From patchwork Tue Dec 17 19:27:37 2013 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: John Stultz X-Patchwork-Id: 22610 Return-Path: X-Original-To: linaro@patches.linaro.org Delivered-To: linaro@patches.linaro.org Received: from mail-ob0-f198.google.com (mail-ob0-f198.google.com [209.85.214.198]) by ip-10-151-82-157.ec2.internal (Postfix) with ESMTPS id 81EED23FC6 for ; Tue, 17 Dec 2013 19:27:52 +0000 (UTC) Received: by mail-ob0-f198.google.com with SMTP id wo20sf23447774obc.5 for ; Tue, 17 Dec 2013 11:27:51 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:delivered-to:from:to:cc:subject :date:message-id:in-reply-to:references:x-original-sender :x-original-authentication-results:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-unsubscribe; bh=t3yMQ9eawrAs4nQl1UvbVdnfdP3ece3d5eHdonKX9HY=; b=YDVmVlU88e9wxXhFbYI4IPIwZyRnWXf+ZZCaYQlh4OoeUbcMDPsbJWapy1oVTLpmSD 2TveWjXm/xWIM2Lno8QWqDTLKgI4nGxecXaQXaVRgx0KgQ++/EoRLg8scgVsyepRAhiL TbsvVmw6nT78qaHH9RqqgpdbichnXHFt6DFSlHVdGmkq0Rq9tTPmvv8xcUcqGxuRpCfy TQ3gMUpZKE4fZVG95CAwp8JxwliN08hd1gFFYybftSy5h7rDVGSYddSY4al+WWw6fo54 RKpbaMvxZ69khP1hkJCUjqPbljC1fTqRtTVkSkZv4FGfS/gZoYGl8vqQjQQVgkyoM9af mWvw== X-Gm-Message-State: ALoCoQk211gYw2ttoS9rwdpEe1K4qs4SuZnEzXqp9pNOTjHWtKrTyQJO/1WWiylcyKC1BLL2YOio X-Received: by 10.43.128.197 with SMTP id hf5mr7676585icc.2.1387308471677; Tue, 17 Dec 2013 11:27:51 -0800 (PST) MIME-Version: 1.0 X-BeenThere: patchwork-forward@linaro.org Received: by 10.49.35.108 with SMTP id g12ls2584406qej.81.gmail; Tue, 17 Dec 2013 11:27:51 -0800 (PST) X-Received: by 10.52.0.142 with SMTP id 14mr72259vde.94.1387308471551; Tue, 17 Dec 2013 11:27:51 -0800 (PST) Received: from mail-vc0-f175.google.com (mail-vc0-f175.google.com [209.85.220.175]) by mx.google.com with ESMTPS id gq10si5121903vdc.82.2013.12.17.11.27.51 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 17 Dec 2013 11:27:51 -0800 (PST) Received-SPF: neutral (google.com: 209.85.220.175 is neither permitted nor denied by best guess record for domain of patch+caf_=patchwork-forward=linaro.org@linaro.org) client-ip=209.85.220.175; Received: by mail-vc0-f175.google.com with SMTP id ld13so4375689vcb.6 for ; Tue, 17 Dec 2013 11:27:51 -0800 (PST) X-Received: by 10.58.39.97 with SMTP id o1mr11255875vek.15.1387308471435; Tue, 17 Dec 2013 11:27:51 -0800 (PST) X-Forwarded-To: patchwork-forward@linaro.org X-Forwarded-For: patch@linaro.org patchwork-forward@linaro.org Delivered-To: patches@linaro.org Received: by 10.59.13.131 with SMTP id ey3csp190158ved; Tue, 17 Dec 2013 11:27:50 -0800 (PST) X-Received: by 10.68.244.2 with SMTP id xc2mr1865328pbc.58.1387308470169; Tue, 17 Dec 2013 11:27:50 -0800 (PST) Received: from mail-pd0-f180.google.com (mail-pd0-f180.google.com [209.85.192.180]) by mx.google.com with ESMTPS id ez5si12407349pab.309.2013.12.17.11.27.49 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 17 Dec 2013 11:27:50 -0800 (PST) Received-SPF: neutral (google.com: 209.85.192.180 is neither permitted nor denied by best guess record for domain of john.stultz@linaro.org) client-ip=209.85.192.180; Received: by mail-pd0-f180.google.com with SMTP id q10so7169221pdj.25 for ; Tue, 17 Dec 2013 11:27:49 -0800 (PST) X-Received: by 10.68.235.72 with SMTP id uk8mr29091045pbc.93.1387308469641; Tue, 17 Dec 2013 11:27:49 -0800 (PST) Received: from localhost.localdomain (c-67-170-153-23.hsd1.or.comcast.net. [67.170.153.23]) by mx.google.com with ESMTPSA id yg3sm48436118pab.16.2013.12.17.11.27.47 for (version=TLSv1.1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 17 Dec 2013 11:27:48 -0800 (PST) From: John Stultz To: LKML Cc: John Stultz , Thomas Gleixner , Prarit Bhargava , Richard Cochran , Ingo Molnar , Sasha Levin , stable Subject: [PATCH 3/3] timekeeping: Avoid possible deadlock from clock_was_set_delayed Date: Tue, 17 Dec 2013 11:27:37 -0800 Message-Id: <1387308457-25364-4-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.8.3.2 In-Reply-To: <1387308457-25364-1-git-send-email-john.stultz@linaro.org> References: <1387308457-25364-1-git-send-email-john.stultz@linaro.org> X-Removed-Original-Auth: Dkim didn't pass. X-Original-Sender: john.stultz@linaro.org X-Original-Authentication-Results: mx.google.com; spf=neutral (google.com: 209.85.220.175 is neither permitted nor denied by best guess record for domain of patch+caf_=patchwork-forward=linaro.org@linaro.org) smtp.mail=patch+caf_=patchwork-forward=linaro.org@linaro.org Precedence: list Mailing-list: list patchwork-forward@linaro.org; contact patchwork-forward+owners@linaro.org List-ID: X-Google-Group-Id: 836684582541 List-Post: , List-Help: , List-Archive: List-Unsubscribe: , As part of normal operaions, the hrtimer subsystem frequently calls into the timekeeping code, creating a locking order of hrtimer locks -> timekeeping locks clock_was_set_delayed() was suppoed to allow us to avoid deadlocks between the timekeeping the hrtimer subsystem, so that we could notify the hrtimer subsytem the time had changed while holding the timekeeping locks. This was done by scheduling delayed work that would run later once we were out of the timekeeing code. But unfortunately the lock chains are complex enoguh that in scheduling delayed work, we end up eventually trying to grab an hrtimer lock. Sasha Levin noticed this in testing when the new seqlock lockdep enablement triggered the following (somewhat abrieviated) message: [ 251.100221] ====================================================== [ 251.100221] [ INFO: possible circular locking dependency detected ] [ 251.100221] 3.13.0-rc2-next-20131206-sasha-00005-g8be2375-dirty #4053 Not tainted [ 251.101967] ------------------------------------------------------- [ 251.101967] kworker/10:1/4506 is trying to acquire lock: [ 251.101967] (timekeeper_seq){----..}, at: [] retrigger_next_event+0x56/0x70 [ 251.101967] [ 251.101967] but task is already holding lock: [ 251.101967] (hrtimer_bases.lock#11){-.-...}, at: [] retrigger_next_event+0x3c/0x70 [ 251.101967] [ 251.101967] which lock already depends on the new lock. [ 251.101967] [ 251.101967] [ 251.101967] the existing dependency chain (in reverse order) is: [ 251.101967] -> #5 (hrtimer_bases.lock#11){-.-...}: [snipped] -> #4 (&rt_b->rt_runtime_lock){-.-...}: [snipped] -> #3 (&rq->lock){-.-.-.}: [snipped] -> #2 (&p->pi_lock){-.-.-.}: [snipped] -> #1 (&(&pool->lock)->rlock){-.-...}: [ 251.101967] [] validate_chain+0x6c3/0x7b0 [ 251.101967] [] __lock_acquire+0x4ad/0x580 [ 251.101967] [] lock_acquire+0x182/0x1d0 [ 251.101967] [] _raw_spin_lock+0x40/0x80 [ 251.101967] [] __queue_work+0x1a9/0x3f0 [ 251.101967] [] queue_work_on+0x98/0x120 [ 251.101967] [] clock_was_set_delayed+0x21/0x30 [ 251.101967] [] do_adjtimex+0x111/0x160 [ 251.101967] [] compat_sys_adjtimex+0x41/0x70 [ 251.101967] [] ia32_sysret+0x0/0x5 [ 251.101967] -> #0 (timekeeper_seq){----..}: [snipped] [ 251.101967] other info that might help us debug this: [ 251.101967] [ 251.101967] Chain exists of: timekeeper_seq --> &rt_b->rt_runtime_lock --> hrtimer_bases.lock#11 [ 251.101967] Possible unsafe locking scenario: [ 251.101967] [ 251.101967] CPU0 CPU1 [ 251.101967] ---- ---- [ 251.101967] lock(hrtimer_bases.lock#11); [ 251.101967] lock(&rt_b->rt_runtime_lock); [ 251.101967] lock(hrtimer_bases.lock#11); [ 251.101967] lock(timekeeper_seq); [ 251.101967] [ 251.101967] *** DEADLOCK *** [ 251.101967] [ 251.101967] 3 locks held by kworker/10:1/4506: [ 251.101967] #0: (events){.+.+.+}, at: [] process_one_work+0x200/0x530 [ 251.101967] #1: (hrtimer_work){+.+...}, at: [] process_one_work+0x200/0x530 [ 251.101967] #2: (hrtimer_bases.lock#11){-.-...}, at: [] retrigger_next_event+0x3c/0x70 [ 251.101967] [ 251.101967] stack backtrace: [ 251.101967] CPU: 10 PID: 4506 Comm: kworker/10:1 Not tainted 3.13.0-rc2-next-20131206-sasha-00005-g8be2375-dirty #4053 [ 251.101967] Workqueue: events clock_was_set_work So the best solution is to avoid calling clock_was_set_delayed() while holding the timekeeping lock, and instead using a flag variable to decide if we should call clock_was_set() once we've released the locks. This works for the case here, where the do_adjtimex() was the deadlock trigger point. Unfortuantely, in update_wall_time() we still hold the jiffies lock, which would deadlock with the ipi triggered by clock_was_set(), preventing us from calling it even after we drop the timekeeping lock. So instead call clock_was_set_delayed() at that point. Cc: Thomas Gleixner Cc: Prarit Bhargava Cc: Richard Cochran Cc: Ingo Molnar Cc: Sasha Levin Cc: stable #3.10+ Reported-by: Sasha Levin Tested-by: Sasha Levin Signed-off-by: John Stultz --- kernel/time/timekeeping.c | 18 ++++++++++++++++-- 1 file changed, 16 insertions(+), 2 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 998ec751..c1d36b6 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1278,7 +1278,6 @@ static inline unsigned int accumulate_nsecs_to_secs(struct timekeeper *tk) __timekeeping_set_tai_offset(tk, tk->tai_offset - leap); - clock_was_set_delayed(); action = TK_CLOCK_WAS_SET; } } @@ -1440,6 +1439,19 @@ static void update_wall_time(void) write_seqcount_end(&timekeeper_seq); out: raw_spin_unlock_irqrestore(&timekeeper_lock, flags); + if (action & TK_CLOCK_WAS_SET) { + /* + * XXX - I'd rather we just call clock_was_set(), but + * since we're currently holding the jiffies lock, calling + * clock_was_set would trigger an ipi which would then grab + * the jiffies lock and we'd deadlock. :( + * The right solution should probably be droping + * the jiffies lock before calling update_wall_time + * but that requires some rework of the tick sched + * code. + */ + clock_was_set_delayed(); + } } /** @@ -1700,11 +1712,13 @@ int do_adjtimex(struct timex *txc) if (tai != orig_tai) { __timekeeping_set_tai_offset(tk, tai); timekeeping_update(tk, TK_MIRROR | TK_CLOCK_WAS_SET); - clock_was_set_delayed(); } write_seqcount_end(&timekeeper_seq); raw_spin_unlock_irqrestore(&timekeeper_lock, flags); + if (tai != orig_tai) + clock_was_set(); + ntp_notify_cmos_timer(); return ret;