From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71378C433E2 for ; Fri, 28 Aug 2020 12:56:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5289920872 for ; Fri, 28 Aug 2020 12:56:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729496AbgH1M44 (ORCPT ); Fri, 28 Aug 2020 08:56:56 -0400 Received: from foss.arm.com ([217.140.110.172]:48520 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729471AbgH1M4e (ORCPT ); Fri, 28 Aug 2020 08:56:34 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A4186D6E; Fri, 28 Aug 2020 05:56:33 -0700 (PDT) Received: from e107158-lin.cambridge.arm.com (e107158-lin.cambridge.arm.com [10.1.195.21]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 89E183F66B; Fri, 28 Aug 2020 05:56:32 -0700 (PDT) From: Qais Yousef To: Greg Kroah-Hartman , Sasha Levin Cc: stable@vger.kernel.org, linux-kernel@vger.kernel.org, "Peter Zijlstra (Intel)" , Mel Gorman , Dietmar Eggemann , Qais Yousef Subject: [PATCH 2/2] sched/uclamp: Fix a deadlock when enabling uclamp static key Date: Fri, 28 Aug 2020 13:56:10 +0100 Message-Id: <20200828125610.30943-3-qais.yousef@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20200828125610.30943-1-qais.yousef@arm.com> References: <20200828125610.30943-1-qais.yousef@arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following splat was caught when setting uclamp value of a task: BUG: sleeping function called from invalid context at ./include/linux/percpu-rwsem.h:49 cpus_read_lock+0x68/0x130 static_key_enable+0x1c/0x38 __sched_setscheduler+0x900/0xad8 Fix by ensuring we enable the key outside of the critical section in __sched_setscheduler() Fixes: 46609ce22703 ("sched/uclamp: Protect uclamp fast path code with static key") Signed-off-by: Qais Yousef Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20200716110347.19553-4-qais.yousef@arm.com (cherry picked from commit e65855a52b479f98674998cb23b21ef5a8144b04) Signed-off-by: Qais Yousef --- kernel/sched/core.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index a8ab68aa189a..352239c411a4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1249,6 +1249,15 @@ static int uclamp_validate(struct task_struct *p, if (upper_bound > SCHED_CAPACITY_SCALE) return -EINVAL; + /* + * We have valid uclamp attributes; make sure uclamp is enabled. + * + * We need to do that here, because enabling static branches is a + * blocking operation which obviously cannot be done while holding + * scheduler locks. + */ + static_branch_enable(&sched_uclamp_used); + return 0; } @@ -1279,8 +1288,6 @@ static void __setscheduler_uclamp(struct task_struct *p, if (likely(!(attr->sched_flags & SCHED_FLAG_UTIL_CLAMP))) return; - static_branch_enable(&sched_uclamp_used); - if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP_MIN) { uclamp_se_set(&p->uclamp_req[UCLAMP_MIN], attr->sched_util_min, true); -- 2.17.1