On Jul 30, 2007, at 2:58 PM, Badari Pulavarty wrote:
On Mon, 2007-07-30 at 14:45 -0700, Zach Brown wrote:
I am also taking a look at it right now.
Are we having a race to write a little test app that reproduces the
problem? :)
Nope. Feel free to write the test case.
Well, I'm having a heck of a time getting this to fail. It looks
possible, though. Joe, were you guys able to narrow it down to a
reproducible test case? Do you have any oops output messages from
the crashes?
It looks like it takes a very particular set of circumstances to
actually crash after relying on an uninitialized map_bh. (see the
blkfactor, buffer_new(), and this_chunk_blocks tests in dio_zero_block
()).
I am just looking at the code
to see what needs to be done.
It looks like the unconditional dio_cleanup() and dio_zero_block()
calls outside the nseg loop are relying on state which might not have
been built up. _zero_block() tests map_bh's flags without them being
set. _cleanup could, in some crazy world, get confused if we managed
to get here with a 0 nr_segs because dio->head and ->tail wouldn't be
initialized.
So we could initialize some more fields at the start of
direct_io_worker for the benefit of these cleanup calls. Or we could
conditionally call them based on some other indicator of progress.
Neither really thrills me.
And I don't have a test case to verify changes with. Meh.
How do you feel about initializing the dio with kzalloc() and only
initializing the fields that we rely on being non-zero, and
commenting the hell out of it?
- z
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