ext4: replace open coded nofail allocation in ext4_free_blocks()

commit 7444a072 upstream.

ext4_free_blocks is looping around the allocation request and mimics
__GFP_NOFAIL behavior without any allocation fallback strategy. Let's
remove the open coded loop and replace it with __GFP_NOFAIL. Without the
flag the allocator has no way to find out never-fail requirement and
cannot help in any way.
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
[bwh: Backported to 3.2:
 - Adjust context
 - s/ext4_free_data_cachep/ext4_free_ext_cachep/]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

fs/ext4/mballoc.c

@@ -4720,18 +4720,12 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 		/*
 		 * blocks being freed are metadata. these blocks shouldn't
 		 * be used until this transaction is committed
+		 *
+		 * We use __GFP_NOFAIL because ext4_free_blocks() is not allowed
+		 * to fail.
 		 */
-	retry:
-		new_entry = kmem_cache_alloc(ext4_free_ext_cachep, GFP_NOFS);
-		if (!new_entry) {
-			/*
-			 * We use a retry loop because
-			 * ext4_free_blocks() is not allowed to fail.
-			 */
-			cond_resched();
-			congestion_wait(BLK_RW_ASYNC, HZ/50);
-			goto retry;
-		}
+		new_entry = kmem_cache_alloc(ext4_free_ext_cachep,
+				GFP_NOFS|__GFP_NOFAIL);
 		new_entry->start_cluster = bit;
 		new_entry->group  = block_group;
 		new_entry->count = count_clusters;