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=-13.2 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 5E50EC433DB for ; Thu, 11 Feb 2021 11:29:04 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id E2409601FF for ; Thu, 11 Feb 2021 11:29:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E2409601FF Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 71F5C6B00CC; Thu, 11 Feb 2021 06:29:03 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6A7FE6B00CD; Thu, 11 Feb 2021 06:29:03 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 597846B00CE; Thu, 11 Feb 2021 06:29:03 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0150.hostedemail.com [216.40.44.150]) by kanga.kvack.org (Postfix) with ESMTP id 40BB16B00CC for ; Thu, 11 Feb 2021 06:29:03 -0500 (EST) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id EF7FD8249980 for ; Thu, 11 Feb 2021 11:29:02 +0000 (UTC) X-FDA: 77805765324.30.brass30_5b0857a27618 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin30.hostedemail.com (Postfix) with ESMTP id CAF7E180B3C83 for ; Thu, 11 Feb 2021 11:29:02 +0000 (UTC) X-HE-Tag: brass30_5b0857a27618 X-Filterd-Recvd-Size: 8256 Received: from mail-qv1-f49.google.com (mail-qv1-f49.google.com [209.85.219.49]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Thu, 11 Feb 2021 11:29:02 +0000 (UTC) Received: by mail-qv1-f49.google.com with SMTP id p12so2365465qvv.5 for ; Thu, 11 Feb 2021 03:29:02 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=9E3U2WsJbq5lq+cPvO75ifdr6pZnfAuKCKnYnoT37Hs=; b=aO6XwrM+laoJC+TCRRsc/llmw64ZusSVPcXSU1eS58RDSiICiFAavqWJ1+wlUPqUW2 gzfWDAoxIccXHnGSoMILAHuh+q9ojnijdnkRpRlGstFkQsaD0RAwfEycZNzD+U6YWg2a zG/56nihol+8HG+odjT6QBHMuShFVKcvzXVEsaBsrxjaRBqhe7axNHOBLt+giAzfcc1k D5RmPt5t72l8/9HN3RlXWqXHkySsNN0vYlcAXHjBvVxPjhcfHrjdGJp7heDMaXxnetOk OACCvQ0CvgnQyCUhZZzx4SO2QHlgOyf3wcXGLntNj2Xq0QlgicEQV1vqfl6PI+gjwkoa 6s2Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=9E3U2WsJbq5lq+cPvO75ifdr6pZnfAuKCKnYnoT37Hs=; b=T7ZhFWyaELPioXVG0Hdhp6uxECG/F4n6TdNvpIJGNRImt3hV/9+VyHnxXinu39qv0D zRVe1qDIXlzkGeYwWlq/b35104MXC3mjpSVjwYeWrbEbMkDfjQo98g2K2SaqJK6L7GlF GI9f/XUtHcR5y76VgHtnkAzWtZ4Uvnq7YoIjuSph5txHe+6zCXW71D46W82nRLJhOjxE /Kle4oJbSwOOuTVSVcWCwNQOTZoQDr1hxN1E1/buEpGdferljG+lYjBbgPRpkkE616NI Mcb1gMqlFVw84EMMYttYoAffF+2rPnZTPhf386/R7WWBz+7UFbAWrOig5gAET/r8kA2T zENw== X-Gm-Message-State: AOAM531+uyXOXKmlZqFJ+yY3zHRo7PjeTDIGT0wZR2OHB4FlV8utZYzs lWB9MS0lFkb6k+aBCKSDznq0Rm956nvNeQkpWUASWw== X-Google-Smtp-Source: ABdhPJzSFLQhssC/M3MzzqWhnULkeF3G/ieVd61jjCYgo3R+1BGFt9YIkm79Z4L7Etcq6JETSdaWeJm5sJTxKCb+US0= X-Received: by 2002:a05:6214:1ca:: with SMTP id c10mr6814571qvt.44.1613042941490; Thu, 11 Feb 2021 03:29:01 -0800 (PST) MIME-Version: 1.0 References: <000000000000563a0205bafb7970@google.com> <20210211104947.GL19070@quack2.suse.cz> In-Reply-To: From: Dmitry Vyukov Date: Thu, 11 Feb 2021 12:28:48 +0100 Message-ID: Subject: Re: possible deadlock in start_this_handle (2) To: Jan Kara Cc: syzbot , Jan Kara , linux-ext4@vger.kernel.org, LKML , syzkaller-bugs , "Theodore Ts'o" , Michal Hocko , Linux-MM Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Feb 11, 2021 at 12:22 PM Dmitry Vyukov wrote: > > On Thu, Feb 11, 2021 at 11:49 AM Jan Kara wrote: > > > > Hello, > > > > added mm guys to CC. > > > > On Wed 10-02-21 05:35:18, syzbot wrote: > > > HEAD commit: 1e0d27fc Merge branch 'akpm' (patches from Andrew) > > > git tree: upstream > > > console output: https://syzkaller.appspot.com/x/log.txt?x=15cbce90d00000 > > > kernel config: https://syzkaller.appspot.com/x/.config?x=bd1f72220b2e57eb > > > dashboard link: https://syzkaller.appspot.com/bug?extid=bfdded10ab7dcd7507ae > > > userspace arch: i386 > > > > > > Unfortunately, I don't have any reproducer for this issue yet. > > > > > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > > > Reported-by: syzbot+bfdded10ab7dcd7507ae@syzkaller.appspotmail.com > > > > > > ====================================================== > > > WARNING: possible circular locking dependency detected > > > 5.11.0-rc6-syzkaller #0 Not tainted > > > ------------------------------------------------------ > > > kswapd0/2246 is trying to acquire lock: > > > ffff888041a988e0 (jbd2_handle){++++}-{0:0}, at: start_this_handle+0xf81/0x1380 fs/jbd2/transaction.c:444 > > > > > > but task is already holding lock: > > > ffffffff8be892c0 (fs_reclaim){+.