btrfs: use RCU for quick device check in btrfs_init_new_device
When adding a new device there's a mandatory check to see if a device is
being duplicated to the filesystem it's added to. Since this is a
read-only operations not necessary to take device_list_mutex and can simply
make do with an rcu-readlock.
Using just RCU is safe because there won't be another device add delete
running in parallel as btrfs_init_new_device is called only from
btrfs_ioctl_add_dev.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 29c6f01..5449e38 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2515,16 +2515,15 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
filemap_write_and_wait(bdev->bd_inode->i_mapping);
- mutex_lock(&fs_devices->device_list_mutex);
- list_for_each_entry(device, &fs_devices->devices, dev_list) {
+ rcu_read_lock();
+ list_for_each_entry_rcu(device, &fs_devices->devices, dev_list) {
if (device->bdev == bdev) {
ret = -EEXIST;
- mutex_unlock(
- &fs_devices->device_list_mutex);
+ rcu_read_unlock();
goto error;
}
}
- mutex_unlock(&fs_devices->device_list_mutex);
+ rcu_read_unlock();
device = btrfs_alloc_device(fs_info, NULL, NULL);
if (IS_ERR(device)) {
