[PATCH v2] vhost-scsi: serialize completion notification with callfd updates

vhost_scsi_complete_cmd_work() drops the virtqueue mutex before calling
vhost_signal(). VHOST_SET_VRING_CALL replaces call_ctx.ctx and releases the
old eventfd_ctx while holding the same mutex. vhost_signal() reads the call
context before and after vhost_notify(), so a concurrent callfd update can
make it signal a freed context or NULL.

KASAN reported the use through:

	eventfd_signal_mask
	vhost_signal
	vhost_scsi_complete_cmd_work

The context was released through:

	eventfd_ctx_put
	vhost_vring_ioctl
	vhost_scsi_ioctl

Keep the mutex held through vhost_signal() so completion notification and
callfd updates are serialized.

Fixes: 057cbf49a1f0 ("tcm_vhost: Initial merge for vhost level target fabric driver")
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jia Jia <[email protected]>
---
Changes since RFC:
- Send as a non-RFC v2.
- Add Fixes and Link tags.

 drivers/vhost/scsi.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/vhost/scsi.c b/drivers/vhost/scsi.c
index 9a1253b9d8c5..7f46bc0de3c2 100644
--- a/drivers/vhost/scsi.c
+++ b/drivers/vhost/scsi.c
@@ -735,10 +735,9 @@ static void vhost_scsi_complete_cmd_work(struct vhost_work *work)
 		vhost_scsi_release_cmd_res(se_cmd);
 	}
 
-	mutex_unlock(&svq->vq.mutex);
-
 	if (signal)
 		vhost_signal(&svq->vs->dev, &svq->vq);
+	mutex_unlock(&svq->vq.mutex);
 }
 
 static struct vhost_scsi_cmd *
-- 
2.34.1