Re: 2.6.18 ext3 panic.

Jan Kara
2006-10-12T12:28:35Z

> Badari Pulavarty wrote:
>
> >Here is what I think is happening..
> >
> >journal_unmap_buffer() - cleaned the buffer, since its outside EOF, but
> >its a part of the same page. So it remained on the page->buffers
> >list. (at this time its not part of any transaction).
> >
> >Then, ordererd_commit_write() called journal_dirty_data() and we added
> >all these buffers to BJ_SyncData list. (at this time buffer is clean -
> >not dirty).
> >
> >Now msync() called __set_page_dirty_buffers() and dirtied *all* the
> >buffers attached to this page.
> >
> >journal_submit_data_buffers() got around to this buffer and tried to
> >submit the buffer...
Yes, this is certainly one we need to fix.

> This seems about right, but one thing bothers me in the traces; it seems
> like there is some locking that is missing. In
> http://people.redhat.com/esandeen/traces/eric_ext3_oops1.txt
> for example, it looks like journal_dirty_data gets started, but then the
> buffer_head is acted on by journal_unmap_buffer, which decides this buffer
> is part of the running transaction, past EOF, and clears mapped, dirty,
It's part of the committing transaction.

> etc. Then journal_dirty_data picks up again, decides that the buffer is
> not on the right list (now BJ_None) and puts it back on BJ_SyncData. Then
> it gets picked up by journal_submit_data_buffers and submitted, and oops.
Now it is put on the running transaction's BJ_SyncData list. But
otherwise you're right.

> Talking with Stephen, it seemed like the page lock should synchronize these
> threads, but I've found that we can get to journal_dirty_data acting on the
> buffer heads w/o having the page locked...
Yes, PageLock should protect us. Where can we call
journal_dirty_data() without PageLock? I see the following callers:
ext3_ordered_commit_write - should have PageLock
ext3_ordered_writepage - has PageLock
ext3_block_truncate_page - has PageLock

And that are all callers from ext3. Am I missing something?

Honza
--
Jan Kara <jack@suse.cz>
SuSE CR Labs