From nobody Sat Nov 30 10:46:08 2024 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0E5381514E4 for ; Tue, 10 Sep 2024 03:07:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725937648; cv=none; b=lFC5l+MW7frtRa2N+HgnO6Cpz8Q3hIAPO9rJlj3bSuieNMqwxgFFXmRGvwVm3qsWvmesCB9P90upPT5GhbZUl2bBhmHDaeFVM3llD0oSszfiNO/j8rfYMT9SeSrzPRUD3T41c0cpZfeFt60eXjq5JBxy4RictHD8h9p471Ae1G8= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1725937648; c=relaxed/simple; bh=BGcgohLjLuZmmBluZnoPhK7PAf91cjVeYnh47tUQo30=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=Xn6RcgSOeadgAIvh0RRcPlRP7Thul/UB1nGLIWHPPX2N/qFG+/bsgh+ibPOgJb62qof67GnUa8H9zZZ8g1rh065qXhB5vaw+kKz8+7+6toy9FxXnlvCQ8lAtY7Pn4zDlZjRffFu3n8o3LreG+9MoN4jiHkPX8+y6vLRPPj8fWk4= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OPHp4gQD; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OPHp4gQD" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B3D07C4CEC6; Tue, 10 Sep 2024 03:07:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1725937647; bh=BGcgohLjLuZmmBluZnoPhK7PAf91cjVeYnh47tUQo30=; h=From:To:Cc:Subject:Date:From; b=OPHp4gQDpEU4HHh2lgL8dNF2qkRGXRAat+q9dZFDJAfnXL2yrmw3NhUSjNg6xPkVn rDbK8RkHcCVdNE457CuXfYcy7TtWknJKd0gTiPeBKNsYDgt81yQ5v+DVYeChXXgL5k FTibT04T25uK8S6+EF8XpTOTJ9QYY9sMgti/wHbeAnGBBflvpEr9nScDaKHEFotEjX FHnlVidC1MSQhOpaZqJZgu8MKHZN+qCswhy4wtmsm82VW/rzaanTo/KHdGIKRdF0Pe cBWLJmOZrsy6hqW70wRXbl9wMzz+yNnT2mqW2iaUrZwxNa1y2SxRmlXHSgBuBDNwSI 1CVIlWvy1agiw== From: Chao Yu To: jaegeuk@kernel.org Cc: linux-f2fs-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org, Chao Yu , syzbot+20d7e439f76bbbd863a7@syzkaller.appspotmail.com, Jan Kara , Christian Brauner Subject: [PATCH] f2fs: fix to don't set SB_RDONLY in f2fs_handle_critical_error() Date: Tue, 10 Sep 2024 11:07:13 +0800 Message-Id: <20240910030713.3716318-1-chao@kernel.org> X-Mailer: git-send-email 2.40.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" syzbot reports a f2fs bug as below: Reported-by: syzbot+20d7e439f76bbbd863a7@syzkaller.appspotmail.com Reviewed-by: Christian Brauner ------------[ cut here ]------------ WARNING: CPU: 1 PID: 58 at kernel/rcu/sync.c:177 rcu_sync_dtor+0xcd/0x180 k= ernel/rcu/sync.c:177 CPU: 1 UID: 0 PID: 58 Comm: kworker/1:2 Not tainted 6.10.0-syzkaller-12562-= g1722389b0d86 #0 Workqueue: events destroy_super_work RIP: 0010:rcu_sync_dtor+0xcd/0x180 kernel/rcu/sync.c:177 Call Trace: percpu_free_rwsem+0x41/0x80 kernel/locking/percpu-rwsem.c:42 destroy_super_work+0xec/0x130 fs/super.c:282 process_one_work kernel/workqueue.c:3231 [inline] process_scheduled_works+0xa2c/0x1830 kernel/workqueue.c:3312 worker_thread+0x86d/0xd40 kernel/workqueue.c:3390 kthread+0x2f0/0x390 kernel/kthread.c:389 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244 As Christian Brauner pointed out [1]: the root cause is f2fs sets SB_RDONLY flag in internal function, rather than setting the flag covered w/ sb->s_umount semaphore via remount procedure, then below race condition causes this bug: - freeze_super() - sb_wait_write(sb, SB_FREEZE_WRITE) - sb_wait_write(sb, SB_FREEZE_PAGEFAULT) - sb_wait_write(sb, SB_FREEZE_FS) - f2fs_handle_critical_error - sb->s_flags |=3D SB_RDONLY - thaw_super - thaw_super_locked - sb_rdonly() is true, so it skips sb_freeze_unlock(sb, SB_FREEZE_FS) - deactivate_locked_super Since f2fs has almost the same logic as ext4 [2] when handling critical error in filesystem if it mounts w/ errors=3Dremount-ro option: - set CP_ERROR_FLAG flag which indicates filesystem is stopped - record errors to superblock - set SB_RDONLY falg Once we set CP_ERROR_FLAG flag, all writable interfaces can detect the flag and stop any further updates on filesystem. So, it is safe to not set SB_RDONLY flag, let's remove the logic and keep in line w/ ext4 [3]. [1] https://lore.kernel.org/all/20240729-himbeeren-funknetz-96e62f9c7aee@br= auner [2] https://lore.kernel.org/all/20240729132721.hxih6ehigadqf7wx@quack3 [3] https://lore.kernel.org/linux-ext4/20240805201241.27286-1-jack@suse.cz Fixes: b62e71be2110 ("f2fs: support errors=3Dremount-ro|continue|panic moun= toption") Reported-by: syzbot+20d7e439f76bbbd863a7@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/000000000000b90a8e061e21d12f@google.com/ Cc: Jan Kara Cc: Christian Brauner Signed-off-by: Chao Yu --- fs/f2fs/super.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c index e774bdf875b2..acfd000c6bb0 100644 --- a/fs/f2fs/super.c +++ b/fs/f2fs/super.c @@ -4207,12 +4207,14 @@ void f2fs_handle_critical_error(struct f2fs_sb_info= *sbi, unsigned char reason, } =20 f2fs_warn(sbi, "Remounting filesystem read-only"); + /* - * Make sure updated value of ->s_mount_flags will be visible before - * ->s_flags update + * We have already set CP_ERROR_FLAG flag to stop all updates + * to filesystem, so it doesn't need to set SB_RDONLY flag here + * because the flag should be set covered w/ sb->s_umount semaphore + * via remount procedure, otherwise, it will confuse code like + * freeze_super() which will lead to deadlocks and other problems. */ - smp_wmb(); - sb->s_flags |=3D SB_RDONLY; } =20 static void f2fs_record_error_work(struct work_struct *work) --=20 2.40.1