On Thu, Jun 25, 2009 at 01:18:59PM -0700, David Rientjes wrote:
> Isn't there also a problem in jbd2_journal_write_metadata_buffer(),
> though?
>
> tmp = jbd2_alloc(bh_in->b_size, GFP_NOFS);
...
> memcpy(tmp, mapped_data + new_offset, jh2bh(jh_in)->b_size);
>
> jbd2_alloc() is just a wrapper to __get_free_pages() and if it fails, it
> appears as though the memcpy() would cause a NULL pointer.
Nicely spotted. Yeah, that's a bug; we need to do something about
that one, too. And what we're doing is a bit silly; it may make sense
to use __get_free_pages if filesystem blocksize == PAGE_SIZE, but
otherwise we should be using a sub-page allocator. Right now, we're
chewing up a 16k PPC page for every 4k filesystem metadata page
allocated in journal_write_metadata_buffer(), and on x86, for the
(admittedly uncommon) 1k block filesystem, we'd be chewing up a 4k
page for a 1k block buffer.
Both of these problems exist for both ext3 and ext4.
- Ted
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