Re: [PATCH V2] nvme-pci: fix race condition between reset and nvme_dev_disable()

[Keith Busch <kbusch@kernel.org>]

On Tue, Oct 15, 2024 at 11:27:24AM -0600, Keith Busch wrote:
> On Tue, Oct 15, 2024 at 01:21:00PM +0200, Maurizio Lombardi wrote:
> > -static void nvme_pci_update_nr_queues(struct nvme_dev *dev)
> > +static bool nvme_pci_update_nr_queues(struct nvme_dev *dev)
> >  {
> >  	if (!dev->ctrl.tagset) {
> >  		nvme_alloc_io_tag_set(&dev->ctrl, &dev->tagset, &nvme_mq_ops,
> >  				nvme_pci_nr_maps(dev), sizeof(struct nvme_iod));
> > -		return;
> > +		return true;
> > +	}
> > +
> > +	/* Give up if we are racing with nvme_dev_disable() */
> > +	if (!mutex_trylock(&dev->shutdown_lock))
> > +		return false;
> > +
> > +	/* Check if nvme_dev_disable() has been executed already */
> > +	if (!dev->online_queues) {
> > +		mutex_unlock(&dev->shutdown_lock);
> > +		return false;
> >  	}
> >  
> >  	blk_mq_update_nr_hw_queues(&dev->tagset, dev->online_queues - 1);
> >  	/* free previously allocated queues that are no longer usable */
> >  	nvme_free_queues(dev, dev->online_queues);
> > +	mutex_unlock(&dev->shutdown_lock);
> 
> I believe mutex_unlock needs to be above blk_mq_update_nr_hw_queues().
> That function needs all the queues to be frozen, so any older IO that
> times out is going to need this lock in order to reclaim it.

Oops, unlocking there doesn't solve your problem. I guess your patch
should be safe as-is since the nvme driver already waits for the freeze
prior to updating the hw queues.