Re: [PATCH v2] vfio/ccw: Flush notoper_work before returning from reset

[Jason Gunthorpe <jgg@ziepe.ca>]

On Mon, Nov 09, 2026 at 01:38:44PM +0100, Christian Borntraeger wrote:
> Am 06.11.26 um 20:10 schrieb Yuho Choi:
> > vfio_ccw_dma_unmap() is the DMA invalidation callback, which must unpin
> > the pages covering the range before it returns.  It calls
> > vfio_ccw_mdev_reset(), which raises a CLOSE event.
> > 
> > On the normal path fsm_close() calls cp_free() itself, so the pages are
> > unpinned synchronously.  But if the subchannel cannot be disabled or
> > quiesced, fsm_close() falls through to a NOT_OPER event.  Since commit
> > 0c11f61a876e ("s390/vfio_ccw: Move cp cleanup out of not operational"),
> > fsm_notoper() only queues notoper_work, which is where cp_free() then
> > runs.  That commit flushes the work in vfio_ccw_mdev_close_device() and
> > vfio_ccw_mdev_release_dev(), but nothing waits for it on the reset
> > path, so the callback returns with the pages still pinned.
> > 
> > Because notoper_work runs asynchronously, vfio_dma_do_unmap() can exhaust
> > its 10 retries before cp_free() completes, hitting BUG_ON(++retries > 10)
> > and taking the host down.  A further CLOSE cannot help either, as both
> > CLOSE and OPEN are fsm_nop in the NOT_OPER state.
> 
> Does the the iommufd backend have the same problem?
> iopt_unmap_iova_range() keeps calling the unmap callback and gives up with
> WARN_ON(tries > 100) and -EDEADLOCK. So that path is also fixed, I
> guess.

Drivers are not allowed to refuse the shootdown, it is broken if
someone has done this.

Jason