Messages in this thread | | | Date | Wed, 27 Mar 2024 10:01:35 +1000 | Subject | Re: [PATCH] virtio_ring: Fix the stale index in available ring | From | Gavin Shan <> |
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On 3/27/24 09:14, Gavin Shan wrote: > On 3/27/24 01:46, Will Deacon wrote: >> On Tue, Mar 26, 2024 at 11:43:13AM +0000, Will Deacon wrote: >> >> Ok, long shot after eyeballing the vhost code, but does the diff below >> help at all? It looks like vhost_vq_avail_empty() can advance the value >> saved in 'vq->avail_idx' but without the read barrier, possibly confusing >> vhost_get_vq_desc() in polling mode. >> >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c >> index 045f666b4f12..87bff710331a 100644 >> --- a/drivers/vhost/vhost.c >> +++ b/drivers/vhost/vhost.c >> @@ -2801,6 +2801,7 @@ bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq) >> return false; >> vq->avail_idx = vhost16_to_cpu(vq, avail_idx); >> + smp_rmb(); >> return vq->avail_idx == vq->last_avail_idx; >> } >> EXPORT_SYMBOL_GPL(vhost_vq_avail_empty); >> > > Thanks, Will. I already noticed smp_rmb() has been missed in vhost_vq_avail_empty(). > The issue still exists after smp_rmb() is added here. However, I'm inspired by your > suggestion and recheck the code again. It seems another smp_rmb() has been missed > in vhost_enable_notify(). > > With smp_rmb() added to vhost_vq_avail_empty() and vhost_enable_notify(), I'm unable > to hit the issue. I will try for more times to make sure the issue is really resolved. > After that, I will post formal patches for review. >
Thanks again, Will. The formal patches have been sent for review.
https://lkml.org/lkml/2024/3/27/40
Thanks, Gavin
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