Re: [PATCH 3/4] nvme-apple: move blk_mq_update_nr_hw_queues after nvme_unfreeze

[Keith Busch <kbusch@kernel.org>]

On Mon, Feb 09, 2026 at 03:58:32PM +0100, Christoph Hellwig wrote:
> On Mon, Feb 09, 2026 at 04:29:52PM +0800, Yu Kuai wrote:
> > blk_mq_update_nr_hw_queues() freezes and unfreezes queues internally.
> > When the queue is already frozen before this call (from nvme_start_freeze
> > in apple_nvme_disable), the freeze depth becomes 2. The internal unfreeze
> > only decrements it to 1, leaving the queue still frozen when
> > debugfs_create_files() is called.
> > 
> > This triggers WARN_ON_ONCE(q->mq_freeze_depth != 0) in
> > debugfs_create_files() and risks deadlock.
> > 
> > Fix this by moving nvme_unfreeze() before blk_mq_update_nr_hw_queues()
> > so the queue is unfrozen before the call, allowing the internal
> > freeze/unfreeze to work correctly.
> > 
> > Signed-off-by: Yu Kuai <yukuai@fnnas.com>
> > ---
> >  drivers/nvme/host/apple.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/nvme/host/apple.c b/drivers/nvme/host/apple.c
> > index 15b3d07f8ccd..1835753ad91a 100644
> > --- a/drivers/nvme/host/apple.c
> > +++ b/drivers/nvme/host/apple.c
> > @@ -1202,8 +1202,8 @@ static void apple_nvme_reset_work(struct work_struct *work)
> >  
> >  	nvme_unquiesce_io_queues(&anv->ctrl);
> >  	nvme_wait_freeze(&anv->ctrl);
> > -	blk_mq_update_nr_hw_queues(&anv->tagset, 1);
> >  	nvme_unfreeze(&anv->ctrl);
> > +	blk_mq_update_nr_hw_queues(&anv->tagset, 1);
> 
> Looks good on it's own, but it would also good to align the
> apple driver with the PCI one here more.

I'm pretty sure this series would deadlock nvme-pci, as that driver
still leaves the queue frozen when calling blk_mq_update_nr_hw_queues.

We've left it frozen on purpose, though. The idea was to prevent new IO
from entering a hw context that's no longer backed by a hardware
resourse. Unfreezing prior opens that window up again. Maybe it's not a
big deal; I don't often encounter scenarios where the queue count
changes after a reset.