From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ben Segall , Peter Zijlstra , pjt@google.com, Ingo Molnar , Chris J Arges Subject: [PATCH 3.4 39/43] sched: Avoid throttle_cfs_rq() racing with period_timer stopping Date: Mon, 6 Jan 2014 14:39:56 -0800 Message-Id: <20140106223943.364444378@linuxfoundation.org> In-Reply-To: <20140106223942.259651490@linuxfoundation.org> References: <20140106223942.259651490@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: 3.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Ben Segall commit f9f9ffc237dd924f048204e8799da74f9ecf40cf upstream. throttle_cfs_rq() doesn't check to make sure that period_timer is running, and while update_curr/assign_cfs_runtime does, a concurrently running period_timer on another cpu could cancel itself between this cpu's update_curr and throttle_cfs_rq(). If there are no other cfs_rqs running in the tg to restart the timer, this causes the cfs_rq to be stranded forever. Fix this by calling __start_cfs_bandwidth() in throttle if the timer is inactive. (Also add some sched_debug lines for cfs_bandwidth.) Tested: make a run/sleep task in a cgroup, loop switching the cgroup between 1ms/100ms quota and unlimited, checking for timer_active=0 and throttled=1 as a failure. With the throttle_cfs_rq() change commented out this fails, with the full patch it passes. Signed-off-by: Ben Segall Signed-off-by: Peter Zijlstra Cc: pjt@google.com Link: http://lkml.kernel.org/r/20131016181632.22647.84174.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar Signed-off-by: Chris J Arges Signed-off-by: Greg Kroah-Hartman --- kernel/sched/debug.c | 8 ++++++++ kernel/sched/fair.c | 2 ++ 2 files changed, 10 insertions(+) --- a/kernel/sched/debug.c +++ b/kernel/sched/debug.c @@ -215,6 +215,14 @@ void print_cfs_rq(struct seq_file *m, in SEQ_printf(m, " .%-30s: %d\n", "load_tg", atomic_read(&cfs_rq->tg->load_weight)); #endif +#ifdef CONFIG_CFS_BANDWIDTH + SEQ_printf(m, " .%-30s: %d\n", "tg->cfs_bandwidth.timer_active", + cfs_rq->tg->cfs_bandwidth.timer_active); + SEQ_printf(m, " .%-30s: %d\n", "throttled", + cfs_rq->throttled); + SEQ_printf(m, " .%-30s: %d\n", "throttle_count", + cfs_rq->throttle_count); +#endif print_cfs_group_stats(m, cpu, cfs_rq->tg); #endif --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -1655,6 +1655,8 @@ static void throttle_cfs_rq(struct cfs_r cfs_rq->throttled_timestamp = rq->clock; raw_spin_lock(&cfs_b->lock); list_add_tail_rcu(&cfs_rq->throttled_list, &cfs_b->throttled_cfs_rq); + if (!cfs_b->timer_active) + __start_cfs_bandwidth(cfs_b); raw_spin_unlock(&cfs_b->lock); }