On Mon, Apr 24, 2017 at 10:26:15AM -0700, Omar Sandoval wrote: > On Mon, Apr 24, 2017 at 05:24:13PM +0000, Bart Van Assche wrote: > > On Mon, 2017-04-24 at 10:17 -0700, Omar Sandoval wrote: > > > 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: > > > > > > @@ -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? > > > > That would have the disadvantage that debugfs attributes would be > > unregistered > > before __blk_drain_queue() is called and hence that these debugfs attributes > > would not be available to debug hangs in queue draining for traditional > > block > > layer queues ... > > True, this is probably fine, then.
Actually, if we drop this lock, then for non-mq, can't we end up with some I/O's sneaking in between when we drain the queue and mark it dead while the lock is dropped?