+.}-{0:0}, at: __fs_reclaim_acquire+0x0/0x30 mm/page_alloc.c:5195 > > > > > > which lock already depends on the new lock. > > > > > > the existing dependency chain (in reverse order) is: > > > > > > -> #2 (fs_reclaim){+.+.}-{0:0}: > > > __fs_reclaim_acquire mm/page_alloc.c:4326 [inline] > > > fs_reclaim_acquire+0x117/0x150 mm/page_alloc.c:4340 > > > might_alloc include/linux/sched/mm.h:193 [inline] > > > slab_pre_alloc_hook mm/slab.h:493 [inline] > > > slab_alloc_node mm/slub.c:2817 [inline] > > > __kmalloc_node+0x5f/0x430 mm/slub.c:4015 > > > kmalloc_node include/linux/slab.h:575 [inline] > > > kvmalloc_node+0x61/0xf0 mm/util.c:587 > > > kvmalloc include/linux/mm.h:781 [inline] > > > ext4_xattr_inode_cache_find fs/ext4/xattr.c:1465 [inline] > > > ext4_xattr_inode_lookup_create fs/ext4/xattr.c:1508 [inline] > > > ext4_xattr_set_entry+0x1ce6/0x3780 fs/ext4/xattr.c:1649 > > > ext4_xattr_ibody_set+0x78/0x2b0 fs/ext4/xattr.c:2224 > > > ext4_xattr_set_handle+0x8f4/0x13e0 fs/ext4/xattr.c:2380 > > > ext4_xattr_set+0x13a/0x340 fs/ext4/xattr.c:2493 > > > ext4_xattr_user_set+0xbc/0x100 fs/ext4/xattr_user.c:40 > > > __vfs_setxattr+0x10e/0x170 fs/xattr.c:177 > > > __vfs_setxattr_noperm+0x11a/0x4c0 fs/xattr.c:208 > > > __vfs_setxattr_locked+0x1bf/0x250 fs/xattr.c:266 > > > vfs_setxattr+0x135/0x320 fs/xattr.c:291 > > > setxattr+0x1ff/0x290 fs/xattr.c:553 > > > path_setxattr+0x170/0x190 fs/xattr.c:572 > > > __do_sys_setxattr fs/xattr.c:587 [inline] > > > __se_sys_setxattr fs/xattr.c:583 [inline] > > > __ia32_sys_setxattr+0xbc/0x150 fs/xattr.c:583 > > > do_syscall_32_irqs_on arch/x86/entry/common.c:77 [inline] > > > __do_fast_syscall_32+0x56/0x80 arch/x86/entry/common.c:139 > > > do_fast_syscall_32+0x2f/0x70 arch/x86/entry/common.c:164 > > > entry_SYSENTER_compat_after_hwframe+0x4d/0x5c > > > > This stacktrace should never happen. ext4_xattr_set() starts a transaction. > > That internally goes through start_this_handle() which calls: > > > > handle->saved_alloc_context = memalloc_nofs_save(); > > > > and we restore the allocation context only in stop_this_handle() when > > stopping the handle. And with this fs_reclaim_acquire() should remove > > __GFP_FS from the mask and not call __fs_reclaim_acquire(). > > > > Now I have no idea why something here didn't work out. Given we don't have > > a reproducer it will be probably difficult to debug this. I'd note that > > about year and half ago similar report happened (got autoclosed) so it may > > be something real somewhere but it may also be just some HW glitch or > > something like that. > > HW glitch is theoretically possible. But if we are considering such > causes, I would say a kernel memory corruption is way more likely, we > have hundreds of known memory-corruption-capable bugs open. In most > cases they are caught by KASAN before doing silent damage. But KASAN > can miss some cases. > > I see at least 4 existing bugs with similar stack: > https://syzkaller.appspot.com/bug?extid=bfdded10ab7dcd7507ae > https://syzkaller.appspot.com/bug?extid=a7ab8df042baaf42ae3c > https://syzkaller.appspot.com/bug?id=c814a55a728493959328551c769ede4c8ff72aab > https://syzkaller.appspot.com/bug?id=426ad9adca053dafcd698f3a48ad5406dccc972b > > All in all, I would not assume it's a memory corruption. When we had > bugs that actually caused silent memory corruption, that caused a > spike of random one-time crashes all over the kernel. This does not > look like it. I wonder if memalloc_nofs_save (or any other manipulation of current->flags) could have been invoked from interrupt context? I think it could cause the failure mode we observe (extremely rare disappearing flags). It may be useful to add a check for task context there.