else may be at play. Even with Linus' patch I reproduced a > similar hang here. > > Still chasing it down, but it looks like a seqlock deadlock where we're > calling read while holding the lock. > Do you have tracing enabled? When I moved this code over to use seqcounts it relied on the fact that the compiler wouldn't be generating any function calls to the tracing code. Before seqcounts got lockdep support it all collapsed down into sched_clock() due to the use of inline on the seqlock API. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation From mboxrd@z Thu Jan 1 00:00:00 1970 From: sboyd@codeaurora.org (Stephen Boyd) Date: Thu, 02 Jan 2014 12:42:32 -0800 Subject: v3.13-rc6+ regression (ARM board) In-Reply-To: <52C5CC54.4050602@linaro.org> References: <20131231104511.GA9688@1wt.eu> <20140102101455.GG10158@pengutronix.de> <52C5C5F6.70803@linaro.org> <52C5CC54.4050602@linaro.org> Message-ID: <52C5CF38.1010704@codeaurora.org> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 01/02/14 12:30, John Stultz wrote: > On 01/02/2014 12:03 PM, John Stultz wrote: >> On 01/02/2014 11:38 AM, Linus Torvalds wrote: >>> On Thu, Jan 2, 2014 at 4:07 AM, Krzysztof Ha?asa wrote: >>>> This means these two commits don't like each other: >>>> >>>> seqcount: Add lockdep functionality to seqcount/seqlock structures >>>> sched_clock: Use seqcount instead of rolling our own >>> Does something like this fix it for you? >>> >>> --- a/kernel/time/sched_clock.c >>> +++ b/kernel/time/sched_clock.c >>> @@ -36,6 +36,7 @@ core_param(irqtime, irqtime, int, 0400); >>> >>> static struct clock_data cd = { >>> .mult = NSEC_PER_SEC / HZ, >>> + .seq = SEQCNT_ZERO(cd.seq), >>> }; >>> >>> static u64 __read_mostly sched_clock_mask; >>> >>> (The above is not even compile-tested, because x86 doesn't use >>> GENERIC_SCHED_CLOCK. So I did the patch blindly, but I think you get >>> the idea..) >> Sheesh. Just finishing up holiday email backlog and Linus already has a >> fix. :) >> >> This looks like it should fix the issue, and does build for me. >> >> Assuming it works for Krzysztof, > So something else may be at play. Even with Linus' patch I reproduced a > similar hang here. > > Still chasing it down, but it looks like a seqlock deadlock where we're > calling read while holding the lock. > Do you have tracing enabled? When I moved this code over to use seqcounts it relied on the fact that the compiler wouldn't be generating any function calls to the tracing code. Before seqcounts got lockdep support it all collapsed down into sched_clock() due to the use of inline on the seqlock API. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation