[PATCH] Fix jbd assert failure on IO error.

From: Stephen Tweedie <sct@redhat.com>

The buffer_uptodate flag gets cleared on IO failure, and this can panic jbd
when it tries to write such a buffer.  Relax the panic to be just a warning.

fs/jbd/transaction.c

@@ -666,7 +666,8 @@ do_get_write_access(handle_t *handle, struct journal_head *jh, int force_copy)
 		int offset;
 		char *source;
 
-		J_ASSERT_JH(jh, buffer_uptodate(jh2bh(jh)));
+		J_EXPECT_JH(jh, buffer_uptodate(jh2bh(jh)),
+			    "Possible IO failure.\n");
 		page = jh2bh(jh)->b_page;
 		offset = ((unsigned long) jh2bh(jh)->b_data) & ~PAGE_MASK;
 		source = kmap(page);