From: Josef Bacik josef@toxicpanda.com
[ Upstream commit 3fa421dedbc82f985f030c5a6480ea2d784334c3 ]
When removing the device we call blkdev_put() on the device once we've removed it, and because we have an EXCL open we need to take the ->open_mutex on the block device to clean it up. Unfortunately during device remove we are holding the sb writers lock, which results in the following lockdep splat:
====================================================== WARNING: possible circular locking dependency detected 5.14.0-rc2+ #407 Not tainted ------------------------------------------------------ losetup/11595 is trying to acquire lock: ffff973ac35dd138 ((wq_completion)loop0){+.+.}-{0:0}, at: flush_workqueue+0x67/0x5e0
but task is already holding lock: ffff973ac9812c68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop]
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #4 (&lo->lo_mutex){+.+.}-{3:3}: __mutex_lock+0x7d/0x750 lo_open+0x28/0x60 [loop] blkdev_get_whole+0x25/0xf0 blkdev_get_by_dev.part.0+0x168/0x3c0 blkdev_open+0xd2/0xe0 do_dentry_open+0x161/0x390 path_openat+0x3cc/0xa20 do_filp_open+0x96/0x120 do_sys_openat2+0x7b/0x130 __x64_sys_openat+0x46/0x70 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae
-> #3 (&disk->open_mutex){+.+.}-{3:3}: __mutex_lock+0x7d/0x750 blkdev_put+0x3a/0x220 btrfs_rm_device.cold+0x62/0xe5 btrfs_ioctl+0x2a31/0x2e70 __x64_sys_ioctl+0x80/0xb0 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae
-> #2 (sb_writers#12){.+.+}-{0:0}: lo_write_bvec+0xc2/0x240 [loop] loop_process_work+0x238/0xd00 [loop] process_one_work+0x26b/0x560 worker_thread+0x55/0x3c0 kthread+0x140/0x160 ret_from_fork+0x1f/0x30
-> #1 ((work_completion)(&lo->rootcg_work)){+.+.}-{0:0}: process_one_work+0x245/0x560 worker_thread+0x55/0x3c0 kthread+0x140/0x160 ret_from_fork+0x1f/0x30
-> #0 ((wq_completion)loop0){+.+.}-{0:0}: __lock_acquire+0x10ea/0x1d90 lock_acquire+0xb5/0x2b0 flush_workqueue+0x91/0x5e0 drain_workqueue+0xa0/0x110 destroy_workqueue+0x36/0x250 __loop_clr_fd+0x9a/0x660 [loop] block_ioctl+0x3f/0x50 __x64_sys_ioctl+0x80/0xb0 do_syscall_64+0x38/0x90 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/11595: #0: ffff973ac9812c68 (&lo->lo_mutex){+.+.}-{3:3}, at: __loop_clr_fd+0x41/0x660 [loop]
stack backtrace: CPU: 0 PID: 11595 Comm: losetup Not tainted 5.14.0-rc2+ #407 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014 Call Trace: dump_stack_lvl+0x57/0x72 check_noncircular+0xcf/0xf0 ? stack_trace_save+0x3b/0x50 __lock_acquire+0x10ea/0x1d90 lock_acquire+0xb5/0x2b0 ? flush_workqueue+0x67/0x5e0 ? lockdep_init_map_type+0x47/0x220 flush_workqueue+0x91/0x5e0 ? flush_workqueue+0x67/0x5e0 ? verify_cpu+0xf0/0x100 drain_workqueue+0xa0/0x110 destroy_workqueue+0x36/0x250 __loop_clr_fd+0x9a/0x660 [loop] ? blkdev_ioctl+0x8d/0x2a0 block_ioctl+0x3f/0x50 __x64_sys_ioctl+0x80/0xb0 do_syscall_64+0x38/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7fc21255d4cb
So instead save the bdev and do the put once we've dropped the sb writers lock in order to avoid the lockdep recursion.
