From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932174AbbFQRGA (ORCPT ); Wed, 17 Jun 2015 13:06:00 -0400 Received: from mail-pa0-f43.google.com ([209.85.220.43]:36246 "EHLO mail-pa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754335AbbFQRF6 (ORCPT ); Wed, 17 Jun 2015 13:05:58 -0400 From: John Stultz To: lkml Cc: John Stultz , Prarit Bhargava , Daniel Bristot de Oliveira , Richard Cochran , Jan Kara , Jiri Bohac , Ingo Molnar , Thomas Gleixner Subject: [PATCH] timekeeping: Copy the shadow-timekeeper over the real timekeeper last Date: Wed, 17 Jun 2015 10:05:53 -0700 Message-Id: <1434560753-7441-1-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. Cc: Prarit Bhargava Cc: Daniel Bristot de Oliveira Cc: Richard Cochran Cc: Jan Kara Cc: Jiri Bohac Cc: Ingo Molnar Cc: Thomas Gleixner Reported-by: Prarit Bhargava Tested-by: Prarit Bhargava Tested-by: Daniel Bristot de Oliveira Signed-off-by: John Stultz --- (This patch applies to tip/timers/core) 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); -- 1.9.1