From: Josef Bacik <josef@toxicpanda.com> To: linux-btrfs@vger.kernel.org, kernel-team@fb.com Subject: [PATCH v2 2/7] btrfs: do not take the uuid_mutex in btrfs_rm_device Date: Tue, 27 Jul 2021 17:01:14 -0400 [thread overview] Message-ID: <4f7529acd33594df9b0b06f7011d8cd4d195fc29.1627419595.git.josef@toxicpanda.com> (raw) In-Reply-To: <cover.1627419595.git.josef@toxicpanda.com> We got the following lockdep splat while running xfstests (specifically btrfs/003 and btrfs/020 in a row) with the new rc. This was uncovered by 87579e9b7d8d ("loop: use worker per cgroup instead of kworker") which converted loop to using workqueues, which comes with lockdep annotations that don't exist with kworkers. The lockdep splat is as follows ====================================================== WARNING: possible circular locking dependency detected 5.14.0-rc2-custom+ #34 Not tainted ------------------------------------------------------ losetup/156417 is trying to acquire lock: ffff9c7645b02d38 ((wq_completion)loop0){+.+.}-{0:0}, at: flush_workqueue+0x84/0x600 but task is already holding lock: ffff9c7647395468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x650 [loop] which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #5 (&lo->lo_mutex){+.+.}-{3:3}: __mutex_lock+0xba/0x7c0 lo_open+0x28/0x60 [loop] blkdev_get_whole+0x28/0xf0 blkdev_get_by_dev.part.0+0x168/0x3c0 blkdev_open+0xd2/0xe0 do_dentry_open+0x163/0x3a0 path_openat+0x74d/0xa40 do_filp_open+0x9c/0x140 do_sys_openat2+0xb1/0x170 __x64_sys_openat+0x54/0x90 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #4 (&disk->open_mutex){+.+.}-{3:3}: __mutex_lock+0xba/0x7c0 blkdev_get_by_dev.part.0+0xd1/0x3c0 blkdev_get_by_path+0xc0/0xd0 btrfs_scan_one_device+0x52/0x1f0 [btrfs] btrfs_control_ioctl+0xac/0x170 [btrfs] __x64_sys_ioctl+0x83/0xb0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #3 (uuid_mutex){+.+.}-{3:3}: __mutex_lock+0xba/0x7c0 btrfs_rm_device+0x48/0x6a0 [btrfs] btrfs_ioctl+0x2d1c/0x3110 [btrfs] __x64_sys_ioctl+0x83/0xb0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #2 (sb_writers#11){.+.+}-{0:0}: lo_write_bvec+0x112/0x290 [loop] loop_process_work+0x25f/0xcb0 [loop] process_one_work+0x28f/0x5d0 worker_thread+0x55/0x3c0 kthread+0x140/0x170 ret_from_fork+0x22/0x30 -> #1 ((work_completion)(&lo->rootcg_work)){+.+.}-{0:0}: process_one_work+0x266/0x5d0 worker_thread+0x55/0x3c0 kthread+0x140/0x170 ret_from_fork+0x22/0x30 -> #0 ((wq_completion)loop0){+.+.}-{0:0}: __lock_acquire+0x1130/0x1dc0 lock_acquire+0xf5/0x320 flush_workqueue+0xae/0x600 drain_workqueue+0xa0/0x110 destroy_workqueue+0x36/0x250 __loop_clr_fd+0x9a/0x650 [loop] lo_ioctl+0x29d/0x780 [loop] block_ioctl+0x3f/0x50 __x64_sys_ioctl+0x83/0xb0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Chain exists of: (wq_completion)loop0 --> &disk->open_mutex --> &lo->lo_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&lo->lo_mutex); lock(&disk->open_mutex); lock(&lo->lo_mutex); lock((wq_completion)loop0); *** DEADLOCK *** 1 lock held by losetup/156417: #0: ffff9c7647395468 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x650 [loop] stack backtrace: CPU: 8 PID: 156417 Comm: losetup Not tainted 5.14.0-rc2-custom+ #34 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 Call Trace: dump_stack_lvl+0x57/0x72 check_noncircular+0x10a/0x120 __lock_acquire+0x1130/0x1dc0 lock_acquire+0xf5/0x320 ? flush_workqueue+0x84/0x600 flush_workqueue+0xae/0x600 ? flush_workqueue+0x84/0x600 drain_workqueue+0xa0/0x110 destroy_workqueue+0x36/0x250 __loop_clr_fd+0x9a/0x650 [loop] lo_ioctl+0x29d/0x780 [loop] ? __lock_acquire+0x3a0/0x1dc0 ? update_dl_rq_load_avg+0x152/0x360 ? lock_is_held_type+0xa5/0x120 ? find_held_lock.constprop.0+0x2b/0x80 block_ioctl+0x3f/0x50 __x64_sys_ioctl+0x83/0xb0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f645884de6b Usually the uuid_mutex exists