[PATCH] virtio_ring: tag event_triggered as racy for KCSAN

[Michael S. Tsirkin]

event_triggered is fundamentally racy. There are races of 2 types:
1. vq processing can read false value while interrupt
   triggered and set it to true.
   result will be a bit of extra work when disabling cbs, no big deal.

1. vq processing can set false value then interrupt
   immediately sets true value
   since interrupt then triggers a callback which will
   process buffers, this is also not an issue.

However, looks like KCSAN isn't smart enough to figure this out.
Tag the field __data_racy for now.
We should probably look at ways to make this more straight-forwardly
correct.

Cc: Marco Elver <elver@xxxxxxxxxx>
Reported-by: syzbot+8a02104389c2e0ef5049@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index be7309b1e860..724aa9c27c6b 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -194,7 +194,7 @@ struct vring_virtqueue {
 	u16 last_used_idx;
 
 	/* Hint for event idx: already triggered no need to disable. */
-	bool event_triggered;
+	bool __data_racy event_triggered;
 
 	union {
 		/* Available for split ring */
-- 
MST