From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-19.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ABC8CC4708F for ; Fri, 4 Jun 2021 11:32:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 86CF56141E for ; Fri, 4 Jun 2021 11:32:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230127AbhFDLdx (ORCPT ); Fri, 4 Jun 2021 07:33:53 -0400 Received: from mail.kernel.org ([198.145.29.99]:34258 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229740AbhFDLdw (ORCPT ); Fri, 4 Jun 2021 07:33:52 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 324B7613FE; Fri, 4 Jun 2021 11:32:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1622806326; bh=UWTB2JFFGx0hcRAEvHxRwyTX7+TIbdrCudgu0abih/g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=cq9TMtMHx0mYceKQb9ptwNprxG0ZFt5uFO26KIYexU9b5z4f0wu0f2viwiEMXjUiV 4iU4gogV+Y5kZE7beYbv60i3Aotp2VGzICptpE1FRRfU2M2CZj+LzjKcMLOddartIV 8jnz+1fHahJQVrxolHNdoui7E5232hYJz/ha+DsNkNUYrbti4Y4ST5OefKIRkoxLCl IRCjS27wL0uyFEU1P/Z+o6NrZ72Bsm1JZhmRmG3HIL/6aRYYatMB17J3ADUfpnbeR7 gWpclEjsw2x9lZx10gODV7iLxEwgfLreHP8Qtqi+cNB9BXNu0c5VFVGcluVdn2HEoF cVzqycb+py4mQ== From: Frederic Weisbecker To: Thomas Gleixner Cc: LKML , Frederic Weisbecker , Peter Zijlstra , "Eric W . Biederman" , Oleg Nesterov , Ingo Molnar Subject: [PATCH 1/6] posix-cpu-timers: Fix rearm racing against process tick Date: Fri, 4 Jun 2021 13:31:54 +0200 Message-Id: <20210604113159.26177-2-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210604113159.26177-1-frederic@kernel.org> References: <20210604113159.26177-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since the process wide cputime counter is started locklessly from posix_cpu_timer_rearm(), it can be concurrently stopped by operations on other timers from the same thread group, such as in the following unlucky scenario: CPU 0 CPU 1 ----- ----- timer_settime(TIMER B) posix_cpu_timer_rearm(TIMER A) cpu_clock_sample_group() (pct->timers_active already true) handle_posix_cpu_timers() check_process_timers() stop_process_timers() pct->timers_active = false arm_timer(TIMER A) tick -> run_posix_cpu_timers() // sees !pct->timers_active, ignore // our TIMER A Fix this with simply locking process wide cputime counting start and timer arm in the same block. Signed-off-by: Frederic Weisbecker Cc: Oleg Nesterov Cc: Thomas Gleixner Cc: Peter Zijlstra (Intel) Cc: Ingo Molnar Cc: Eric W. Biederman --- kernel/time/posix-cpu-timers.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/kernel/time/posix-cpu-timers.c b/kernel/time/posix-cpu-timers.c index 3bb96a8b49c9..aa52fc85dbcb 100644 --- a/kernel/time/posix-cpu-timers.c +++ b/kernel/time/posix-cpu-timers.c @@ -991,6 +991,11 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer) if (!p) goto out; + /* Protect timer list r/w in arm_timer() */ + sighand = lock_task_sighand(p, &flags); + if (unlikely(sighand == NULL)) + goto out; + /* * Fetch the current sample and update the timer's expiry time. */ @@ -1001,11 +1006,6 @@ static void posix_cpu_timer_rearm(struct k_itimer *timer) bump_cpu_timer(timer, now); - /* Protect timer list r/w in arm_timer() */ - sighand = lock_task_sighand(p, &flags); - if (unlikely(sighand == NULL)) - goto out; - /* * Now re-arm for the new expiry time. */ -- 2.25.1