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SubjectRe: bio refcount problem
On Fri, Feb 18 2005, Philip R Auld wrote:
> Hi,
>
> Rumor has it that on Fri, Feb 18, 2005 at 02:59:32PM +0100 Jens Axboe said:
> > On Fri, Feb 18 2005, Philip R Auld wrote:
>
> ...
> > > Or make all users of submit_bio take and release and extra reference
> > > like submit_bh.
> >
> > The queue lock is still held at that point, so the driver hasn't had a
> > chance to process the request yet.
>
> Interesting. This is not a theoretical problem though. I've got traces of
> the oops showing the bio getting freed before the bio_sync(bio) test.
> When you say driver here what level do you mean? scsi_request_fn at
> least drops the queue lock.

But it must be holding the lock to retrieve the request in question, so
there should be no opening for a completion race there.

> What if it's merged instead of added directly? That could also get to
> the same place.

Same deal - if the request is already seen by the driver, merging is not
allowed. If not, then the same rules apply.

> The end_io callback _is_ getting called before __make_request
> does its "if(bio_sync(bio))" test.

Sounds strange, it sounds like a driver issue. If you have time, please
do poke some more at this. I'll try to be responsive, but I'm busy with
other things atm. Are you using a vanilla kernel?

--
Jens Axboe

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