On 11/3/26 7:51 AM, Stefan Hajnoczi wrote: > On Tue, Nov 03, 2026 at 08:27:52AM +0100, Hannes Reinecke wrote: >> On 11/2/26 9:06 PM, Stefan Hajnoczi wrote: >>> On Mon, Sep 14, 2026 at 08:31:44PM +0700, Nguyen Ngoc Thang wrote: >>>> Once virtscsi_eh_timed_out() lets SCSI EH run on an unresponsive host, >>>> abort and device reset both fail the same way (same dead ctrl vq), and >>>> since virtio_scsi implements neither target nor bus reset, EH falls >>>> through to scsi_eh_offline_sdevs(), which frees the stuck commands' DMA >>>> buffers without any guarantee the device has actually stopped touching >>>> them. If bus mastering (or whatever broke the transport) comes back >>>> later, the device can still write into memory the kernel has already >>>> reused. >>>> >>>> Add a real eh_host_reset_handler instead. virtio_reset_device() is the >>>> guarantee scsi_eh_offline_sdevs() was missing: once it returns, the >>>> device will not touch guest memory again, so it is safe to hand >>>> outstanding commands' buffers back. Reuse virtscsi_remove_vqs() + >>>> virtscsi_init() -- the exact sequence already used across >>>> suspend/resume -- to tear the virtqueues down and rebuild them. >>>> >>>> Verified with a QEMU virtio-scsi repro (PCI_COMMAND_MASTER cleared >>>> mid-write): EH now runs abort -> device reset -> host reset -> abort -> >>>> device reset -> host reset -> offline, then dd's stuck fsync returns >>>> EIO and D-state drains to 0, in ~244s total. No task remains >>>> uninterruptibly blocked. >>> By the way, there is a known limitation in the QEMU virtio-scsi >>> implementation where some reset-related operations are implemented >>> synchronously (can block vCPUs and QEMU activity while waiting for I/O >>> to drain in some situations) instead of asynchronously. Recently there >>> has been work in QEMU to make VIRTIO device reset asynchronous, for >>> example, but it needs to be implemented on a per-device basis and >>> virtio-scsi hasn't taken advantage of it yet. >>> >>> Please let me know if you'd like to discuss or contribute. It's >>> something that is on my radar but not until 2027. >>> >>>> Suggested-by: Hannes Reinecke <[email protected]> >>>> Signed-off-by: Nguyen Ngoc Thang <[email protected]> >>>> --- >>>> v1 -> v2: implemented eh_host_reset_handler as suggested by Hannes >>>> Reinecke in review of the original RFC, instead of relying solely on >>>> the EH loop falling through to offline. >>>> --- >>>> drivers/scsi/virtio_scsi.c | 24 ++++++++++++++++++++++++ >>>> 1 file changed, 24 insertions(+) >>>> >>>> diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c >>>> index b4f20c487718..9698f4f91cc6 100644 >>>> --- a/drivers/scsi/virtio_scsi.c >>>> +++ b/drivers/scsi/virtio_scsi.c >>>> @@ -833,6 +833,8 @@ static enum scsi_timeout_action >>>> virtscsi_eh_timed_out(struct scsi_cmnd *scmnd) >>>> return SCSI_EH_NOT_HANDLED; >>>> } >>>> +static int virtscsi_host_reset(struct scsi_cmnd *sc); >>>> + >>>> static const struct scsi_host_template virtscsi_host_template = { >>>> .module = THIS_MODULE, >>>> .name = "Virtio SCSI HBA", >>>> @@ -846,6 +848,7 @@ static const struct scsi_host_template >>>> virtscsi_host_template = { >>>> .eh_abort_handler = virtscsi_abort, >>>> .eh_device_reset_handler = virtscsi_device_reset, >>>> .eh_timed_out = virtscsi_eh_timed_out, >>>> + .eh_host_reset_handler = virtscsi_host_reset, >>>> .sdev_init = virtscsi_device_alloc, >>>> .dma_boundary = UINT_MAX, >>>> @@ -947,6 +950,27 @@ static int virtscsi_init(struct virtio_device *vdev, >>>> return err; >>>> } >>>> +/* >>>> + * No bus/target reset in virtio-scsi, so EH lands here after device >>> The choice to use the VIRTIO device reset in virtscsi_host_reset() looks >>> good to me, but I would like clarification on this comment. virtio-scsi >>> does have I_T_NEXUS_RESET and I believe this is the modern equivalent to >>> the pre-SCSI-6 TARGET RESET. Is it really the case that virtio-scsi >>> doesn't have target reset? And do you want to go ahead and implement >>> .eh_target_reset_handler() using I_T_NEXUS_RESET? >>> >> Would probably not a bad idea to use I_T_NEXUS_RESET here. >> Not sure what it does internally, though; _is_ there a nexus >> to reset? > Whether there is any benefit to I_T_NEXUS_RESET may depend on the device > implementation. In QEMU: > - LOGICAL_UNIT_RESET resets just 1 LUN > - I_T_NEXUS_RESET resets all LUNs > - VIRTIO device reset also resets the HBA itself > > In practice QEMU's I_T_NEXUS_RESET is unlikely to fix things if > LOGICAL_UNIT_RESET wasn't sufficient. Maybe it will help on other device > implementations though. > > I think the Linux driver mapping should be: > - .eh_device_reset_handler() -> LOGICAL_UNIT_RESET > - .eh_target_reset_handler() -> I_T_NEXUS_RESET > - .eh_host_reset_handler() -> VIRTIO device reset
How are vhost drivers notified of the device reset? For qemu virtio-scsi this would call virtio_scsi_reset right? For vhost-scsi though, do we need to add a similar reset function?
