[PATCH] jbd2: clear BH_Delay & BH_Unwritten in journal_unmap_buffer

[Eric Sandeen <sandeen@redhat.com>]

journal_unmap_buffer()'s zap_buffer: code clears a lot of buffer head
state ala discard_buffer(), but does not touch _Delay or _Unwritten
as discard_buffer() does.

This can be problematic in some areas of the ext4 code which assume
that if they have found a buffer marked unwritten or delay, then it's
a live one.  Perhaps those spots should check whether it is mapped
as well, but if jbd2 is going to tear down a buffer, let's really
tear it down completely.

Without this I get some fsx failures on sub-page-block filesystems
up until v3.2, at which point 4e96b2dbbf1d7e81f22047a50f862555a6cb87cb
and 189e868fa8fdca702eb9db9d8afc46b5cb9144c9 make the failures go
away, because buried within that large change is some more flag
clearing.  I still think it's worth doing in jbd2, since
->invalidatepage leads here directly, and it's the right place
to clear away these flags.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Cc: stable@vger.kernel.org
---

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 35ae096..52653306 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1949,6 +1949,8 @@ zap_buffer_unlocked:
 	clear_buffer_mapped(bh);
 	clear_buffer_req(bh);
 	clear_buffer_new(bh);
+	clear_buffer_delay(bh);
+	clear_buffer_unwritten(bh);
 	bh->b_bdev = NULL;
 	return may_free;
 }