From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757534AbdDRRXR (ORCPT ); Tue, 18 Apr 2017 13:23:17 -0400 Received: from mail-qk0-f195.google.com ([209.85.220.195]:35243 "EHLO mail-qk0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753042AbdDRRXN (ORCPT ); Tue, 18 Apr 2017 13:23:13 -0400 Subject: Re: [PATCH linux-4.1.y] sched/wait: Fix signal handling in bit wait helpers To: Oleg Nesterov , alexander.levin@verizon.com References: <20170412180345.31339-1-f.fainelli@gmail.com> <20170418134631.GA13416@redhat.com> Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org, Peter Zijlstra , Linus Torvalds , Mike Galbraith , Thomas Gleixner , mark.rutland@arm.com, neilb@suse.de, Ingo Molnar From: Florian Fainelli Message-ID: <0a66edde-7573-d95f-f4bf-b0dc68ca2577@gmail.com> Date: Tue, 18 Apr 2017 10:23:08 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170418134631.GA13416@redhat.com> 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 04/18/2017 06:46 AM, Oleg Nesterov wrote: > Just curious, any particular reason you want to backport this patch? > > because nobody understands why it actually helped. While working with a customer we found this patch and it did solve the original reporters' problem and matched the issue reported by Vladimir. > > and please note that this patch is buggy, fixed by dfd01f0260 > "sched/wait: Fix the signal handling fix" Ah, thanks, I missed that one! Since Peter's fix is on top of this change, how should we proceed with the stable-4.1 kernel? Alex, do you still actively maintain linux-4.1.y? > > Oleg. > > On 04/12, Florian Fainelli wrote: >> >> From: Peter Zijlstra >> >> [ Upstream commit 68985633bccb6066bf1803e316fbc6c1f5b796d6 ] >> >> Vladimir reported getting RCU stall warnings and bisected it back to >> commit: >> >> 743162013d40 ("sched: Remove proliferation of wait_on_bit() action functions") >> >> That commit inadvertently reversed the calls to schedule() and signal_pending(), >> thereby not handling the case where the signal receives while we sleep. >> >> Reported-by: Vladimir Murzin >> Tested-by: Vladimir Murzin >> Signed-off-by: Peter Zijlstra (Intel) >> Cc: Linus Torvalds >> Cc: Mike Galbraith >> Cc: Peter Zijlstra >> Cc: Thomas Gleixner >> Cc: mark.rutland@arm.com >> Cc: neilb@suse.de >> Cc: oleg@redhat.com >> Fixes: 743162013d40 ("sched: Remove proliferation of wait_on_bit() action functions") >> Fixes: cbbce8220949 ("SCHED: add some "wait..on_bit...timeout()" interfaces.") >> Link: http://lkml.kernel.org/r/20151201130404.GL3816@twins.programming.kicks-ass.net >> Signed-off-by: Ingo Molnar >> --- >> kernel/sched/wait.c | 16 ++++++++-------- >> 1 file changed, 8 insertions(+), 8 deletions(-) >> >> diff --git a/kernel/sched/wait.c b/kernel/sched/wait.c >> index 852143a79f36..e0bb7e6c4fb0 100644 >> --- a/kernel/sched/wait.c >> +++ b/kernel/sched/wait.c >> @@ -583,18 +583,18 @@ EXPORT_SYMBOL(wake_up_atomic_t); >> >> __sched int bit_wait(struct wait_bit_key *word) >> { >> - if (signal_pending_state(current->state, current)) >> - return 1; >> schedule(); >> + if (signal_pending(current)) >> + return -EINTR; >> return 0; >> } >> EXPORT_SYMBOL(bit_wait); >> >> __sched int bit_wait_io(struct wait_bit_key *word) >> { >> - if (signal_pending_state(current->state, current)) >> - return 1; >> io_schedule(); >> + if (signal_pending(current)) >> + return -EINTR; >> return 0; >> } >> EXPORT_SYMBOL(bit_wait_io); >> @@ -602,11 +602,11 @@ EXPORT_SYMBOL(bit_wait_io); >> __sched int bit_wait_timeout(struct wait_bit_key *word) >> { >> unsigned long now = ACCESS_ONCE(jiffies); >> - if (signal_pending_state(current->state, current)) >> - return 1; >> if (time_after_eq(now, word->timeout)) >> return -EAGAIN; >> schedule_timeout(word->timeout - now); >> + if (signal_pending(current)) >> + return -EINTR; >> return 0; >> } >> EXPORT_SYMBOL_GPL(bit_wait_timeout); >> @@ -614,11 +614,11 @@ EXPORT_SYMBOL_GPL(bit_wait_timeout); >> __sched int bit_wait_io_timeout(struct wait_bit_key *word) >> { >> unsigned long now = ACCESS_ONCE(jiffies); >> - if (signal_pending_state(current->state, current)) >> - return 1; >> if (time_after_eq(now, word->timeout)) >> return -EAGAIN; >> io_schedule_timeout(word->timeout - now); >> + if (signal_pending(current)) >> + return -EINTR; >> return 0; >> } >> EXPORT_SYMBOL_GPL(bit_wait_io_timeout); >> -- >> 2.12.1 >> > -- Florian