Re: IDE locking problem

[Jens Axboe <axboe@suse.de>]

On Sun, Aug 03 2003, Benjamin Herrenschmidt wrote:
> Hi Alan & Bart !
> 
> While fixing my hotswap media-bay IDE controller for 2.6, I found
> a locking problem with IDE (again ? :) in ide_unregister_hw. Basically
> the problem is that it calls blk_cleanup_queue(), which is unsafe to
> call with a lock held (it will call flush_workqueue() at one point).
> Other side effect, flush_workqueue() will re-enable IRQs, thus allowing
> us to get an IRQ while holding the spinlock -> double lock, but that's
> just a side effect of calling flush_workqueue in that context.

Irk someone made blk_cleanup_queue() non-atomic. I blame Andrew. And now
it looks like it's impossible to make it atomic again :/. Not very nice,
imo it's preferable to keep such unregister functions atomic.

> So the call to blk_cleanup_queue() shall be moved outside of the
> spinlock. I don't know much about the BIO details, is it possible
> to first unregister_blkdev, then only call blk_cleanup_queue() ? That

That should work, yes.

> would help making sure we don't get a request sneaking in ?

Hmm not really, there's still a chance that could happen.

-- 
Jens Axboe