[PATCH 0/5] jbd: possible filesystem corruption fixes (take 2)

Hidehiro Kawai
2008-06-02T10:40:53Z

Subject: [PATCH 0/5] jbd: possible filesystem corruption fixes (take 2)

This patch set is the take 2 of fixing error handling problem in
ext3/JBD. The previous discussion can be found here:
http://lkml.org/lkml/2008/5/14/10

The same problem should also be in ext4/JBD, but I haven't prepared
it yet.

Problem
=======
Currently some error checkings are missing, so the journal cannot abort
correctly. This causes breakage of the ordered mode rule and filesystem
corruption. Missing error checkings are:

(1) error check for dirty buffers flushed before the commit
(addressed by PATCH 1/5 and 2/5)
(2) error check for the metadata writes to the journal before the
commit (addressed by PATCH 3/5)
(3) error check for checkpointing and replay (addressed by PATCH 4/5
and 5/5)

Changes from take 1
===================
[PATCH 1/5]
o not changed

[PATCH 2/5]
o rewrite my coment in journal_dirty_data() comprehensibly

[PATCH 3/5]
o check for errors and abort the journal just before
journal_write_commit_record() instead of after writing metadata
buffers

[PATCH 4/5 and 5/5]
o separate the ext3 part from the jbd part in a patch
o use JFS_ABORT for checkpointing failures instead of introducing
JFS_CP_ABORT flag
o don't update only the journal super block, but also j_tail and
j_tail_sequence when the journal has aborted (at least we only
have to avoid updating the super block, but keeping j_tail*'s
values will be good thing because it may protect someone from
adding bugs in the future)
o journal_destroy() returns -EIO when the journal has aborted so that
ext3_put_super() can detect the abort
o journal_flush() uses j_checkpoint_mutex to avoid a race with
__log_wait_for_space()

The last item targets a newly found problem. journal_flush() can be
called while processing __log_wait_for_space(). In this case,
cleanup_journal_tail() can be called between
__journal_drop_transaction() and journal_abort(), then
the transaction with checkpointing failure is lost from the journal.
Using j_checkpoint_mutex which is used by __log_wait_for_space(),
we should avoid the race condition. But the test is not so sufficient
because it is very difficult to produce this race. So I hope that
this locking is reviewed carefully (including a possibility of
deadlock.)

Regards,

--
Hidehiro Kawai
Hitachi, Systems Development Laboratory
Linux Technology Center