Re: [RFC PATCH] scsi: virtio_scsi: bound EH timer resets to avoid unkillable hang

[Nguyen Ngoc Thang]

On 9/14/26 11:17 AM, Hannes Reinecke wrote:
> So the better fix would be to implement a host_reset() callback for
> virtio-scsi which would reset the virtio setup, terminating all
> outstanding commands and reset the queues.

Thanks for the suggestion, Hannes -- that's exactly what the patch
below does (also posted separately as [PATCH v2], Message-ID
<20260914133144.15509-1-ngocthang2710.1999@xxxxxxxxx>; linking it back
into this thread since the subject changed and a couple of mail
clients won't merge the two threads on their own).

It adds eh_host_reset_handler backed by virtio_reset_device(): once
virtio_reset_device() returns, the device is guaranteed to have
stopped touching guest memory, so it's safe to let
scsi_eh_offline_sdevs() free the stuck commands' DMA buffers
afterwards -- the guarantee that was missing before (falling through
to offline with neither target, bus, nor host reset implemented).
Reuses virtscsi_remove_vqs() + virtscsi_init(), the same
teardown/rebuild sequence already used across suspend/resume.

Verified against the same QEMU virtio-scsi repro (PCI_COMMAND_MASTER
cleared mid-write): EH now runs abort -> device reset -> host reset ->
abort -> device reset -> host reset -> offline, dd's stuck fsync
returns EIO, D-state drains to 0, ~244s total.

Suggested-by: Hannes Reinecke <hare@xxxxxxx>
Signed-off-by: Nguyen Ngoc Thang <ngocthang2710.1999@xxxxxxxxx>
---
 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
+ * reset also times out. A virtio reset guarantees the device won't
+ * touch guest memory again, so stuck commands can be freed safely.
+ * Same teardown/rebuild already used for suspend/resume.
+ */
+static int virtscsi_host_reset(struct scsi_cmnd *sc)
+{
+	struct virtio_scsi *vscsi = shost_priv(sc->device->host);
+	struct virtio_device *vdev = vscsi->vdev;
+
+	scmd_printk(KERN_INFO, sc, "host reset\n");
+
+	virtscsi_remove_vqs(vdev);
+	if (virtscsi_init(vdev, vscsi))
+		return FAILED;
+
+	virtio_device_ready(vdev);
+	return SUCCESS;
+}
+
 static int virtscsi_probe(struct virtio_device *vdev)
 {
 	struct Scsi_Host *shost;
-- 
2.43.0

Thanks,
Thang