From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754812AbaILNgH (ORCPT ); Fri, 12 Sep 2014 09:36:07 -0400 Received: from shelob.surriel.com ([74.92.59.67]:59603 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754734AbaILNgE (ORCPT ); Fri, 12 Sep 2014 09:36:04 -0400 From: riel@redhat.com To: peterz@infradead.org Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, prarit@redhat.com, oleg@redhat.com, sgruszka@redhat.com Subject: [PATCH -tip 2/2] sched,time: fix lock inversion in thread_group_cputime Date: Fri, 12 Sep 2014 09:12:15 -0400 Message-Id: <1410527535-9814-3-git-send-email-riel@redhat.com> X-Mailer: git-send-email 1.9.3 In-Reply-To: <1410527535-9814-1-git-send-email-riel@redhat.com> References: <1410527535-9814-1-git-send-email-riel@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Rik van Riel The sig->stats_lock nests inside the tasklist_lock and the sighand->siglock in __exit_signal and wait_task_zombie. However, both of those locks can be taken from irq context, which means we need to use the interrupt safe variant of read_seqbegin_or_lock. This blocks interrupts when the "lock" branch is taken (seq is odd), preventing the lock inversion. On the first (lockless) pass through the loop, irqs are not blocked. Signed-off-by: Rik van Riel Reported-by: Stanislaw Gruszka --- kernel/sched/cputime.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c index 2b57031..64492df 100644 --- a/kernel/sched/cputime.c +++ b/kernel/sched/cputime.c @@ -289,13 +289,14 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times) cputime_t utime, stime; struct task_struct *t; unsigned int seq, nextseq; + unsigned long flags; rcu_read_lock(); /* Attempt a lockless read on the first round. */ nextseq = 0; do { seq = nextseq; - read_seqbegin_or_lock(&sig->stats_lock, &seq); + flags = read_seqbegin_or_lock_irqsave(&sig->stats_lock, &seq); times->utime = sig->utime; times->stime = sig->stime; times->sum_exec_runtime = sig->sum_sched_runtime; @@ -309,7 +310,7 @@ void thread_group_cputime(struct task_struct *tsk, struct task_cputime *times) /* If lockless access failed, take the lock. */ nextseq = 1; } while (need_seqretry(&sig->stats_lock, seq)); - done_seqretry(&sig->stats_lock, seq); + done_seqretry_irqrestore(&sig->stats_lock, seq, flags); rcu_read_unlock(); } -- 1.9.3