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=-10.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 C026CC6369E for ; Thu, 19 Nov 2020 11:07:20 +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 46E76246F1 for ; Thu, 19 Nov 2020 11:07:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="HtVFU5n+"; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="n/vkPFNc" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 46E76246F1 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org 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:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=X+k4wHHct7kC/bYq3D71V5i4MZUdFb9ldcdwkZ+PJmI=; b=HtVFU5n+2PshSxjdyxr+9oW50 HMbq0/xDA2F3RedlGcqPQ60syI3sOBAOmkdGpBwSfpF5deAiqoP8jEyl7wz0c1CRYCNn3r2PnK+rT 9J8m3OuLE0NWrDn9ZcYKu+Mc7rc3PkNEyI4yqPr8MQzigNhdvQp02+CPZc02tDnANYMAO4+swnzSm GpYq2weeNfDdjDhcvxx1JQ5hlFk7TjWMAxG6zasgYBX/prFr8U/f47Qg0WTiJ2QnbW3udl1HcOu4d 2sHHwO1TMXpvStdSAUctdgP9Upyxyhh54QIh+q0xCvhXOcbdsQTbCbGK1spBuHPORmlAqLrwZIbXa kJoBw8VSg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kfhlJ-0002wI-QC; Thu, 19 Nov 2020 11:06:02 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kfhlG-0002v9-18 for linux-arm-kernel@lists.infradead.org; Thu, 19 Nov 2020 11:05:59 +0000 Received: from willie-the-truck (236.31.169.217.in-addr.arpa [217.169.31.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 87C2E22248; Thu, 19 Nov 2020 11:05:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1605783956; bh=g83zsAw1L28Dyy0iuhil8dhaCafVEDeI9B1H3qU4DZU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=n/vkPFNcUf0qbzgqywiSVqIg3KVXiJf4OZLpfdIZ+Hky6gQYMGlzS/fdpzAnZqbmE HY4SrEH60JXO2yQgRZjAAgNAaOhhL0WbRP5oTFnXWi+kmAWvUYxybQlxc6GWf7p2q4 ihMVUefWCVk9PgS72ftqBHXduUh2yF1VwMnIaQl8= Date: Thu, 19 Nov 2020 11:05:50 +0000 From: Will Deacon To: Quentin Perret Subject: Re: [PATCH v3 07/14] sched: Introduce restrict_cpus_allowed_ptr() to limit task CPU affinity Message-ID: <20201119110549.GA3946@willie-the-truck> References: <20201113093720.21106-1-will@kernel.org> <20201113093720.21106-8-will@kernel.org> <20201119091820.GA2416649@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20201119091820.GA2416649@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201119_060558_370378_6CD82FF2 X-CRM114-Status: GOOD ( 22.31 ) 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, Marc Zyngier , kernel-team@android.com, Vincent Guittot , Juri Lelli , Ingo Molnar , Peter Zijlstra , Catalin Marinas , Johannes Weiner , linux-kernel@vger.kernel.org, Qais Yousef , Li Zefan , Greg Kroah-Hartman , 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 Hi Quentin, Thanks for having a look. On Thu, Nov 19, 2020 at 09:18:20AM +0000, Quentin Perret wrote: > On Friday 13 Nov 2020 at 09:37:12 (+0000), Will Deacon wrote: > > -static int __set_cpus_allowed_ptr(struct task_struct *p, > > - const struct cpumask *new_mask, bool check) > > +static int __set_cpus_allowed_ptr_locked(struct task_struct *p, > > + const struct cpumask *new_mask, > > + bool check, > > + struct rq *rq, > > + struct rq_flags *rf) > > { > > const struct cpumask *cpu_valid_mask = cpu_active_mask; > > unsigned int dest_cpu; > > - struct rq_flags rf; > > - struct rq *rq; > > int ret = 0; > > Should we have a lockdep assertion here? I pondered that, but I don't think it's necessary because we already have one in do_set_cpus_allowed() so adding an extra one here doesn't really add anything. > > - rq = task_rq_lock(p, &rf); > > update_rq_clock(rq); > > > > if (p->flags & PF_KTHREAD) { > > @@ -1929,7 +1923,7 @@ static int __set_cpus_allowed_ptr(struct task_struct *p, > > if (task_running(rq, p) || p->state == TASK_WAKING) { > > struct migration_arg arg = { p, dest_cpu }; > > /* Need help from migration thread: drop lock and wait. */ > > - task_rq_unlock(rq, p, &rf); > > + task_rq_unlock(rq, p, rf); > > stop_one_cpu(cpu_of(rq), migration_cpu_stop, &arg); > > return 0; > > } else if (task_on_rq_queued(p)) { > > @@ -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. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel