From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752672AbbFRHb7 (ORCPT ); Thu, 18 Jun 2015 03:31:59 -0400 Received: from terminus.zytor.com ([198.137.202.10]:56669 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751867AbbFRHbv (ORCPT ); Thu, 18 Jun 2015 03:31:51 -0400 Date: Thu, 18 Jun 2015 00:31:33 -0700 From: tip-bot for John Stultz Message-ID: Cc: jack@suse.cz, jbohac@suse.cz, tglx@linutronix.de, bristot@redhat.com, mingo@kernel.org, richardcochran@gmail.com, john.stultz@linaro.org, hpa@zytor.com, linux-kernel@vger.kernel.org, prarit@redhat.com Reply-To: prarit@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, richardcochran@gmail.com, john.stultz@linaro.org, mingo@kernel.org, bristot@redhat.com, tglx@linutronix.de, jbohac@suse.cz, jack@suse.cz In-Reply-To: <1434560753-7441-1-git-send-email-john.stultz@linaro.org> References: <1434560753-7441-1-git-send-email-john.stultz@linaro.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:timers/core] timekeeping: Copy the shadow-timekeeper over the real timekeeper last Git-Commit-ID: 906c55579a6360dd9ef5a3101bb2e3ae396dfb97 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 906c55579a6360dd9ef5a3101bb2e3ae396dfb97 Gitweb: http://git.kernel.org/tip/906c55579a6360dd9ef5a3101bb2e3ae396dfb97 Author: John Stultz AuthorDate: Wed, 17 Jun 2015 10:05:53 -0700 Committer: Thomas Gleixner CommitDate: Thu, 18 Jun 2015 09:27:02 +0200 timekeeping: Copy the shadow-timekeeper over the real timekeeper last The fix in d151832650ed9 (time: Move clock_was_set_seq update before updating shadow-timekeeper) was unfortunately incomplete. The main gist of that change was to do the shadow-copy update last, so that any state changes were properly duplicated, and we wouldn't accidentally have stale data in the shadow. Unfortunately in the main update_wall_time() logic, we update use the shadow-timekeeper to calculate the next update values, then while holding the lock, copy the shadow-timekeeper over, then call timekeeping_update() to do some additional bookkeeping, (skipping the shadow mirror). The bug with this is the additional bookkeeping isn't all read-only, and some changes timkeeper state. Thus we might then overwrite this state change on the next update. To avoid this problem, do the timekeeping_update() on the shadow-timekeeper prior to copying the full state over to the real-timekeeper. This avoids problems with both the clock_was_set_seq and next_leap_ktime being overwritten and possibly the fast-timekeepers as well. Many thanks to Prarit for his rigorous testing, which discovered this problem, along with Prarit and Daniel's work validating this fix. Reported-by: Prarit Bhargava Tested-by: Prarit Bhargava Tested-by: Daniel Bristot de Oliveira Signed-off-by: John Stultz Cc: Richard Cochran Cc: Jan Kara Cc: Jiri Bohac Cc: Ingo Molnar Link: http://lkml.kernel.org/r/1434560753-7441-1-git-send-email-john.stultz@linaro.org Signed-off-by: Thomas Gleixner --- kernel/time/timekeeping.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 5d67ffb..30b7a40 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1853,8 +1853,9 @@ void update_wall_time(void) * memcpy under the tk_core.seq against one before we start * updating. */ + timekeeping_update(tk, clock_set); memcpy(real_tk, tk, sizeof(*tk)); - timekeeping_update(real_tk, clock_set); + /* The memcpy must come last. Do not put anything here! */ write_seqcount_end(&tk_core.seq); out: raw_spin_unlock_irqrestore(&timekeeper_lock, flags);