1 files changed, 19 insertions, 4 deletions

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index 1f5cf5880718..4eec399ec807 100644
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -520,8 +520,8 @@ static void ext4_xattr_update_super_block(handle_t *handle,
 }
 
 /*
- * Release the xattr block BH: If the reference count is > 1, decrement
- * it; otherwise free the block.
+ * Release the xattr block BH: If the reference count is > 1, decrement it;
+ * otherwise free the block.
  */
 static void
 ext4_xattr_release_block(handle_t *handle, struct inode *inode,
@@ -542,16 +542,31 @@ ext4_xattr_release_block(handle_t *handle, struct inode *inode,
                 if (ce)
                         mb_cache_entry_free(ce);
                 get_bh(bh);
+                unlock_buffer(bh);
                 ext4_free_blocks(handle, inode, bh, 0, 1,
                                  EXT4_FREE_BLOCKS_METADATA |
                                  EXT4_FREE_BLOCKS_FORGET);
-                unlock_buffer(bh);
         } else {
                 le32_add_cpu(&BHDR(bh)->h_refcount, -1);
                 if (ce)
                         mb_cache_entry_release(ce);
+                /*
+                 * Beware of this ugliness: Releasing of xattr block references
+                 * from different inodes can race and so we have to protect
+                 * from a race where someone else frees the block (and releases
+                 * its journal_head) before we are done dirtying the buffer. In
+                 * nojournal mode this race is harmless and we actually cannot
+                 * call ext4_handle_dirty_xattr_block() with locked buffer as
+                 * that function can call sync_dirty_buffer() so for that case
+                 * we handle the dirtying after unlocking the buffer.
+                 */
+                if (ext4_handle_valid(handle))
+                        error = ext4_handle_dirty_xattr_block(handle, inode,
+                                                              bh);
                 unlock_buffer(bh);
-                error = ext4_handle_dirty_xattr_block(handle, inode, bh);
+                if (!ext4_handle_valid(handle))
+                        error = ext4_handle_dirty_xattr_block(handle, inode,
+                                                              bh);
                 if (IS_SYNC(inode))
                         ext4_handle_sync(handle);
                 dquot_free_block(inode, EXT4_C2B(EXT4_SB(inode->i_sb), 1));