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=-8.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 EEC0FC2D0E4 for ; Thu, 19 Nov 2020 11:29:17 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 696B72168B for ; Thu, 19 Nov 2020 11:29:17 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="aYPeOZLg" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 696B72168B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:MIME-Version:Message-ID:Date:In-reply-to:Subject:To: From:References:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=TkbVk+6vRELbmY5B7+fXp/lMtUx3+PqU/ljLh+xJDzI=; b=aYPeOZLgeU2nsFEixKciX2gEj E7Gqk8BRGOez12mMp7063fMjvGUxBClR9UIWPgZXf0+tMNL+XhPhT0kuqiN7ArXQ/ky2VleujA5Fu zr1bNFfFfFlt4Fr3DnmtKLr+WxASLfYWL73ZTJvxoUPP+UXVJLWDY4R6ZHzuO5ltR5BhtyuKG3BbO t17+s/jZyqPHTG96pSK5/xt5+86dFyVKvnk0/zuJQvfCPtvO6CGbivuDoEtUK+mzLs3iJLfH1/Zs0 0NMs926E8vADbUYe8KN1dlh04Xcp/iyqGwNDbzKSJ+AcYz7yrGJxIL1170xp1ZSuMXMOMpLyxn7rP v643pEOaQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kfi6e-00070O-5i; Thu, 19 Nov 2020 11:28:04 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kfi6b-0006zE-2I for linux-arm-kernel@lists.infradead.org; Thu, 19 Nov 2020 11:28:01 +0000 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 69D521396; Thu, 19 Nov 2020 03:28:00 -0800 (PST) Received: from e113632-lin (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 191BA3F718; Thu, 19 Nov 2020 03:27:57 -0800 (PST) References: <20201113093720.21106-1-will@kernel.org> <20201113093720.21106-8-will@kernel.org> <20201119091820.GA2416649@google.com> <20201119110549.GA3946@willie-the-truck> User-agent: mu4e 0.9.17; emacs 26.3 From: Valentin Schneider To: Will Deacon Subject: Re: [PATCH v3 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity In-reply-to: <20201119110549.GA3946@willie-the-truck> Date: Thu, 19 Nov 2020 11:27:55 +0000 Message-ID: MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201119_062801_250758_6702079B X-CRM114-Status: GOOD ( 15.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Juri Lelli , kernel-team@android.com, Vincent Guittot , Quentin Perret , Peter Zijlstra , Catalin Marinas , Johannes Weiner , linux-kernel@vger.kernel.org, Qais Yousef , Ingo Molnar , Li Zefan , Greg Kroah-Hartman , Marc Zyngier , Tejun Heo , Suren Baghdasaryan , Morten Rasmussen , linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 19/11/20 11:05, Will Deacon wrote: > On Thu, Nov 19, 2020 at 09:18:20AM +0000, Quentin Perret wrote: >> > @@ -1937,20 +1931,69 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, >> > * OK, since we're going to drop the lock immediately >> > * afterwards anyway. >> > */ >> > - rq = move_queued_task(rq, &rf, p, dest_cpu); >> > + rq = move_queued_task(rq, rf, p, dest_cpu); >> > } >> > out: >> > - task_rq_unlock(rq, p, &rf); >> > + task_rq_unlock(rq, p, rf); >> >> And that's a little odd to have here no? Can we move it back on the >> caller's side? > > I don't think so, unfortunately. __set_cpus_allowed_ptr_locked() can trigger > migration, so it can drop the rq lock as part of that and end up relocking a > new rq, which it also unlocks before returning. Doing the unlock in the > caller is therfore even weirder, because you'd have to return the lock > pointer or something horrible like that. > > I did add a comment about this right before the function and it's an > internal function to the scheduler so I think it's ok. > An alternative here would be to add a new SCA_RESTRICT flag for __set_cpus_allowed_ptr() (see migrate_disable() faff in tip/sched/core). Not fond of either approaches, but the flag thing would avoid this "quirk". > Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel