btrfs: reinitialize scrub workers

Scrub starts the workers each time a scrub starts and stops them after it
finished. This patch adds an initialization for the workers before each
start, otherwise the workers behave strangely.
Signed-off-by: Arne Jansen <sensille@gmx.net>

fs/btrfs/disk-io.c

@@ -1668,8 +1668,6 @@ struct btrfs_root *open_ctree(struct super_block *sb,
 	init_waitqueue_head(&fs_info->scrub_pause_wait);
 	init_rwsem(&fs_info->scrub_super_lock);
 	fs_info->scrub_workers_refcnt = 0;
-	btrfs_init_workers(&fs_info->scrub_workers, "scrub",
-			   fs_info->thread_pool_size, &fs_info->generic_worker);
 
 	sb->s_blocksize = 4096;
 	sb->s_blocksize_bits = blksize_bits(4096);

fs/btrfs/scrub.c

@@ -1166,8 +1166,12 @@ static noinline_for_stack int scrub_workers_get(struct btrfs_root *root)
 	struct btrfs_fs_info *fs_info = root->fs_info;
 
 	mutex_lock(&fs_info->scrub_lock);
-	if (fs_info->scrub_workers_refcnt == 0)
+	if (fs_info->scrub_workers_refcnt == 0) {
+		btrfs_init_workers(&fs_info->scrub_workers, "scrub",
+			   fs_info->thread_pool_size, &fs_info->generic_worker);
+		fs_info->scrub_workers.idle_thresh = 4;
 		btrfs_start_workers(&fs_info->scrub_workers, 1);
+	}
 	++fs_info->scrub_workers_refcnt;
 	mutex_unlock(&fs_info->scrub_lock);