[PATCH] ext3 truncate fix

Forward-port of a fix which Stephen has applied to ext3's 2.4 CVS tree.

Fix for a rare problem seen under stress in data=journal mode: if we
have to restart a truncate transaction while traversing the inode's
direct blocks, we need to deal with bh==NULL in ext3_clear_blocks.

fs/ext3/inode.c

@@ -1632,9 +1632,11 @@ ext3_clear_blocks(handle_t *handle, struct inode *inode, struct buffer_head *bh,
 		}
 		ext3_mark_inode_dirty(handle, inode);
 		ext3_journal_test_restart(handle, inode);
-		BUFFER_TRACE(bh, "get_write_access");
+		if (bh) {
+			BUFFER_TRACE(bh, "retaking write access");
 			ext3_journal_get_write_access(handle, bh);
 		}
+	}
 
 	/*
 	 * Any buffers which are on the journal will be in memory. We find