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=-2.3 required=3.0 tests=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 96C6EC433FF for ; Fri, 9 Aug 2019 11:30:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 725C121783 for ; Fri, 9 Aug 2019 11:30:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2405723AbfHILaF (ORCPT ); Fri, 9 Aug 2019 07:30:05 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33476 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2406588AbfHILaE (ORCPT ); Fri, 9 Aug 2019 07:30:04 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6A1313172D8C; Fri, 9 Aug 2019 11:30:04 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (file01.intranet.prod.int.rdu2.redhat.com [10.11.5.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A74677E51; Fri, 9 Aug 2019 11:30:01 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (localhost [127.0.0.1]) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4) with ESMTP id x79BU1n9032319; Fri, 9 Aug 2019 07:30:01 -0400 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id x79BU0Ct032315; Fri, 9 Aug 2019 07:30:01 -0400 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Fri, 9 Aug 2019 07:30:00 -0400 (EDT) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Dave Chinner cc: Alexander Viro , "Darrick J. Wong" , Mike Snitzer , junxiao.bi@oracle.com, dm-devel@redhat.com, Alasdair Kergon , honglei.wang@oracle.com, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH] direct-io: use GFP_NOIO to avoid deadlock In-Reply-To: <20190809013403.GY7777@dread.disaster.area> Message-ID: References: <20190809013403.GY7777@dread.disaster.area> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.41]); Fri, 09 Aug 2019 11:30:04 +0000 (UTC) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, 9 Aug 2019, Dave Chinner wrote: > And, FWIW, there's an argument to be made here that the underlying > bug is dm_bufio_shrink_scan() blocking kswapd by waiting on IO > completions while holding a mutex that other IO-level reclaim > contexts require to make progress. > > Cheers, > > Dave. The IO-level reclaim contexts should use GFP_NOIO. If the dm-bufio shrinker is called with GFP_NOIO, it cannot be blocked by kswapd, because: * it uses trylock to acquire the mutex * it doesn't attempt to free buffers that are dirty or under I/O (see __try_evict_buffer) I think that this logic is sufficient to prevent the deadlock. Mikulas