Commit 849eae5e authored by Anand Jain's avatar Anand Jain Committed by David Sterba
Browse files

btrfs: consolidate device_list_mutex in prepare_sprout to its parent 



btrfs_prepare_sprout() splices seed devices into its own struct fs_devices,
so that its parent function btrfs_init_new_device() can add the new sprout
device to fs_info->fs_devices.

Both btrfs_prepare_sprout() and btrfs_init_new_device() need
device_list_mutex. But they are holding it separately, thus create a
small race window. Close it and hold device_list_mutex across both
functions btrfs_init_new_device() and btrfs_prepare_sprout().

Split btrfs_prepare_sprout() into btrfs_init_sprout() and
btrfs_setup_sprout(). This split is essential because device_list_mutex
must not be held for allocations in btrfs_init_sprout() but must be held
for btrfs_setup_sprout(). So now a common device_list_mutex can be used
between btrfs_init_new_device() and btrfs_setup_sprout().

Reviewed-by: default avatarJosef Bacik <josef@toxicpanda.com>
Signed-off-by: default avatarAnand Jain <anand.jain@oracle.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent fd880809

fs/btrfs/volumes.c

+51 −18
Original line number Diff line number Diff line
@@ -2431,21 +2431,15 @@ struct btrfs_device *btrfs_find_device_by_devspec( 
	return device;

}



/*

 * does all the dirty work required for changing file system's UUID.

 */

static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)

static struct btrfs_fs_devices *btrfs_init_sprout(struct btrfs_fs_info *fs_info)

{

	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;

	struct btrfs_fs_devices *old_devices;

	struct btrfs_fs_devices *seed_devices;

	struct btrfs_super_block *disk_super = fs_info->super_copy;

	struct btrfs_device *device;

	u64 super_flags;



	lockdep_assert_held(&uuid_mutex);

	if (!fs_devices->seeding)

		return -EINVAL;

		return ERR_PTR(-EINVAL);



	/*

	 * Private copy of the seed devices, anchored at
@@ -2453,7 +2447,7 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) 
	 */

	seed_devices = alloc_fs_devices(NULL, NULL);

	if (IS_ERR(seed_devices))

		return PTR_ERR(seed_devices);

		return seed_devices;



	/*

	 * It's necessary to retain a copy of the original seed fs_devices in
@@ -2464,7 +2458,7 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) 
	old_devices = clone_fs_devices(fs_devices);

	if (IS_ERR(old_devices)) {

		kfree(seed_devices);

		return PTR_ERR(old_devices);

		return old_devices;

	}



	list_add(&old_devices->fs_list, &fs_uuids);
@@ -2475,7 +2469,41 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) 
	INIT_LIST_HEAD(&seed_devices->alloc_list);

	mutex_init(&seed_devices->device_list_mutex);



	mutex_lock(&fs_devices->device_list_mutex);

	return seed_devices;

}



/*

 * Splice seed devices into the sprout fs_devices.

 * Generate a new fsid for the sprouted read-write filesystem.

 */

static void btrfs_setup_sprout(struct btrfs_fs_info *fs_info,

			       struct btrfs_fs_devices *seed_devices)

{

	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;

	struct btrfs_super_block *disk_super = fs_info->super_copy;

	struct btrfs_device *device;

	u64 super_flags;



	/*

	 * We are updating the fsid, the thread leading to device_list_add()

	 * could race, so uuid_mutex is needed.

	 */

	lockdep_assert_held(&uuid_mutex);



	/*

	 * The threads listed below may traverse dev_list but can do that without

	 * device_list_mutex:

	 * - All device ops and balance - as we are in btrfs_exclop_start.

	 * - Various dev_list readers - are using RCU.

	 * - btrfs_ioctl_fitrim() - is using RCU.

	 *

	 * For-read threads as below are using device_list_mutex:

	 * - Readonly scrub btrfs_scrub_dev()

	 * - Readonly scrub btrfs_scrub_progress()

	 * - btrfs_get_dev_stats()

	 */

	lockdep_assert_held(&fs_devices->device_list_mutex);



	list_splice_init_rcu(&fs_devices->devices, &seed_devices->devices,

			      synchronize_rcu);

	list_for_each_entry(device, &seed_devices->devices, dev_list)
@@ -2491,13 +2519,10 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info) 
	generate_random_uuid(fs_devices->fsid);

	memcpy(fs_devices->metadata_uuid, fs_devices->fsid, BTRFS_FSID_SIZE);

	memcpy(disk_super->fsid, fs_devices->fsid, BTRFS_FSID_SIZE);

	mutex_unlock(&fs_devices->device_list_mutex);



	super_flags = btrfs_super_flags(disk_super) &

		      ~BTRFS_SUPER_FLAG_SEEDING;

	btrfs_set_super_flags(disk_super, super_flags);



	return 0;

}



/*
@@ -2588,6 +2613,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path 
	struct super_block *sb = fs_info->sb;

	struct rcu_string *name;

	struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;

	struct btrfs_fs_devices *seed_devices;

	u64 orig_super_total_bytes;

	u64 orig_super_num_devices;

	int ret = 0;
@@ -2671,18 +2697,25 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path 


	if (seeding_dev) {

		btrfs_clear_sb_rdonly(sb);

		ret = btrfs_prepare_sprout(fs_info);

		if (ret) {



		/* GFP_KERNEL allocation must not be under device_list_mutex */

		seed_devices = btrfs_init_sprout(fs_info);

		if (IS_ERR(seed_devices)) {

			ret = PTR_ERR(seed_devices);

			btrfs_abort_transaction(trans, ret);

			goto error_trans;

		}

	}



	mutex_lock(&fs_devices->device_list_mutex);

	if (seeding_dev) {

		btrfs_setup_sprout(fs_info, seed_devices);

		btrfs_assign_next_active_device(fs_info->fs_devices->latest_dev,

						device);

	}



	device->fs_devices = fs_devices;



	mutex_lock(&fs_devices->device_list_mutex);

	mutex_lock(&fs_info->chunk_mutex);

	list_add_rcu(&device->dev_list, &fs_devices->devices);

	list_add(&device->dev_alloc_list, &fs_devices->alloc_list);
@@ -2744,7 +2777,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path 


		/*

		 * fs_devices now represents the newly sprouted filesystem and

		 * its fsid has been changed by btrfs_prepare_sprout

		 * its fsid has been changed by btrfs_sprout_splice().

		 */

		btrfs_sysfs_update_sprout_fsid(fs_devices);

	}