Reviewed-by: Anand Jain anand.jain@oracle.com Signed-off-by: Josef Bacik josef@toxicpanda.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/ioctl.c | 15 +++++++++++---- fs/btrfs/volumes.c | 23 +++++++++++++++++------ fs/btrfs/volumes.h | 3 ++- 3 files changed, 30 insertions(+), 11 deletions(-)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 0ba98e08a029..50e12989e84a 100644 --- a/fs/btrfs/ioctl.c +++ b/fs/btrfs/ioctl.c @@ -3205,6 +3205,8 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg) struct inode *inode = file_inode(file); struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); struct btrfs_ioctl_vol_args_v2 *vol_args; + struct block_device *bdev = NULL; + fmode_t mode; int ret; bool cancel = false;
@@ -3237,9 +3239,9 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg) /* Exclusive operation is now claimed */
if (vol_args->flags & BTRFS_DEVICE_SPEC_BY_ID) - ret = btrfs_rm_device(fs_info, NULL, vol_args->devid); + ret = btrfs_rm_device(fs_info, NULL, vol_args->devid, &bdev, &mode); else - ret = btrfs_rm_device(fs_info, vol_args->name, 0); + ret = btrfs_rm_device(fs_info, vol_args->name, 0, &bdev, &mode);
btrfs_exclop_finish(fs_info);
@@ -3255,6 +3257,8 @@ static long btrfs_ioctl_rm_dev_v2(struct file *file, void __user *arg) kfree(vol_args); err_drop: mnt_drop_write_file(file); + if (bdev) + blkdev_put(bdev, mode); return ret; }
@@ -3263,6 +3267,8 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg) struct inode *inode = file_inode(file); struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb); struct btrfs_ioctl_vol_args *vol_args; + struct block_device *bdev = NULL; + fmode_t mode; int ret; bool cancel;
@@ -3284,7 +3290,7 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg) ret = exclop_start_or_cancel_reloc(fs_info, BTRFS_EXCLOP_DEV_REMOVE, cancel); if (ret == 0) { - ret = btrfs_rm_device(fs_info, vol_args->name, 0); + ret = btrfs_rm_device(fs_info, vol_args->name, 0, &bdev, &mode); if (!ret) btrfs_info(fs_info, "disk deleted %s", vol_args->name); btrfs_exclop_finish(fs_info); @@ -3293,7 +3299,8 @@ static long btrfs_ioctl_rm_dev(struct file *file, void __user *arg) kfree(vol_args); out_drop_write: mnt_drop_write_file(file); - + if (bdev) + blkdev_put(bdev, mode); return ret; }
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 8dc14985128f..7f38f81f1a92 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -2119,7 +2119,7 @@ void btrfs_scratch_superblocks(struct btrfs_fs_info *fs_info, }
int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path, - u64 devid) + u64 devid, struct block_device **bdev, fmode_t *mode) { struct btrfs_device *device; struct btrfs_fs_devices *cur_devices; @@ -2233,15 +2233,26 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path, mutex_unlock(&fs_devices->device_list_mutex);
/* - * at this point, the device is zero sized and detached from - * the devices list. All that's left is to zero out the old - * supers and free the device. + * At this point, the device is zero sized and detached from the + * devices list. All that's left is to zero out the old supers and + * free the device. + * + * We cannot call btrfs_close_bdev() here because we're holding the sb + * write lock, and blkdev_put() will pull in the ->open_mutex on the + * block device and it's dependencies. Instead just flush the device + * and let the caller do the final blkdev_put. */ - if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) + if (test_bit(BTRFS_DEV_STATE_WRITEABLE, &device->dev_state)) { btrfs_scratch_superblocks(fs_info, device->bdev, device->name->str); + if (device->bdev) { + sync_blockdev(device->bdev); + invalidate_bdev(device->bdev); + } + }
- btrfs_close_bdev(device); + *bdev = device->bdev; + *mode = device->mode; synchronize_rcu(); btrfs_free_device(device);
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h index 55a8ba244716..f77f869dfd2c 100644 --- a/fs/btrfs/volumes.h +++ b/fs/btrfs/volumes.h @@ -472,7 +472,8 @@ struct btrfs_device *btrfs_alloc_device(struct btrfs_fs_info *fs_info, const u8 *uuid); void btrfs_free_device(struct btrfs_device *device); int btrfs_rm_device(struct btrfs_fs_info *fs_info, - const char *device_path, u64 devid); + const char *device_path, u64 devid, + struct block_device **bdev, fmode_t *mode); void __exit btrfs_cleanup_fs_uuids(void); int btrfs_num_copies(struct btrfs_fs_info *fs_info, u64 logical, u64 len); int btrfs_grow_device(struct btrfs_trans_handle *trans,