[PATCH 1/4] blk-mq: add API of blk_mq_unfreeze_queue_force

[Christoph Hellwig]

On Fri, Jun 16, 2023 at 03:20:38PM +0800, Ming Lei wrote:
> > > > Shouldn't those writebacks be unblocked by the existing check in
> > > > bio_queue_enter, test_bit(GD_DEAD, &disk->state))? Or are we missing a
> > > > disk state update or wakeup on this condition?
> > > 
> > > GD_DEAD is only set if the device is really dead, then all pending IO
> > > will be failed.
> > 
> > del_gendisk also sets GD_DEAD early on.
> 
> No.
> 
> The hang happens in fsync_bdev() of del_gendisk(), and there are IOs pending on
> bio_queue_enter().

What is the workload here?  If del_gendisk is called to remove a disk
that is in perfectly fine state and can do I/O, fsync_bdev should write
back data, which is what is exists for.  If the disk is dead, we should
have called blk_mark_disk_dead before.