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[2a02:3100:b2b3:101:b51c:a607:3dcc:3979]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a01f9248ccsm3513165e9.3.2026.09.30.12.21.26 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Wed, 30 Sep 2026 12:21:26 -0700 (PDT) From: Karl Mehltretter To: netdev@vger.kernel.org Cc: Karl Mehltretter , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , Stephen Hemminger , Arend van Spriel , linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, stable@vger.kernel.org Subject: [PATCH net v2 2/2] netpoll: avoid blocking on the transmit lock in queue_process Date: Wed, 30 Sep 2026 21:21:03 +0200 Message-Id: <20260930192103.62973-3-kmehltretter@gmail.com> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20260928064239.32456-1-kmehltretter@gmail.com> References: <20260928064239.32456-1-kmehltretter@gmail.com> Precedence: bulk X-Mailing-List: linux-rt-devel@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit queue_process() disables interrupts before taking the device transmit lock with HARD_TX_LOCK(). The lock may sleep on PREEMPT_RT: BUG: sleeping function called from invalid context in_atomic(): 0, irqs_disabled(): 1, non_block: 0 Workqueue: events queue_process rt_spin_lock queue_process process_one_work Use HARD_TX_TRYLOCK() instead. If another CPU owns the lock, put the skb back at the head of the deferred queue, restore interrupts and retry on the next tick. Keep the longer HZ / 10 backoff for a stopped transmit queue or a driver which returns busy. Fixes: 3640543df26f ("[PATCH] netpoll: fix netpoll lockup") Cc: stable@vger.kernel.org # 6.12+ Assisted-by: LLM Signed-off-by: Karl Mehltretter --- net/core/netpoll.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/net/core/netpoll.c b/net/core/netpoll.c index e0cfcb05468e2..8d8e3c33cfdfe 100644 --- a/net/core/netpoll.c +++ b/net/core/netpoll.c @@ -166,7 +166,13 @@ static void queue_process(struct work_struct *work) skb_set_queue_mapping(skb, q_index); } txq = netdev_get_tx_queue(dev, q_index); - HARD_TX_LOCK(dev, txq, smp_processor_id()); + if (!HARD_TX_TRYLOCK(dev, txq)) { + netpoll_txq_queue_head(npinfo, skb); + local_irq_restore(flags); + + schedule_delayed_work(&npinfo->tx_work, 1); + return; + } if (netif_xmit_frozen_or_stopped(txq) || !dev_xmit_complete(netpoll_start_xmit(skb, dev, txq))) { netpoll_txq_queue_head(npinfo, skb); -- 2.53.0