Commit f4cfa9bd authored Jul 22, 2020 by Nikolay Borisov Committed by David Sterba Oct 07, 2020

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>

parent d16c702f

fs/btrfs/volumes.c

+4 −5

Original line number	Diff line number	Diff line
		@@ -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)) {