Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935029Ab3JPSRB (ORCPT ); Wed, 16 Oct 2013 14:17:01 -0400 Received: from mail-ve0-f201.google.com ([209.85.128.201]:52222 "EHLO mail-ve0-f201.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934978Ab3JPSQP (ORCPT ); Wed, 16 Oct 2013 14:16:15 -0400 Subject: [PATCH 1/5] sched: Fix race on toggling cfs_bandwidth_used To: peterz@infradead.org, mingo@redhat.com From: Ben Segall Cc: pjt@google.com, linux-kernel@vger.kernel.org Date: Wed, 16 Oct 2013 11:16:12 -0700 Message-ID: <20131016181611.22647.80365.stgit@sword-of-the-dawn.mtv.corp.google.com> In-Reply-To: <20131016181548.22647.17161.stgit@sword-of-the-dawn.mtv.corp.google.com> References: <20131016181548.22647.17161.stgit@sword-of-the-dawn.mtv.corp.google.com> User-Agent: StGit/0.16 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3614 Lines: 101 When we transition cfs_bandwidth_used to false, any currently throttled groups will incorrectly return false from cfs_rq_throttled. While tg_set_cfs_bandwidth will unthrottle them eventually, currently running code (including at least dequeue_task_fair and distribute_cfs_runtime) will cause errors. Fix this by turning off cfs_bandwidth_used only after unthrottling all cfs_rqs. Tested: toggle bandwidth back and forth on a loaded cgroup. Caused crashes in minutes without the patch, hasn't crashed with it. Signed-off-by: Ben Segall --- kernel/sched/core.c | 9 ++++++++- kernel/sched/fair.c | 16 +++++++++------- kernel/sched/sched.h | 3 ++- 3 files changed, 19 insertions(+), 9 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 0c3feeb..2d2ac236 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7433,7 +7433,12 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) runtime_enabled = quota != RUNTIME_INF; runtime_was_enabled = cfs_b->quota != RUNTIME_INF; - account_cfs_bandwidth_used(runtime_enabled, runtime_was_enabled); + /* + * If we need to toggle cfs_bandwidth_used, off->on must occur + * before making related changes, and on->off must occur afterwards + */ + if (runtime_enabled && !runtime_was_enabled) + cfs_bandwidth_usage_inc(); raw_spin_lock_irq(&cfs_b->lock); cfs_b->period = ns_to_ktime(period); cfs_b->quota = quota; @@ -7459,6 +7464,8 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota) unthrottle_cfs_rq(cfs_rq); raw_spin_unlock_irq(&rq->lock); } + if (runtime_was_enabled && !runtime_enabled) + cfs_bandwidth_usage_dec(); out_unlock: mutex_unlock(&cfs_constraints_mutex); diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 4aa0b10..67c9ecf 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2854,13 +2854,14 @@ static inline bool cfs_bandwidth_used(void) return static_key_false(&__cfs_bandwidth_used); } -void account_cfs_bandwidth_used(int enabled, int was_enabled) +void cfs_bandwidth_usage_inc(void) { - /* only need to count groups transitioning between enabled/!enabled */ - if (enabled && !was_enabled) - static_key_slow_inc(&__cfs_bandwidth_used); - else if (!enabled && was_enabled) - static_key_slow_dec(&__cfs_bandwidth_used); + static_key_slow_inc(&__cfs_bandwidth_used); +} + +void cfs_bandwidth_usage_dec(void) +{ + static_key_slow_dec(&__cfs_bandwidth_used); } #else /* HAVE_JUMP_LABEL */ static bool cfs_bandwidth_used(void) @@ -2868,7 +2869,8 @@ static bool cfs_bandwidth_used(void) return true; } -void account_cfs_bandwidth_used(int enabled, int was_enabled) {} +void cfs_bandwidth_usage_inc(void) {} +void cfs_bandwidth_usage_dec(void) {} #endif /* HAVE_JUMP_LABEL */ /* diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index d69cb32..d73761f 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1334,7 +1334,8 @@ extern void print_rt_stats(struct seq_file *m, int cpu); extern void init_cfs_rq(struct cfs_rq *cfs_rq); extern void init_rt_rq(struct rt_rq *rt_rq, struct rq *rq); -extern void account_cfs_bandwidth_used(int enabled, int was_enabled); +extern void cfs_bandwidth_usage_inc(void); +extern void cfs_bandwidth_usage_dec(void); #ifdef CONFIG_NO_HZ_COMMON enum rq_nohz_flag_bits { -- 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/