[PATCH v3 2/3] scsi: virtio_scsi: move INIT_WORK calls to virtscsi_init

[Joshua Daley <jdaley@linux.ibm.com>]

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_init instead.

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Signed-off-by: Joshua Daley <jdaley@linux.ibm.com>
---
 drivers/scsi/virtio_scsi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/virtio_scsi.c b/drivers/scsi/virtio_scsi.c
index 982f49bc6c69..15ca2a2d7aa4 100644
--- a/drivers/scsi/virtio_scsi.c
+++ b/drivers/scsi/virtio_scsi.c
@@ -242,7 +242,6 @@ 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);
@@ -898,6 +897,9 @@ static int virtscsi_init(struct virtio_device *vdev,
 	virtscsi_config_set(vdev, cdb_size, VIRTIO_SCSI_CDB_SIZE);
 	virtscsi_config_set(vdev, sense_size, VIRTIO_SCSI_SENSE_SIZE);
 
+	for (i = 0; i < VIRTIO_SCSI_EVENT_LEN; i++)
+		INIT_WORK(&vscsi->event_list[i].work, virtscsi_handle_event);
+
 	err = 0;
 
 out:
-- 
2.34.1