From: Ben Segall Date: Wed, 16 Oct 2013 18:16:32 +0000 (-0700) Subject: sched: Avoid throttle_cfs_rq() racing with period_timer stopping X-Git-Tag: v3.2.54~39 X-Git-Url: https://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=49c5317fa0fa5d0dfa5d15dc3010e2578beddb16;p=pandora-kernel.git sched: Avoid throttle_cfs_rq() racing with period_timer stopping 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 [bwh: Backported to 3.2: adjust filenames] Signed-off-by: Ben Hutchings --- diff --git a/kernel/sched_debug.c b/kernel/sched_debug.c index a6710a112b4f..f4010e2820fc 100644 --- a/kernel/sched_debug.c +++ b/kernel/sched_debug.c @@ -213,6 +213,14 @@ void print_cfs_rq(struct seq_file *m, int cpu, struct cfs_rq *cfs_rq) 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 diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index c261da7ddc71..5b9e456ea98c 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1527,6 +1527,8 @@ static void throttle_cfs_rq(struct cfs_rq *cfs_rq) 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); }