From nobody Wed Dec 17 21:16:03 2025 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7872E157E6C; Fri, 3 May 2024 18:30:10 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714761012; cv=none; b=d0IsmYxi9fYvmyYRZToZ8QfjIcA7io7b0S14t/Nuca2tNjvRwJ5euatH0iyyE1KRFVbIhqZNhqCMBUl+QmrSvExLEMNTjWK8E/ipcTGrT4tdIwN87y/yyzkhdXOyHPrQeh9B+0wuCe53oucPwYHrUZHdCxeHkT0beDjfkhwIp/I= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1714761012; c=relaxed/simple; bh=0ek9e1xkSu9ugJNGW/WQGFdfj6oRd6gAc/VlLaOX934=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=nLJV/s+adFwKlhYFN3kTZFwE31uarUHA7AquU12R017np2lETM6niw6jAmDhruEA0fquNhLnygCP+q5X3vL0NDt9KdGMXPkcYvNIImA1Z72k7f//sUECey/JQoNVwa8HYwVgA75hRwD/1gmBulQFErN1QV0BXGvinPERHSJl7gc= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=hYNnkDu/; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=h4PyCzf+; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="hYNnkDu/"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="h4PyCzf+" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1714761008; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=W12KgBST4nx2eve2nFTDwC2VpCtYmoeYSIe9gYf7jLU=; b=hYNnkDu/YEIkbMmlcXSrr3zUKVjI0lBbG6xwH8ZICrBAHKq2h9Y0QNnOvxQlhNvhwS7Cph lDweOre4LmCytwQLo0zojT6Bboy9yAl+try72DiqCSsZxTgat7elEodRt7Fp54b+qbaY8l TOWtuyBj5bLqis8pgaK0m4ZF4EXp9p3ra7V5nZOApqeP3V+wM/0/7r7nEN/GX5srHe7E6T u7jyg78ZGy4IOPNiJ5X2mqWZ1sYs57ZJk8cTMKGKymdxVrwt4Lem0YD9EBiznNQ6gREzHP c/6nY0QOXAXeoM4hrNCsQbLAED2yZHKUogV/kTnfguxeDEpqHxm8aByRMv9H+Q== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1714761008; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=W12KgBST4nx2eve2nFTDwC2VpCtYmoeYSIe9gYf7jLU=; b=h4PyCzf+pnGgWSsUNbwR4a3djIi273FCLgVuwKNb1yWnxRnZ4OU0CTPr6DranJvPH9o5cW WV4AeZ+T70BCCwCg== To: linux-kernel@vger.kernel.org, netdev@vger.kernel.org Cc: "David S. Miller" , Boqun Feng , Daniel Borkmann , Eric Dumazet , Frederic Weisbecker , Ingo Molnar , Jakub Kicinski , Paolo Abeni , Peter Zijlstra , Thomas Gleixner , Waiman Long , Will Deacon , Sebastian Andrzej Siewior , Ben Segall , Daniel Bristot de Oliveira , Dietmar Eggemann , Juri Lelli , Mel Gorman , Steven Rostedt , Valentin Schneider , Vincent Guittot Subject: [PATCH net-next 08/15] net: softnet_data: Make xmit.recursion per task. Date: Fri, 3 May 2024 20:25:12 +0200 Message-ID: <20240503182957.1042122-9-bigeasy@linutronix.de> In-Reply-To: <20240503182957.1042122-1-bigeasy@linutronix.de> References: <20240503182957.1042122-1-bigeasy@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Softirq is preemptible on PREEMPT_RT. Without a per-CPU lock in local_bh_disable() there is no guarantee that only one device is transmitting at a time. With preemption and multiple senders it is possible that the per-CPU recursion counter gets incremented by different threads and exceeds XMIT_RECURSION_LIMIT leading to a false positive recursion alert. Instead of adding a lock to protect the per-CPU variable it is simpler to make the counter per-task. Sending and receiving skbs happens always in thread context anyway. Having a lock to protected the per-CPU counter would block/ serialize two sending threads needlessly. It would also require a recursive lock to ensure that the owner can increment the counter further. Make the recursion counter a task_struct member on PREEMPT_RT. Cc: Ben Segall Cc: Daniel Bristot de Oliveira Cc: Dietmar Eggemann Cc: Juri Lelli Cc: Mel Gorman Cc: Steven Rostedt Cc: Valentin Schneider Cc: Vincent Guittot Signed-off-by: Sebastian Andrzej Siewior --- include/linux/netdevice.h | 11 +++++++++++ include/linux/sched.h | 4 +++- net/core/dev.h | 20 ++++++++++++++++++++ 3 files changed, 34 insertions(+), 1 deletion(-) diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 41853424b41d7..c551ec235f9af 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -3222,7 +3222,9 @@ struct softnet_data { #endif /* written and read only by owning cpu: */ struct { +#ifndef CONFIG_PREEMPT_RT u16 recursion; +#endif u8 more; #ifdef CONFIG_NET_EGRESS u8 skip_txqueue; @@ -3255,10 +3257,19 @@ struct softnet_data { =20 DECLARE_PER_CPU_ALIGNED(struct softnet_data, softnet_data); =20 +#ifdef CONFIG_PREEMPT_RT +static inline int dev_recursion_level(void) +{ + return current->net_xmit_recursion; +} + +#else + static inline int dev_recursion_level(void) { return this_cpu_read(softnet_data.xmit.recursion); } +#endif =20 void __netif_schedule(struct Qdisc *q); void netif_schedule_queue(struct netdev_queue *txq); diff --git a/include/linux/sched.h b/include/linux/sched.h index 3c2abbc587b49..6779d3b8f2578 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -969,7 +969,9 @@ struct task_struct { /* delay due to memory thrashing */ unsigned in_thrashing:1; #endif - +#ifdef CONFIG_PREEMPT_RT + u8 net_xmit_recursion; +#endif unsigned long atomic_flags; /* Flags requiring atomic access. */ =20 struct restart_block restart_block; diff --git a/net/core/dev.h b/net/core/dev.h index b7b518bc2be55..2f96d63053ad0 100644 --- a/net/core/dev.h +++ b/net/core/dev.h @@ -150,6 +150,25 @@ struct napi_struct *napi_by_id(unsigned int napi_id); void kick_defer_list_purge(struct softnet_data *sd, unsigned int cpu); =20 #define XMIT_RECURSION_LIMIT 8 + +#ifdef CONFIG_PREEMPT_RT +static inline bool dev_xmit_recursion(void) +{ + return unlikely(current->net_xmit_recursion > XMIT_RECURSION_LIMIT); +} + +static inline void dev_xmit_recursion_inc(void) +{ + current->net_xmit_recursion++; +} + +static inline void dev_xmit_recursion_dec(void) +{ + current->net_xmit_recursion--; +} + +#else + static inline bool dev_xmit_recursion(void) { return unlikely(__this_cpu_read(softnet_data.xmit.recursion) > @@ -165,5 +184,6 @@ static inline void dev_xmit_recursion_dec(void) { __this_cpu_dec(softnet_data.xmit.recursion); } +#endif =20 #endif --=20 2.43.0