Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964852Ab3JPSQe (ORCPT ); Wed, 16 Oct 2013 14:16:34 -0400 Received: from mail-ob0-f202.google.com ([209.85.214.202]:40330 "EHLO mail-ob0-f202.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934666Ab3JPSQ2 (ORCPT ); Wed, 16 Oct 2013 14:16:28 -0400 Subject: [PATCH 4/5] sched: Guarantee new group-entities always have weight To: peterz@infradead.org, mingo@redhat.com From: Ben Segall Cc: pjt@google.com, linux-kernel@vger.kernel.org Date: Wed, 16 Oct 2013 11:16:27 -0700 Message-ID: <20131016181627.22647.47543.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: 1903 Lines: 56 From: Paul Turner 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 --- 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 fc44cc3..424c294 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7207,7 +7207,8 @@ 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/