Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758122Ab3J2OK6 (ORCPT ); Tue, 29 Oct 2013 10:10:58 -0400 Received: from terminus.zytor.com ([198.137.202.10]:45885 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757033Ab3J2OIM (ORCPT ); Tue, 29 Oct 2013 10:08:12 -0400 Date: Tue, 29 Oct 2013 07:07:40 -0700 From: tip-bot for Paul Turner Message-ID: Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@kernel.org, peterz@infradead.org, pjt@google.com, tglx@linutronix.de Reply-To: mingo@kernel.org, hpa@zytor.com, linux-kernel@vger.kernel.org, pjt@google.com, peterz@infradead.org, tglx@linutronix.de In-Reply-To: <20131016181627.22647.47543.stgit@sword-of-the-dawn.mtv.corp.google.com> References: <20131016181627.22647.47543.stgit@sword-of-the-dawn.mtv.corp.google.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched: Guarantee new group-entities always have weight Git-Commit-ID: 0ac9b1c21874d2490331233b3242085f8151e166 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.1 (terminus.zytor.com [127.0.0.1]); Tue, 29 Oct 2013 07:07:46 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2449 Lines: 65 Commit-ID: 0ac9b1c21874d2490331233b3242085f8151e166 Gitweb: http://git.kernel.org/tip/0ac9b1c21874d2490331233b3242085f8151e166 Author: Paul Turner AuthorDate: Wed, 16 Oct 2013 11:16:27 -0700 Committer: Ingo Molnar CommitDate: Tue, 29 Oct 2013 12:02:23 +0100 sched: Guarantee new group-entities always have weight Currently, group entity load-weights are initialized to zero. This admits some races with respect to the first time they are re-weighted in earlty use. ( Let g[x] denote the se for "g" on cpu "x". ) Suppose that we have root->a and that a enters a throttled state, immediately followed by a[0]->t1 (the only task running on cpu[0]) blocking: put_prev_task(group_cfs_rq(a[0]), t1) put_prev_entity(..., t1) check_cfs_rq_runtime(group_cfs_rq(a[0])) throttle_cfs_rq(group_cfs_rq(a[0])) Then, before unthrottling occurs, let a[0]->b[0]->t2 wake for the first time: enqueue_task_fair(rq[0], t2) enqueue_entity(group_cfs_rq(b[0]), t2) enqueue_entity_load_avg(group_cfs_rq(b[0]), t2) account_entity_enqueue(group_cfs_ra(b[0]), t2) update_cfs_shares(group_cfs_rq(b[0])) < skipped because b is part of a throttled hierarchy > enqueue_entity(group_cfs_rq(a[0]), b[0]) ... We now have b[0] enqueued, yet group_cfs_rq(a[0])->load.weight == 0 which violates invariants in several code-paths. Eliminate the possibility of this by initializing group entity weight. Signed-off-by: Paul Turner Signed-off-by: Peter Zijlstra Link: http://lkml.kernel.org/r/20131016181627.22647.47543.stgit@sword-of-the-dawn.mtv.corp.google.com Signed-off-by: Ingo Molnar --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f6308cb..0923ab2 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7198,7 +7198,8 @@ void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq, se->cfs_rq = parent->my_q; se->my_q = cfs_rq; - update_load_set(&se->load, 0); + /* guarantee group entities always have weight */ + update_load_set(&se->load, NICE_0_LOAD); se->parent = parent; } -- 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/