Btrfs: Fix deadlock while searching for dead roots on mount

btrfs_find_dead_roots called btrfs_read_fs_root_no_radix, which
means we end up calling btrfs_search_slot with a path already held.

The fix is to remember the key inside btrfs_find_dead_roots and drop
the path.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --git a/fs/btrfs/root-tree.c b/fs/btrfs/root-tree.c
index 8bf21ba..a5c0e98 100644 (file)
--- a/fs/btrfs/root-tree.c
+++ b/fs/btrfs/root-tree.c
@@ -154,6 +154,7 @@ int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid,
        struct btrfs_item *item;
        struct btrfs_root_item *ri;
        struct btrfs_key key;
+       struct btrfs_key found_key;
        struct btrfs_path *path;
        int ret;
        u32 nritems;
@@ -166,6 +167,8 @@ int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid,
        path = btrfs_alloc_path();
        if (!path)
                return -ENOMEM;
+
+again:
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto err;
@@ -196,7 +199,11 @@ int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid,
                if (btrfs_disk_root_refs(leaf, ri) != 0)
                        goto next;
 
-               dead_root = btrfs_read_fs_root_no_radix(root->fs_info, &key);
+               memcpy(&found_key, &key, sizeof(key));
+               key.offset++;
+               btrfs_release_path(root, path);
+               dead_root = btrfs_read_fs_root_no_radix(root->fs_info,
+                                                       &found_key);
                if (IS_ERR(dead_root)) {
                        ret = PTR_ERR(dead_root);
                        goto err;
@@ -206,6 +213,7 @@ int btrfs_find_dead_roots(struct btrfs_root *root, u64 objectid,
                                          &root->fs_info->dead_roots);
                if (ret)
                        goto err;
+               goto again;
 next:
                slot++;
                path->slots[0]++;