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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 37E5DC433E0 for ; Tue, 30 Jun 2020 06:17:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0FDFE206B6 for ; Tue, 30 Jun 2020 06:17:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hgiynQdP" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729937AbgF3GRT (ORCPT ); Tue, 30 Jun 2020 02:17:19 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:56597 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725845AbgF3GRT (ORCPT ); Tue, 30 Jun 2020 02:17:19 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1593497837; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=9+RQ+qThaJtacs4jb/OrkWyGDybA1bqNRSM4ltwc1f0=; b=hgiynQdP5neWRwjjGg2IDq5JISZSrg4QPPRKnl5cpluxA24gr+H6FyMsXR6Fp8vEfBqc+V b4TAVfi47HCgzXnyQ4hcIaa3NsCKz5N5u3HhHSh+1wPPMFa/eceZ2gITSUMydApnfqRHaO bXXZXuv7wDRgLnFg27N27lCuijkS9fY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-306-8Nb0DMCcPDGBs07zBmvtCw-1; Tue, 30 Jun 2020 02:17:15 -0400 X-MC-Unique: 8Nb0DMCcPDGBs07zBmvtCw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 86695800D5C; Tue, 30 Jun 2020 06:17:13 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.40.192.237]) by smtp.corp.redhat.com (Postfix) with SMTP id A202B5C290; Tue, 30 Jun 2020 06:17:10 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 30 Jun 2020 08:17:13 +0200 (CEST) Date: Tue, 30 Jun 2020 08:17:09 +0200 From: Oleg Nesterov To: Nicholas Piggin Cc: Andi Kleen , Davidlohr Bueso , Jan Kara , Lukas Czerner , Linux Kernel Mailing List , Mel Gorman , Peter Zijlstra , Linus Torvalds Subject: Re: wait_on_page_bit_common(TASK_KILLABLE, EXCLUSIVE) can miss wakeup? Message-ID: <20200630061708.GA21263@redhat.com> References: <20200624161142.GA12184@redhat.com> <20200624162042.GA12238@redhat.com> <20200626154313.GI4817@hirez.programming.kicks-ass.net> <1593396958.ydiznwsuu8.astroid@bobo.none> <20200629140245.GB20323@redhat.com> <1593482844.k3rh7s05o8.astroid@bobo.none> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1593482844.k3rh7s05o8.astroid@bobo.none> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/30, Nicholas Piggin wrote: > Excerpts from Oleg Nesterov's message of June 30, 2020 12:02 am: > > On 06/29, Nicholas Piggin wrote: > >> > >> prepare_to_wait_event() has a pretty good pattern (and comment), I would > >> favour using that (test the signal when inserting on the waitqueue). > >> > >> @@ -1133,6 +1133,15 @@ static inline int wait_on_page_bit_common(wait_queue_head_t *q, > >> for (;;) { > >> spin_lock_irq(&q->lock); > >> > >> + if (signal_pending_state(state, current)) { > >> + /* Must not lose an exclusive wake up, see > >> + * prepare_to_wait_event comment */ > >> + list_del_init(&wait->entry); > >> + spin_unlock_irq(&q->lock); > >> + ret = -EINTR; > > > > Basically this is what my patch in the 1st email does. But note that we can't > > just set "ret = -EINTR" here, we will need to clear "ret" if test_and_set_bit() > > below succeeds. That is why I used another "int intr" variable. > > You snipped off one more important line of context. No such games are > required AFAIKS. for (;;) { spin_lock_irq(&q->lock); + if (signal_pending_state(state, current)) { + /* Must not lose an exclusive wake up, see + * prepare_to_wait_event comment */ + list_del_init(&wait->entry); + spin_unlock_irq(&q->lock); + ret = -EINTR; + break; + } so wait_on_page_bit_common() just returns -EINTR if signal_pending_state() == T. And this is wrong if "current" was already woken up by unlock_page(). That is why ___wait_event() checks the condition even if prepare_to_wait_event() returns -EINTR. The comment in prepare_to_wait_event() tries to explain this. Oleg.