Btrfs: do not do fast caching if we are allocating blocks for tree_root

Since the fast caching uses normal tree locking, we can possibly deadlock if we
get to the caching via a btrfs_search_slot() on the tree_root.  So just check to
see if the root we are on is the tree root, and just don't do the fast caching.

Reported-by: Sage Weil <sage@newdream.net>
Signed-off-by: Josef Bacik <josef@redhat.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 8c56f5b389489207760dc027f6a1d8ee8721f9d9..cec05e10014281886014b1274ffe7e4e1e86a6bd 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -429,6 +429,7 @@ err:
 
 static int cache_block_group(struct btrfs_block_group_cache *cache,
                             struct btrfs_trans_handle *trans,
+                            struct btrfs_root *root,
                             int load_cache_only)
 {
        struct btrfs_fs_info *fs_info = cache->fs_info;
@@ -442,9 +443,12 @@ static int cache_block_group(struct btrfs_block_group_cache *cache,
 
        /*
         * We can't do the read from on-disk cache during a commit since we need
-        * to have the normal tree locking.
+        * to have the normal tree locking.  Also if we are currently trying to
+        * allocate blocks for the tree root we can't do the fast caching since
+        * we likely hold important locks.
         */
-       if (!trans->transaction->in_commit) {
+       if (!trans->transaction->in_commit &&
+           (root && root != root->fs_info->tree_root)) {
                spin_lock(&cache->lock);
                if (cache->cached != BTRFS_CACHE_NO) {
                        spin_unlock(&cache->lock);
@@ -4083,7 +4087,7 @@ static int update_block_group(struct btrfs_trans_handle *trans,
                 * space back to the block group, otherwise we will leak space.
                 */
                if (!alloc && cache->cached == BTRFS_CACHE_NO)
-                       cache_block_group(cache, trans, 1);
+                       cache_block_group(cache, trans, NULL, 1);
 
                byte_in_group = bytenr - cache->key.objectid;
                WARN_ON(byte_in_group > cache->key.offset);
@@ -4937,7 +4941,8 @@ have_block_group:
                if (unlikely(block_group->cached == BTRFS_CACHE_NO)) {
                        u64 free_percent;
 
-                       ret = cache_block_group(block_group, trans, 1);
+                       ret = cache_block_group(block_group, trans,
+                                               orig_root, 1);
                        if (block_group->cached == BTRFS_CACHE_FINISHED)
                                goto have_block_group;
 
@@ -4961,7 +4966,8 @@ have_block_group:
                        if (loop > LOOP_CACHING_NOWAIT ||
                            (loop > LOOP_FIND_IDEAL &&
                             atomic_read(&space_info->caching_threads) < 2)) {
-                               ret = cache_block_group(block_group, trans, 0);
+                               ret = cache_block_group(block_group, trans,
+                                                       orig_root, 0);
                                BUG_ON(ret);
                        }
                        found_uncached_bg = true;
@@ -5518,7 +5524,7 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
        u64 num_bytes = ins->offset;
 
        block_group = btrfs_lookup_block_group(root->fs_info, ins->objectid);
-       cache_block_group(block_group, trans, 0);
+       cache_block_group(block_group, trans, NULL, 0);
        caching_ctl = get_caching_control(block_group);
 
        if (!caching_ctl) {