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[79.179.105.63]) by smtp.gmail.com with ESMTPSA id 65sm20037688wre.6.2020.08.01.23.26.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 01 Aug 2020 23:26:18 -0700 (PDT) Date: Sun, 2 Aug 2020 02:26:16 -0400 From: "Michael S. Tsirkin" To: Mao Wenan Cc: jasowang@redhat.com, virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org Subject: Re: [PATCH -next v2] virtio_net: Avoid loop in virtnet_poll Message-ID: <20200802022549-mutt-send-email-mst@kernel.org> References: <20200802003818-mutt-send-email-mst@kernel.org> <1596347793-55894-1-git-send-email-wenan.mao@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1596347793-55894-1-git-send-email-wenan.mao@linux.alibaba.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Just noticed the subject is wrong: this is no longer a virtio_net patch. On Sun, Aug 02, 2020 at 01:56:33PM +0800, Mao Wenan wrote: > The loop may exist if vq->broken is true, > virtqueue_get_buf_ctx_packed or virtqueue_get_buf_ctx_split > will return NULL, so virtnet_poll will reschedule napi to > receive packet, it will lead cpu usage(si) to 100%. > > call trace as below: > virtnet_poll > virtnet_receive > virtqueue_get_buf_ctx > virtqueue_get_buf_ctx_packed > virtqueue_get_buf_ctx_split > virtqueue_napi_complete > virtqueue_poll //return true > virtqueue_napi_schedule //it will reschedule napi > > To fix this, return false if vq is broken in virtqueue_poll. > > Signed-off-by: Mao Wenan > --- > v1->v2: fix it in virtqueue_poll suggested by Michael S. Tsirkin > drivers/virtio/virtio_ring.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c > index 58b96ba..4f7c73e 100644 > --- a/drivers/virtio/virtio_ring.c > +++ b/drivers/virtio/virtio_ring.c > @@ -1960,6 +1960,9 @@ bool virtqueue_poll(struct virtqueue *_vq, unsigned last_used_idx) > { > struct vring_virtqueue *vq = to_vvq(_vq); > > + if (unlikely(vq->broken)) > + return false; > + > virtio_mb(vq->weak_barriers); > return vq->packed_ring ? virtqueue_poll_packed(_vq, last_used_idx) : > virtqueue_poll_split(_vq, last_used_idx); > -- > 1.8.3.1