btrfs: lift uuid_mutex to callers of btrfs_scan_one_device

Prepartory work to fix race between mount and device scan.

The callers will have to manage the critical section, eg. mount wants to
scan and then call btrfs_open_devices without the ioctl scan walking in
and modifying the fs devices in the meantime.

Signed-off-by: David Sterba <dsterba@suse.com>
Reviewed-by: Anand Jain <anand.jain@oracle.com>

fs/btrfs/super.c

@@ -915,8 +915,10 @@ static int btrfs_parse_early_options(const char *options, fmode_t flags,
  error = -ENOMEM;
  goto out;
  }
+ mutex_lock(&uuid_mutex);
  error = btrfs_scan_one_device(device_name,
  flags, holder, fs_devices);
+ mutex_unlock(&uuid_mutex);
  kfree(device_name);
  if (error)
  goto out;
@@ -1537,7 +1539,9 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
  return ERR_PTR(error);
  }
 
+ mutex_lock(&uuid_mutex);
  error = btrfs_scan_one_device(device_name, mode, fs_type, &fs_devices);
+ mutex_unlock(&uuid_mutex);
  if (error)
  goto error_sec_opts;
 
@@ -2232,15 +2236,21 @@ static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
 
  switch (cmd) {
  case BTRFS_IOC_SCAN_DEV:
+ mutex_lock(&uuid_mutex);
  ret = btrfs_scan_one_device(vol->name, FMODE_READ,
  &btrfs_root_fs_type, &fs_devices);
+ mutex_unlock(&uuid_mutex);
  break;
  case BTRFS_IOC_DEVICES_READY:
+ mutex_lock(&uuid_mutex);
  ret = btrfs_scan_one_device(vol->name, FMODE_READ,
  &btrfs_root_fs_type, &fs_devices);
- if (ret)
+ if (ret) {
+ mutex_unlock(&uuid_mutex);
  break;
+ }
  ret = !(fs_devices->num_devices == fs_devices->total_devices);
+ mutex_unlock(&uuid_mutex);
  break;
  case BTRFS_IOC_GET_SUPPORTED_FEATURES:
  ret = btrfs_ioctl_get_supported_features((void __user*)arg);

fs/btrfs/volumes.c

@@ -1226,6 +1226,8 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
  int ret = 0;
  u64 bytenr;
 
+ lockdep_assert_held(&uuid_mutex);
+
  /*
  * we would like to check all the supers, but that would make
  * a btrfs mount succeed after a mkfs from a different FS.
@@ -1244,7 +1246,6 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
  goto error_bdev_put;
  }
 
- mutex_lock(&uuid_mutex);
  device = device_list_add(path, disk_super, &new_device_added);
  if (IS_ERR(device)) {
  ret = PTR_ERR(device);
@@ -1253,7 +1254,6 @@ int btrfs_scan_one_device(const char *path, fmode_t flags, void *holder,
  if (new_device_added)
  btrfs_free_stale_devices(path, device);
  }
- mutex_unlock(&uuid_mutex);
 
  btrfs_release_disk_super(page);