btrfs: delay blkdev_put until after the device remove

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>

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 41524f9..cc61813 100644 (file)
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3223,6 +3223,8 @@ 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;
 
@@ -3255,9 +3257,9 @@ 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);
 
@@ -3273,6 +3275,8 @@ out:
        kfree(vol_args);
 err_drop:
        mnt_drop_write_file(file);
+       if (bdev)
+               blkdev_put(bdev, mode);
        return ret;
 }
 
@@ -3281,6 +3285,8 @@ 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;
 
@@ -3302,7 +3308,7 @@ 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);
@@ -3311,7 +3317,8 @@ 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 1a9eeb2..97189ae 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2059,7 +2059,7 @@ 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;
@@ -2173,15 +2173,26 @@ 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 b082250..2183361 100644 (file)
--- 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,