virtio_ring: Fix data race by tagging event_triggered as racy for KCSAN

In the Linux kernel, the following vulnerability has been resolved:

virtio_ring: Fix data race by tagging event_triggered as racy for KCSAN

syzbot reports a data-race when accessing the event_triggered, here is the

simplified stack when the issue occurred:

==================================================================

BUG: KCSAN: data-race in virtqueue_disable_cb / virtqueue_enable_cb_delayed

write to 0xffff8881025bc452 of 1 bytes by task 3288 on cpu 0:

virtqueue_enable_cb_delayed+0x42/0x3c0 drivers/virtio/virtio_ring.c:2653

start_xmit+0x230/0x1310 drivers/net/virtio_net.c:3264

__netdev_start_xmit include/linux/netdevice.h:5151 [inline]

netdev_start_xmit include/linux/netdevice.h:5160 [inline]

xmit_one net/core/dev.c:3800 [inline]

read to 0xffff8881025bc452 of 1 bytes by interrupt on cpu 1:

virtqueue_disable_cb_split drivers/virtio/virtio_ring.c:880 [inline]

virtqueue_disable_cb+0x92/0x180 drivers/virtio/virtio_ring.c:2566

skb_xmit_done+0x5f/0x140 drivers/net/virtio_net.c:777

vring_interrupt+0x161/0x190 drivers/virtio/virtio_ring.c:2715

__handle_irq_event_percpu+0x95/0x490 kernel/irq/handle.c:158

handle_irq_event_percpu kernel/irq/handle.c:193 [inline]

value changed: 0x01 -> 0x00

==================================================================

When the data race occurs, the function virtqueue_enable_cb_delayed() sets

event_triggered to false, and virtqueue_disable_cb_split/packed() reads it

as false due to the race condition. Since event_triggered is an unreliable

hint used for optimization, this should only cause the driver temporarily

suggest that the device not send an interrupt notification when the event

index is used.

Fix this KCSAN reported data-race issue by explicitly tagging the access as

data_racy.