Re: [PATCH v5 05/21] virtio-scsi: stop using aio_disable_external() during unplug

[Stefan Hajnoczi <stefanha@xxxxxxxxxx>]

On Tue, May 09, 2023 at 08:55:14PM +0200, Kevin Wolf wrote:
> Am 04.05.2023 um 21:53 hat Stefan Hajnoczi geschrieben:
> > This patch is part of an effort to remove the aio_disable_external()
> > API because it does not fit in a multi-queue block layer world where
> > many AioContexts may be submitting requests to the same disk.
> > 
> > The SCSI emulation code is already in good shape to stop using
> > aio_disable_external(). It was only used by commit 9c5aad84da1c
> > ("virtio-scsi: fixed virtio_scsi_ctx_check failed when detaching scsi
> > disk") to ensure that virtio_scsi_hotunplug() works while the guest
> > driver is submitting I/O.
> > 
> > Ensure virtio_scsi_hotunplug() is safe as follows:
> > 
> > 1. qdev_simple_device_unplug_cb() -> qdev_unrealize() ->
> >    device_set_realized() calls qatomic_set(&dev->realized, false) so
> >    that future scsi_device_get() calls return NULL because they exclude
> >    SCSIDevices with realized=false.
> > 
> >    That means virtio-scsi will reject new I/O requests to this
> >    SCSIDevice with VIRTIO_SCSI_S_BAD_TARGET even while
> >    virtio_scsi_hotunplug() is still executing. We are protected against
> >    new requests!
> > 
> > 2. scsi_device_unrealize() already contains a call to
> 
> I think you mean scsi_qdev_unrealize(). Can be fixed while applying.

Yes, it should be scsi_qdev_unrealize(). I'll review your other comments
and fix this if I need to respin.

Stefan

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