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>

1 files changed, 12 insertions, 6 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 8c56f5b38948..cec05e100142 100644
--- 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) {