Commit c5593ca3 authored by David Sterba's avatar David Sterba
Browse files

btrfs: switch to RCU for device traversal in btrfs_ioctl_dev_info 



We don't need to use the mutex as we do not modify the devices nor the
list itself and just read some information:

does not change during device lifetime:
- devid
- uuid
- name (ie. the path)

may change in parallel to the ioctl call, but can lead only to reporting
inacurracy:
- bytes_used
- total_bytes

Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 08ffcae8

fs/btrfs/ioctl.c

+2 −5
Original line number Diff line number Diff line
@@ -2775,7 +2775,6 @@ static long btrfs_ioctl_dev_info(struct btrfs_fs_info *fs_info, 
{

	struct btrfs_ioctl_dev_info_args *di_args;

	struct btrfs_device *dev;

	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;

	int ret = 0;

	char *s_uuid = NULL;
@@ -2786,7 +2785,7 @@ static long btrfs_ioctl_dev_info(struct btrfs_fs_info *fs_info, 
	if (!btrfs_is_empty_uuid(di_args->uuid))

		s_uuid = di_args->uuid;



	mutex_lock(&fs_devices->device_list_mutex);

	rcu_read_lock();

	dev = btrfs_find_device(fs_info, di_args->devid, s_uuid, NULL);



	if (!dev) {
@@ -2801,17 +2800,15 @@ static long btrfs_ioctl_dev_info(struct btrfs_fs_info *fs_info, 
	if (dev->name) {

		struct rcu_string *name;



		rcu_read_lock();

		name = rcu_dereference(dev->name);

		strncpy(di_args->path, name->str, sizeof(di_args->path));

		rcu_read_unlock();

		di_args->path[sizeof(di_args->path) - 1] = 0;

	} else {

		di_args->path[0] = '\0';

	}



out:

	mutex_unlock(&fs_devices->device_list_mutex);

	rcu_read_unlock();

	if (ret == 0 && copy_to_user(arg, di_args, sizeof(*di_args)))

		ret = -EFAULT;

CRA Git | Maintained and supported by SUSTech CRA and CCSE