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Sun, 15 Nov 2026 15:07:39 -0800 (PST) X-Received: by 2002:a05:600c:8b6c:b0:4a3:5a7b:6002 with SMTP id 5b1f17b1804b1-4bb649d4148mr97699295e9.28.1794784058388; Sun, 15 Nov 2026 15:07:38 -0800 (PST) Received: from redhat.com ([2a0d:6fc0:151e:a200:7a96:1b15:81f:ebed]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4bb5b4a3fcdsm213451595e9.0.2026.11.15.15.07.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Nov 2026 15:07:37 -0800 (PST) Date: Sun, 15 Nov 2026 18:07:33 -0500 From: "Michael S. Tsirkin" To: Congjie Zhou Cc: netdev@vger.kernel.org, jasowangio@gmail.com, eperezma@redhat.com, xuanzhuo@linux.alibaba.com, andrew+netdev@lunn.ch, davem@davemloft.net, edumazet@kernel.org, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [BUG] virtio_net: RX stall caused by masking callbacks after NAPI ownership release Message-ID: <20261115175445-mutt-send-email-mst@kernel.org> References: X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Wed, Nov 11, 2026 at 09:36:10PM +0800, Congjie Zhou wrote: > Hello, > > I observed a persistent virtio-net RX stall on Linux 6.18.58 during a > multi-threaded TCP receive workload. After the stall, the RX virtqueue > contained unconsumed used entries, but its NAPI instance had no owner, > the NAPI timer was inactive and virtqueue notifications were disabled. > The receiving TCP threads remained blocked waiting for data. Played with it a bit since. I think the below should do it? Can you confirm? diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index dd2c41ef6fbe7..7bc7306231521 100644 --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -740,6 +740,8 @@ static bool virtqueue_napi_complete(struct napi_struct *napi, return true; } else { virtqueue_disable_cb(vq); + if (!napi_is_deferred(napi) && !napi_is_scheduled(napi)) + napi_schedule(napi); } return false; diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index c0ae442c4344b..2199750825d4f 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -22,6 +22,7 @@ #define _LINUX_NETDEVICE_H #include +#include #include #include #include @@ -553,6 +554,21 @@ static inline bool napi_is_scheduled(struct napi_struct *n) return test_bit(NAPI_STATE_SCHED, &n->state); } +/** + * napi_is_deferred - test if the NAPI timer is armed and will schedule NAPI + * @n: NAPI context + * + * A true answer guarantees NAPI will be polled again without driver + * action. A false answer is "best-effort": the timer can be armed + * right after the check. + * + * Return: True if timer is armed, False otherwise. + */ +static inline bool napi_is_deferred(struct napi_struct *n) +{ + return hrtimer_active(&n->timer); +} + bool napi_schedule_prep(struct napi_struct *n); /**