Re: IDE locking problem

[Jens Axboe <axboe@suse.de>]

On Sun, Aug 03 2003, Benjamin Herrenschmidt wrote:
> 
> > > would help making sure we don't get a request sneaking in ?
> > 
> > Hmm not really, there's still a chance that could happen.
> 
> Not too familiar with BIO here, but we would need some kind of
> "dead" flag to cause a reject of any try to insert a new request
> in the queue, don't you think ?

That's exactly right.

> Then, IDE could do something like:
> 
>  - set dead flag
>  - wait for all pending requests to drain (easy: insert a barrier
>    in the queue and wait on it, with a hack for the barrier insertion
>    to bypass the dead flag... ugh... maybe a blk_terminate_queue()
>    doing all that would be helpful ?)
>  - unregister blkdev
>  - then tear down the queue (leaving the "empty" queue with the dead
>    flag set, not just memset(...,0,...), so that any bozo keeping a
>    reference to it will be rejected trying to insert request instead
>    of trying to tap an uninitalized queue object
> 
> What do you think ?

Sounds like just the ticket. It's basically impossible to properly
shutdown a queue without being able to quisce it like you describe. IO
events are unpredictable :)

-- 
Jens Axboe