linux-ext4 - Confused by journaling code in ext3_new

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Date:	Wed, 23 Jan 2008 04:07:49 -0500
From:	"Abhishek Rai" <abhishekrai@...gle.com>
To:	linux-ext4@...r.kernel.org
Subject: Confused by journaling code in ext3_new_blocks()

Hi,

I have the following question related to the journaling code in
ext3_new_blocks() function of fs/ext3/balloc.c, any help in this
regard will be greatly appreciated. The code snippet below is taken
from 2.6.24-rc8-mm1 but this code has changed little for a long time
so it's likely that any other recent kernel will also have very
similar code.

ext3_new_blocks()
-> ext3_try_to_allocate_with_rsv()
    -> ext3_journal_dirty_metadata(handle, bitmap_bh)
...
allocated:
if ( /*sanity checking of newly allocated block numbers*/) {
    ext3_error(...);
    goto out;
}

out:
    ...
    brelse(bitmap_bh);
    return 0;

In the above code snippet, ext3_try_to_allocate_with_rsv() is marking
bitmap_bh as dirty metadata _before_ the sanity checks. I'm not
worried about the sanity checks as such, but it seems to me that if
the checks were to fail, we'd be committing the bitmap_bh updates to
disk even though it violates metadata sanity, or am I missing
something here ?

Thanks,
Abhishek
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