to protect the fs_devices that map together all of the devices that match a specific uuid. In rm_device we're messing with the uuid of a device, so it makes sense to protect that here. However in doing that it pulls in a whole host of lockdep dependencies, as we call mnt_may_write() on the sb before we grab the uuid_mutex, thus we end up with the dependency chain under the uuid_mutex being added under the normal sb write dependency chain, which causes problems with loop devices. We don't need the uuid mutex here however. If we call btrfs_scan_one_device() before we scratch the super block we will find the fs_devices and not find the device itself and return EBUSY because the fs_devices is open. If we call it after the scratch happens it will not appear to be a valid btrfs file system. We do not need to worry about other fs_devices modifying operations here because we're protected by the exclusive operations locking. So drop the uuid_mutex here in order to fix the lockdep splat. Signed-off-by: Josef Bacik <josef@toxicpanda.com> --- fs/btrfs/volumes.c | 5 ----- 1 file changed, 5 deletions(-) diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 5217b93172b4..0e7372f637eb 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -2082,8 +2082,6 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path, u64 num_devices; int ret = 0; - mutex_lock(&uuid_mutex); - num_devices = btrfs_num_devices(fs_info); ret = btrfs_check_raid_min_devices(fs_info, num_devices - 1); @@ -2127,11 +2125,9 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path, mutex_unlock(&fs_info->chunk_mutex); } - mutex_unlock(&uuid_mutex); ret = btrfs_shrink_device(device, 0); if (!ret) btrfs_reada_remove_dev(device); - mutex_lock(&uuid_mutex); if (ret) goto error_undo; @@ -2215,7 +2211,6 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path, } out: - mutex_unlock(&uuid_mutex); return ret; error_undo: -- 2.26.3
next prev parent reply other threads:[~2021-07-27 21:03 UTC|newest] Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-27 21:01 [PATCH v2 0/7] Josef Bacik 2021-07-27 21:01 ` [PATCH v2 1/7] btrfs: do not call close_fs_devices in btrfs_rm_device Josef Bacik 2021-09-01 8:13 ` Anand Jain 2021-07-27 21:01 ` Josef Bacik [this message] 2021-09-01 12:01 ` [PATCH v2 2/7] btrfs: do not take the uuid_mutex " Anand Jain 2021-09-01 17:08 ` David Sterba 2021-09-01 17:10 ` Josef Bacik 2021-09-01 19:49 ` Anand Jain 2021-09-02 12:58 ` David Sterba 2021-09-02 14:10 ` Josef Bacik 2021-09-17 14:33 ` David Sterba 2021-09-20 7:45 ` Anand Jain 2021-09-20 8:26 ` David Sterba 2021-09-20 9:41 ` Anand Jain 2021-09-23 4:33 ` Anand Jain 2021-09-21 11:59 ` Filipe Manana 2021-09-21 12:17 ` Filipe Manana 2021-09-22 15:33 ` Filipe Manana 2021-09-23 4:15 ` Anand Jain 2021-09-23 3:58 ` [PATCH] btrfs: drop lockdep assert in close_fs_devices() Anand Jain 2021-09-23 4:04 ` Anand Jain 2021-07-27 21:01 ` [PATCH v2 3/7] btrfs: do not read super look for a device path Josef Bacik 2021-08-25 2:00 ` Anand Jain 2021-09-27 15:32 ` Josef Bacik 2021-09-28 11:50 ` Anand Jain 2021-07-27 21:01 ` [PATCH v2 4/7] btrfs: update the bdev time directly when closing Josef Bacik 2021-08-25 0:35 ` Anand Jain 2021-09-02 12:16 ` David Sterba 2021-07-27 21:01 ` [PATCH v2 5/7] btrfs: delay blkdev_put until after the device remove Josef Bacik 2021-08-25 1:00 ` Anand Jain 2021-09-02 12:16 ` David Sterba 2021-07-27 21:01 ` [PATCH v2 6/7] btrfs: unify common code for the v1 and v2 versions of " Josef Bacik 2021-08-25 1:19 ` Anand Jain 2021-09-01 14:05 ` Nikolay Borisov 2021-07-27 21:01 ` [PATCH v2 7/7] btrfs: do not take the device_list_mutex in clone_fs_devices Josef Bacik 2021-08-24 22:08 ` Anand Jain 2021-09-01 13:35 ` Nikolay Borisov 2021-09-02 12:59 ` David Sterba 2021-09-17 15:06 ` [PATCH v2 0/7] David Sterba
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