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Tsirkin" , virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, yihyu@redhat.com, shan.gavin@gmail.com, linux-arm-kernel@lists.infradead.org, Catalin Marinas , mochs@nvidia.com References: <35a6bcef-27cf-4626-a41d-9ec0a338fe28@redhat.com> <20240319182251.GB3121@willie-the-truck> <9500adaf-0075-4ae9-92db-7e310b6598b0@redhat.com> <20240319203540-mutt-send-email-mst@kernel.org> <3a6c8b23-af9c-47a7-8c22-8e0a78154bd3@redhat.com> <20240320030215-mutt-send-email-mst@kernel.org> <1dcec730-ec26-46f4-ba4c-06101fcc599e@redhat.com> <20240326033809-mutt-send-email-mst@kernel.org> <20240326114313.GA9482@willie-the-truck> <20240326154628.GA9613@willie-the-truck> From: Gavin Shan In-Reply-To: <20240326154628.GA9613@willie-the-truck> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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, Gavin