On Mon, Apr 24, 2017 at 05:12:05PM +0000, Bart Van Assche wrote: > On Mon, 2017-04-24 at 09:55 -0700, Omar Sandoval wrote: > > On Fri, Apr 21, 2017 at 04:40:21PM -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 even can cause a kernel crash, unregister the debugfs attributes > > > before a queue reaches the "dead" state. > > > > More important than this case, I think, is that blk_cleanup_queue() > > calls blk_mq_free_queue(q), so most of the debugfs entries would lead to > > use-after-frees. If you add that to the commit message and address my > > comment below, > > > > Reviewed-by: Omar Sandoval <[email protected]> > > Thanks! I will update the commit message. > > > > --- a/block/blk-core.c > > > +++ b/block/blk-core.c > > > @@ -566,6 +566,11 @@ void blk_cleanup_queue(struct request_queue *q) > > > spin_lock_irq(lock); > > > if (!q->mq_ops) > > > __blk_drain_queue(q, true); > > > + spin_unlock_irq(lock); > > > + > > > + blk_mq_debugfs_unregister_mq(q); > > > + > > > + spin_lock_irq(lock); > > > queue_flag_set(QUEUE_FLAG_DEAD, q); > > > spin_unlock_irq(lock); > > > > Do we actually have to hold the queue lock when we set QUEUE_FLAG_DEAD? > > It's way easier to keep that spin_lock()/spin_unlock() pair than to analyze > the block driver core and all block drivers to see whether or not any > concurrent queue flag changes could occur.
Ah, I didn't realize that queue_flag_set() did a non-atomic set. I'm wondering if anything bad could happen if something raced between when we drop the lock and regrab it. Maybe just move the blk_mq_debugfs_unregister_mq() before we grab the lock the first time instead?
