[PATCH] ext3: handle attempted double-delete of metadata.

This patch improves ext3's ability to deal with corruption on-disk.  If we
try to delete a metadata block twice, we confuse ext3's internal revoke
error-checking, resulting in a BUG().  But this can occur in practice due
to a corrupt indirect block, so we should attempt to fail gracefully.

Downgrade the assert failure to a JH_EXPECT_BH failure, and return EIO when
it occurs.

This is easily reproduced with a sample ext3 fs image containing an inode
which references the same indirect block more than once.  Deleting that
inode will BUG() an unfixed kernel with:

Assertion failure in journal_revoke() at fs/jbd/revoke.c:379:
"!buffer_revoked(bh)"

With the fix, ext3 recovers gracefully.
Signed-off-by: Stephen Tweedie <sct@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/jbd/revoke.c

@@ -376,7 +376,12 @@ int journal_revoke(handle_t *handle, unsigned long blocknr,
            first having the revoke cancelled: it's illegal to free a
            block twice without allocating it in between! */
 	if (bh) {
-		J_ASSERT_BH(bh, !buffer_revoked(bh));
+		if (!J_EXPECT_BH(bh, !buffer_revoked(bh),
+				 "inconsistent data on disk")) {
+			if (!bh_in)
+				brelse(bh);
+			return -EIO;
+		}
 		set_buffer_revoked(bh);
 		set_buffer_revokevalid(bh);
 		if (bh_in) {