Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760583Ab3GZXn3 (ORCPT ); Fri, 26 Jul 2013 19:43:29 -0400 Received: from mail-we0-f177.google.com ([74.125.82.177]:38178 "EHLO mail-we0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760368Ab3GZXnS (ORCPT ); Fri, 26 Jul 2013 19:43:18 -0400 From: Frederic Weisbecker To: LKML Cc: Frederic Weisbecker , Steven Rostedt , "Paul E. McKenney" , Ingo Molnar , Thomas Gleixner , Peter Zijlstra , Borislav Petkov , Li Zhong , Mike Galbraith , Kevin Hilman Subject: [PATCH 13/21] vtime: Fix racy cputime delta update Date: Sat, 27 Jul 2013 01:42:36 +0200 Message-Id: <1374882164-32519-14-git-send-email-fweisbec@gmail.com> X-Mailer: git-send-email 1.7.5.4 In-Reply-To: <1374882164-32519-1-git-send-email-fweisbec@gmail.com> References: <1374882164-32519-1-git-send-email-fweisbec@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1696 Lines: 48 get_vtime_delta() must be called under the task vtime_seqlock with the code that does the cputime accounting flush. Otherwise the cputime reader can be fooled and run into a race where it sees the snapshot update but misses the cputime flush. As a result it can report a cputime that is way too short. Fix vtime_account_user() that wasn't complying to that rule. Signed-off-by: Frederic Weisbecker Cc: Steven Rostedt Cc: Paul E. McKenney Cc: Ingo Molnar Cc: Thomas Gleixner Cc: Peter Zijlstra Cc: Borislav Petkov Cc: Li Zhong Cc: Mike Galbraith Cc: Kevin Hilman --- kernel/sched/cputime.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 5f273b47..b62d5c0 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -683,9 +683,10 @@ void vtime_account_irq_exit(struct task_struct *tsk) void vtime_account_user(struct task_struct *tsk) { - cputime_t delta_cpu = get_vtime_delta(tsk); + cputime_t delta_cpu; write_seqlock(&tsk->vtime_seqlock); + delta_cpu = get_vtime_delta(tsk); tsk->vtime_snap_whence = VTIME_SYS; account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu)); write_sequnlock(&tsk->vtime_seqlock); -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/