Re: [PATCH v2] virtio_ring: tag event_triggered as racy for KCSAN
From: Marco Elver <elver@google.com>
Date: 2024-09-12 15:12:26
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On Thu, 12 Sept 2024 at 17:02, Michael S. Tsirkin [off-list ref] wrote:
Setting event_triggered from the interrupt handler 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 can not figure all this out, and warns about the race between the write and the read. Tag the access data_racy for now. We should probably look at ways to make this more straight-forwardly correct. Cc: Marco Elver <elver@google.com> Reported-by: syzbot+8a02104389c2e0ef5049@syzkaller.appspotmail.com Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Probably more conservative than the __data_racy hammer: Acked-by: Marco Elver <elver@google.com>
quoted hunk ↗ jump to hunk
--- 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..98374ed7c577 100644 --- a/drivers/virtio/virtio_ring.c +++ b/drivers/virtio/virtio_ring.c@@ -2588,7 +2588,7 @@ irqreturn_t vring_interrupt(int irq, void *_vq) /* Just a hint for performance: so it's ok that this can be racy! */ if (vq->event) - vq->event_triggered = true; + data_race(vq->event_triggered = true); pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); if (vq->vq.callback) --MST