Re: [PATCH v5 05/10] blk-mq: Unregister debugfs attributes earlier

Jens Axboe
2017-04-25T21:41:46Z

On 04/25/2017 02:30 PM, Omar Sandoval wrote:
> On Tue, Apr 25, 2017 at 01:37:40PM -0700, Bart Van Assche wrote:
>> One of the debugfs attributes allows to run a queue. Since running
>> a queue after a queue has entered the "dead" state is not allowed
>> and triggers a use-after-free, unregister the debugfs attributes
>> before a queue reaches the "dead" state.
>
> Still not happy with this commit message. I'd prefer:
>
> We currently call blk_mq_free_queue() from blk_cleanup_queue() before we
> unregister the debugfs attributes for that queue in blk_release_queue().
> This leaves a window open during which accessing most of the mq debugfs
> attributes would cause a use-after-free. Additionally, the "state"
> attribute allows running the queue, which we should not do after the
> queue has entered the "dead" state. Fix both of these cases by
> unregistering the debugfs attributes before this.
>
> Jens, could you ack that dropping the lock is okay?

Looks fine to me. However, I think there's room for improvement here.
Why don't we just make it:

if (!q->mq_ops) {
spin_lock_irq(lock);
__blk_drain_queue(q, true);
} else {
blk_mq_debugfs_unregister_mq(q);
spin_lock_irq(lock);
}

queue_flag_set(QUEUE_FLAG_DEAD, q);
[...]

Would seem much more readable to me, and less dropping/acquiring for
cases where we don't need it.

--
Jens Axboe