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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1E6C6C433EF for ; Fri, 15 Jul 2022 01:39:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232930AbiGOBjO (ORCPT ); Thu, 14 Jul 2022 21:39:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36612 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232310AbiGOBjN (ORCPT ); Thu, 14 Jul 2022 21:39:13 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9613242AD4 for ; Thu, 14 Jul 2022 18:39:11 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id e63-20020a253742000000b0066e1afdb46aso2943642yba.1 for ; Thu, 14 Jul 2022 18:39:11 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=mAeXqOZZBVPdbq4yhQiUP5VN0GJajqrt77b0GTm8ddQ=; b=JfY/dZhiys1bZY5EGSfSj6NS3oNMqRabw0VWDSE9yIeZMDLkSZqc+2FvMnzpS4MNgZ XOFzz5TtApvGzeW/vTh65Ag9cCAWr3OBzN4gAv4CDkN+voEmvI9EdsHqA7vo7vvm4OyG kgPnXqIerO7mSCxfm6ZLl7CSkBrXFSl32yXeRbVtior4ZdkP6BQJmSFZqNdYcm3LxDyl j9UFszpl2EpD+Pge2UyrwQcfprrMB0rwLkicdT4Eeak3RDQO1ugIpwyxBjErKRLN+CEp XJMbd3u4sWaJP27ptJxp7gFOIRpGqWZVCj56XMU8IayCbz29K0X7EcS9njUklygLxjva DvLQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=mAeXqOZZBVPdbq4yhQiUP5VN0GJajqrt77b0GTm8ddQ=; b=6RMH7rRuEPq6S/i7xM7GIS7Nrd6VeT1PvVjN7WgkYWDNB72T2ipDtXIJR5ip460+S2 PUa04L2EPdA73G+FLyKbNKZpPW96jyKBGfpgr1WTPJiECq5JsfNIyOmQuHfhGlUL1pya lsGqpeaYvrX2gLegueTnNagYwGx6oTuPjq9V1gIjc3AATD5b6cVNAKqh2SqZ6F+vuaG1 8ojAynVi6fwsCy3yzRz/zACcqf0Gl2EQNGJ3168FKnENY9b0WFcCroQpasHlNwsk8fjP 5tg63iAZnYQ8o0rV/sq75UtvRJZkswTlsPGf+DoSs+34VnKh8OJRlgsU3lseL2yBMpBs 2Tyg== X-Gm-Message-State: AJIora8NVU705keQ89SOFuuv3avjLklXWhkQuHYrbCN52HmH9SzwVVmo PI6xOPL8kqIEMEijkXCjfRMO1oQcyFV+Nw== X-Google-Smtp-Source: AGRyM1twMADmukVDHq0OwkYLBQBbC2d2LlX8VOPaRlImf1uqHpMX5qVQPJ25TQtBfNyXY015rkJIjGLC0J2OxQ== X-Received: from shakeelb.c.googlers.com ([fda3:e722:ac3:cc00:20:ed76:c0a8:28b]) (user=shakeelb job=sendgmr) by 2002:a25:a2ca:0:b0:66e:719e:279 with SMTP id c10-20020a25a2ca000000b0066e719e0279mr11067587ybn.622.1657849150783; Thu, 14 Jul 2022 18:39:10 -0700 (PDT) Date: Fri, 15 Jul 2022 01:39:08 +0000 In-Reply-To: <534fa596-0c29-0f1e-b292-53ad9c3dbbe3@I-love.SAKURA.ne.jp> Message-Id: <20220715013908.ayyimue5yhfwonho@google.com> Mime-Version: 1.0 References: <000000000000471c2905e3c2c2c2@google.com> <20220714141813.yi5p4o2tiyvkao6b@quack3> <534fa596-0c29-0f1e-b292-53ad9c3dbbe3@I-love.SAKURA.ne.jp> Subject: Re: [syzbot] possible deadlock in start_this_handle (3) From: Shakeel Butt To: Tetsuo Handa Cc: Jan Kara , linux-mm@kvack.org, jack@suse.com, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com, tytso@mit.edu, linux-fsdevel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, Jul 15, 2022 at 07:24:55AM +0900, Tetsuo Handa wrote: > On 2022/07/14 23:18, Jan Kara wrote: > > Hello, > > > > so this lockdep report looks real but is more related to OOM handling than > > to ext4 as such. The immediate problem I can see is that > > mem_cgroup_print_oom_meminfo() which is called under oom_lock calls > > memory_stat_format() which does GFP_KERNEL allocations to allocate buffers > > for dumping of MM statistics. This creates oom_lock -> fs reclaim > > dependency and because OOM can be hit (and thus oom_lock acquired) in > > practically any allocation (regardless of GFP_NOFS) this has a potential of > > creating real deadlock cycles. > > > > So should mem_cgroup_print_oom_meminfo() be using > > memalloc_nofs_save/restore() to avoid such deadlocks? Or perhaps someone > > sees another solution? Generally allocating memory to report OOM looks a > > bit dangerous to me ;). mem_cgroup_print_oom_meminfo() is called only for memcg OOMs. So, the situaion would be dangerous only if the system is also OOM at that time. > > > > Honza > > I think mem_cgroup_print_oom_meminfo() should use GFP_ATOMIC, for it will fall into > infinite loop if kmalloc(GFP_NOFS) under oom_lock reached __alloc_pages_may_oom() path. I would prefer GFP_NOWAIT. This is printing info for memcg OOMs and if the system is low on memory then memcg OOMs has lower importance than the system state.