The last step of virtscsi_handle_event is to call virtscsi_kick_event,
which calls INIT_WORK on it's own work item. INIT_WORK resets the
work item's data bits to 0.

If this occurs while the work item is being flushed by
cancel_work_sync, then kernel/workqueue.c/work_offqd_enable triggers a
kernel warning, as it expects the "disable" bit to be 1:

[   21.450115] workqueue: work disable count underflowed
[   21.450117] WARNING: CPU: 1 PID: 56 at kernel/workqueue.c:4328 enable_work+0x10a/0x120
...
[   21.450171] Call Trace:
[   21.450173]  [<000003db2e5bdc3e>] enable_work+0x10e/0x120
[   21.450176] ([<000003db2e5bdc3a>] enable_work+0x10a/0x120)
[   21.450178]  [<000003db2e5bdd86>] cancel_work_sync+0x86/0xa0
[   21.450181]  [<000003daae97d9e4>] virtscsi_remove+0xb4/0xd0 [virtio_scsi]
[   21.450184]  [<000003db2ef3b5ca>] virtio_dev_remove+0x6a/0xd0
[   21.450186]  [<000003db2ef9106c>] device_release_driver_internal+0x1ac/0x260
[   21.450190]  [<000003db2ef8edc8>] bus_remove_device+0xf8/0x190
[   21.450192]  [<000003db2ef88d72>] device_del+0x142/0x340
[   21.450194]  [<000003db2ef88fa0>] device_unregister+0x30/0xa0
[   21.450196]  [<000003db2ef3b2fa>] unregister_virtio_device+0x2a/0x40

This warning may occur if a controller is detached immediately
following a disk detach.

Move the INIT_WORK call to prevent this. Don't re-init event list
work items in virtscsi_kick_event, init them only once in
virtscsi_probe instead.

Signed-off-by: Joshua Daley <jdaley@linux.ibm.com>
---
 drivers/scsi/virtio_scsi.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index 0ed8558dad72..64b6c942f572 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -233,7 +233,6 @@ static void virtscsi_ctrl_done(struct virtqueue *vq)
 	virtscsi_vq_done(vscsi, &vscsi->ctrl_vq, virtscsi_complete_free);
 };
 
-static void virtscsi_handle_event(struct work_struct *work);
 
 static int virtscsi_kick_event(struct virtio_scsi *vscsi,
 			       struct virtio_scsi_event_node *event_node)
@@ -242,7 +241,6 @@ static int virtscsi_kick_event(struct virtio_scsi *vscsi,
 	struct scatterlist sg;
 	unsigned long flags;
 
-	INIT_WORK(&event_node->work, virtscsi_handle_event);
 	sg_init_one(&sg, event_node->event, sizeof(struct virtio_scsi_event));
 
 	spin_lock_irqsave(&vscsi->event_vq.vq_lock, flags);
@@ -984,8 +982,11 @@ static int virtscsi_probe(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
-	if (virtio_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG))
+	if (virtio_has_feature(vdev, VIRTIO_SCSI_F_HOTPLUG)) {
+		for (int i = 0; i < VIRTIO_SCSI_EVENT_LEN; i++)
+			INIT_WORK(&vscsi->event_list[i].work, virtscsi_handle_event);
 		virtscsi_kick_event_all(vscsi);
+	}
 
 	scsi_scan_host(shost);
 	return 0;
-- 
2.34.1

On Wed, Mar 25, 2026 at 07:08:56PM +0100, Joshua Daley wrote:
> The last step of virtscsi_handle_event is to call virtscsi_kick_event,
> which calls INIT_WORK on it's own work item. INIT_WORK resets the
> work item's data bits to 0.
> 
> If this occurs while the work item is being flushed by
> cancel_work_sync, then kernel/workqueue.c/work_offqd_enable triggers a
> kernel warning, as it expects the "disable" bit to be 1:
> 
> [   21.450115] workqueue: work disable count underflowed
> [   21.450117] WARNING: CPU: 1 PID: 56 at kernel/workqueue.c:4328 enable_work+0x10a/0x120
> ...
> [   21.450171] Call Trace:
> [   21.450173]  [<000003db2e5bdc3e>] enable_work+0x10e/0x120
> [   21.450176] ([<000003db2e5bdc3a>] enable_work+0x10a/0x120)
> [   21.450178]  [<000003db2e5bdd86>] cancel_work_sync+0x86/0xa0
> [   21.450181]  [<000003daae97d9e4>] virtscsi_remove+0xb4/0xd0 [virtio_scsi]
> [   21.450184]  [<000003db2ef3b5ca>] virtio_dev_remove+0x6a/0xd0
> [   21.450186]  [<000003db2ef9106c>] device_release_driver_internal+0x1ac/0x260
> [   21.450190]  [<000003db2ef8edc8>] bus_remove_device+0xf8/0x190
> [   21.450192]  [<000003db2ef88d72>] device_del+0x142/0x340
> [   21.450194]  [<000003db2ef88fa0>] device_unregister+0x30/0xa0
> [   21.450196]  [<000003db2ef3b2fa>] unregister_virtio_device+0x2a/0x40
> 
> This warning may occur if a controller is detached immediately
> following a disk detach.
> 
> Move the INIT_WORK call to prevent this. Don't re-init event list
> work items in virtscsi_kick_event, init them only once in
> virtscsi_probe instead.
> 
> Signed-off-by: Joshua Daley <jdaley@linux.ibm.com>
> ---
>  drivers/scsi/virtio_scsi.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>