On Tue, Sep 10, 2024 at 11:07:13AM GMT, Chao Yu wrote: > syzbot reports a f2fs bug as below: > > ------------[ cut here ]------------ > WARNING: CPU: 1 PID: 58 at kernel/rcu/sync.c:177 rcu_sync_dtor+0xcd/0x180 > kernel/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 |= 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=remount-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@brauner > [2] https://lore.kernel.org/all/20240729132721.hxih6ehigadqf7wx@quack3 > [3] https://lore.kernel.org/linux-ext4/20240805201241.27286-1-j...@suse.cz > > Fixes: b62e71be2110 ("f2fs: support errors=remount-ro|continue|panic > mountoption") > Reported-by: syzbot+20d7e439f76bbbd86...@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/all/000000000000b90a8e061e21d...@google.com/ > Cc: Jan Kara <j...@suse.cz> > Cc: Christian Brauner <brau...@kernel.org> > Signed-off-by: Chao Yu <c...@kernel.org> > ---
Thanks! Reviewed-by: Christian Brauner <brau...@kernel.org> _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
