---

yaml
---
r: 360412
b: refs/heads/master
c: c018dae
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 8c6a3ee6dbd564d05019d396ecb5dc5b35cbc273
+refs/heads/master: c018daecead7a46a575e2a1397fea850b83396c8

trunk/fs/btrfs/ctree.h

@@ -1304,6 +1304,16 @@ struct btrfs_fs_info {
 	 * so it is also safe.
 	 */
 	u64 max_inline;
+	/*
+	 * Protected by ->chunk_mutex and sb->s_umount.
+	 *
+	 * The reason that we use two lock to protect it is because only
+	 * remount and mount operations can change it and these two operations
+	 * are under sb->s_umount, but the read side (chunk allocation) can not
+	 * acquire sb->s_umount or the deadlock would happen. So we use two
+	 * locks to protect it. On the write side, we must acquire two locks,
+	 * and on the read side, we just need acquire one of them.
+	 */
 	u64 alloc_start;
 	struct btrfs_transaction *running_transaction;
 	wait_queue_head_t transaction_throttle;

trunk/fs/btrfs/super.c

@@ -519,7 +519,9 @@ int btrfs_parse_options(struct btrfs_root *root, char *options)
 		case Opt_alloc_start:
 			num = match_strdup(&args[0]);
 			if (num) {
+				mutex_lock(&info->chunk_mutex);
 				info->alloc_start = memparse(num, NULL);
+				mutex_unlock(&info->chunk_mutex);
 				kfree(num);
 				printk(KERN_INFO
 					"btrfs: allocations start at %llu\n",
@@ -1289,7 +1291,9 @@ static int btrfs_remount(struct super_block *sb, int *flags, char *data)
 	fs_info->mount_opt = old_opts;
 	fs_info->compress_type = old_compress_type;
 	fs_info->max_inline = old_max_inline;
+	mutex_lock(&fs_info->chunk_mutex);
 	fs_info->alloc_start = old_alloc_start;
+	mutex_unlock(&fs_info->chunk_mutex);
 	btrfs_resize_thread_pool(fs_info,
 		old_thread_pool_size, fs_info->thread_pool_size);
 	fs_info->metadata_ratio = old_metadata_ratio;