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=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_MUTT 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 693C3C04AB5 for ; Mon, 3 Jun 2019 12:44:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4244C27EBE for ; Mon, 3 Jun 2019 12:44:13 +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="kNNcDuFg" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728136AbfFCMoM (ORCPT ); Mon, 3 Jun 2019 08:44:12 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:58728 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728083AbfFCMoJ (ORCPT ); Mon, 3 Jun 2019 08:44:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=GNP3D276BFtDK39lLo6rJPWpnwlFMjiWsjF1eSRNq9k=; b=kNNcDuFgjSY3vB9kQuAo8Ap2W LZjW6ej3axV9mqJfEPOQFrK+BxXkmgewzcyXkXEFQ+hm/CEJTLQGKgVTB5n8CAXGs7hKVoBe6o+pD NVaeCspnEij+mfEOtozvjOHEcxOtjBcWqhpbjaxRfUU87KZ+f0jBRMoRfpzzjfMHRhzDmN5dDbvY5 hlb6vN8a82YFI3+tI26fcMhxrMjTfMYk7TH61euKay+ArCHXVntMUgrvk28lZR4AlDs9wrqOPLlyv R4QthQrORiZVlXpb3A5eNEt+oucLFWpIKVIvVP+yiz9BLLHGzskGur/XNFIBDQGswlMoikfSWafKe meD4M2llg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hXmJn-0004ug-CU; Mon, 03 Jun 2019 12:44:03 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B738F20274AFF; Mon, 3 Jun 2019 14:44:01 +0200 (CEST) Date: Mon, 3 Jun 2019 14:44:01 +0200 From: Peter Zijlstra To: Jens Axboe Cc: Qian Cai , akpm@linux-foundation.org, hch@lst.de, oleg@redhat.com, gkohli@codeaurora.org, mingo@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] block: fix a crash in do_task_dead() Message-ID: <20190603124401.GB3463@hirez.programming.kicks-ass.net> References: <1559161526-618-1-git-send-email-cai@lca.pw> <20190530080358.GG2623@hirez.programming.kicks-ass.net> <82e88482-1b53-9423-baad-484312957e48@kernel.dk> <20190603123705.GB3419@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190603123705.GB3419@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 03, 2019 at 02:37:05PM +0200, Peter Zijlstra wrote: > Anyway, Oleg, do you see anything blatantly buggered with this patch? > > (the stats were already dodgy for rq-stats, this patch makes them dodgy > for task-stats too) It now also has concurrency on wakeup; but afaict that's harmless, we'll get racing stores of p->state = TASK_RUNNING, much the same as if there was a remote wakeup vs a wait-loop terminating early. I suppose the tracepoint consumers might have to deal with some artifacts there, but that's their problem. > --- > kernel/sched/core.c | 38 ++++++++++++++++++++++++++++++++------ > 1 file changed, 32 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 102dfcf0a29a..474aa4c8e9d2 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1990,6 +1990,28 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > unsigned long flags; > int cpu, success = 0; > > + if (p == current) { > + /* > + * We're waking current, this means 'p->on_rq' and 'task_cpu(p) > + * == smp_processor_id()'. Together this means we can special > + * case the whole 'p->on_rq && ttwu_remote()' case below > + * without taking any locks. > + * > + * In particular: > + * - we rely on Program-Order guarantees for all the ordering, > + * - we're serialized against set_special_state() by virtue of > + * it disabling IRQs (this allows not taking ->pi_lock). > + */ > + if (!(p->state & state)) > + goto out; > + > + success = 1; > + trace_sched_waking(p); > + p->state = TASK_RUNNING; > + trace_sched_woken(p); > + goto out; > + } > + > /* > * If we are going to wake up a thread waiting for CONDITION we > * need to ensure that CONDITION=1 done by the caller can not be > @@ -1999,7 +2021,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > raw_spin_lock_irqsave(&p->pi_lock, flags); > smp_mb__after_spinlock(); > if (!(p->state & state)) > - goto out; > + goto unlock; > > trace_sched_waking(p); > > @@ -2029,7 +2051,7 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > */ > smp_rmb(); > if (p->on_rq && ttwu_remote(p, wake_flags)) > - goto stat; > + goto unlock; > > #ifdef CONFIG_SMP > /* > @@ -2089,12 +2111,16 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > #endif /* CONFIG_SMP */ > > ttwu_queue(p, cpu, wake_flags); > -stat: > - ttwu_stat(p, cpu, wake_flags); > -out: > +unlock: > raw_spin_unlock_irqrestore(&p->pi_lock, flags); > > - return success; > +out: > + if (success) { > + ttwu_stat(p, cpu, wake_flags); > + return true; > + } > + > + return false; > } > > /**