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=-6.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 6F4A4C433E4 for ; Fri, 24 Jul 2020 10:41:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4A8002074B for ; Fri, 24 Jul 2020 10:41:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="N7W1YeX7" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726739AbgGXKlr (ORCPT ); Fri, 24 Jul 2020 06:41:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39660 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725889AbgGXKlq (ORCPT ); Fri, 24 Jul 2020 06:41:46 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 993A3C0619D3 for ; Fri, 24 Jul 2020 03:41:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=FldjSuaYgsda6J4qQh4t1AAP693GlnRUaBrzzoUB0Ss=; b=N7W1YeX7gw/k9lv0xeD9WdryTk ETaMxtK88rkYpPoCLB23XfBwovS0UBElddMuj/FOepst9fii/Ea+u7Jo/AF2GZ0viF35KkHJOXZZ3 GFp6rCZSbq1n7n4FtYC6JD0KGhVqquYFTPM3cA8uhoFOYJHZIMcpxTir150UdRhmKDRVQ4U8KlzyF ZgNfRv4bnOgLu6/QrRkE6cTabPskx/x64PP6tT1t7o/H3WAYR+u9pvg8FopFB2YEIjOP+VUZhsirQ JsHZlwP73q/awaz8S2Osijh0OeD9nG/gOuRmqkqll/0qSkR1z21S91We+30llBEpl+6iIsYPeY8qz U4FE2DVw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1jyv8m-0007tR-S2; Fri, 24 Jul 2020 10:41:25 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 059973003E5; Fri, 24 Jul 2020 12:41:20 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id E58832B7C0261; Fri, 24 Jul 2020 12:41:20 +0200 (CEST) Date: Fri, 24 Jul 2020 12:41:20 +0200 From: Peter Zijlstra To: Qais Yousef Cc: Ingo Molnar , Doug Anderson , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Patrick Bellasi , Chris Redpath , Lukasz Luba , linux-kernel@vger.kernel.org Subject: Re: [PATCH v7 3/3] sched/uclamp: Fix a deadlock when enabling uclamp static key Message-ID: <20200724104120.GY10769@hirez.programming.kicks-ass.net> References: <20200716110347.19553-1-qais.yousef@arm.com> <20200716110347.19553-4-qais.yousef@arm.com> <20200724091244.GX10769@hirez.programming.kicks-ass.net> <20200724094650.hgya5j7i7lbhrocy@e107158-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200724094650.hgya5j7i7lbhrocy@e107158-lin.cambridge.arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jul 24, 2020 at 10:46:50AM +0100, Qais Yousef wrote: > On 07/24/20 11:12, Peter Zijlstra wrote: > > On Thu, Jul 16, 2020 at 12:03:47PM +0100, Qais Yousef wrote: > > > > I've trimmed the Changelog to read like: > > +1 > > Should we mention the ordering issue too? Or maybe I misinterpreted the > 'Possible unsafe locking scenario' part? The lock inversion was, imo, secondary. It only existed because of the impossible lock ordering -- taking a blocking lock inside an atomic lock. Fixing the first, avoids the second etc.. So I left it out. > This should work, but you'll need to sprinkle ifdef around the key. Or move it > to uclamp_validate() Indeed, the patch now reads like: --- Subject: sched/uclamp: Fix a deadlock when enabling uclamp static key From: Qais Yousef Date: Thu, 16 Jul 2020 12:03:47 +0100 From: Qais Yousef 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 --- kernel/sched/core.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -1252,6 +1252,15 @@ static int uclamp_validate(struct task_s 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; } @@ -1282,8 +1291,6 @@ static void __setscheduler_uclamp(struct 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);