From patchwork Fri Dec 15 17:07:27 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Andrzej Siewior X-Patchwork-Id: 13494688 X-Patchwork-Delegate: kuba@kernel.org 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 683CB4187D; Fri, 15 Dec 2023 17:10:37 +0000 (UTC) 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="QPPNb1XU"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="KDbhOqx2" From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1702660235; 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=Vs9x26/0xa1tcBYKbgQAR4XHVyOmk1j4LbahtbGEJ58=; b=QPPNb1XUv1JJZyXkWSJEfN4hs115WhG65vgXF8+eYS2NVCHUiR5bdf+0Te2De9CMkDVhX5 kg+4nxjhReF+U9wcdzwufFTgCeQwQjWs5e258Ldrv1vqqYXu667680eap2RXNzFS97oZ97 Hl80mYjI7MI1SsnnbfyfgeagmgvnlzY0xr283cnFTp45haOfEGAsbdu95tuNqd14AFBlLh IoqH0SrvRHQagmfhbpovRgr2lo+JMaXjSOlPqfVO52gdeCf/JjymwJKCmpvPAqjwoyc52q NsJz+5hhs3fygtd4N4fSYjKv7jyo4nbagYTuZK1T6MBDaNXVxUcOQLb/XpjnNg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1702660235; 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=Vs9x26/0xa1tcBYKbgQAR4XHVyOmk1j4LbahtbGEJ58=; b=KDbhOqx2pyNuV88W7bRpl2paKK1qKcH6+JJCM/aNDU55/cuO1o1cA8YMiXZu0qz812rB0f YrGOeFqrjm1A/SAQ== 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 08/24] net: softnet_data: Make xmit.recursion per task. Date: Fri, 15 Dec 2023 18:07:27 +0100 Message-ID: <20231215171020.687342-9-bigeasy@linutronix.de> In-Reply-To: <20231215171020.687342-1-bigeasy@linutronix.de> References: <20231215171020.687342-1-bigeasy@linutronix.de> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Delegate: kuba@kernel.org 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 | 30 +++++++++++++++++++++++++++++- include/linux/sched.h | 4 +++- 2 files changed, 32 insertions(+), 2 deletions(-) diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 2564e209465ea..06436695c3679 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h @@ -3260,7 +3260,9 @@ 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; @@ -3308,12 +3310,36 @@ static inline void input_queue_tail_incr_save(struct softnet_data *sd, DECLARE_PER_CPU_ALIGNED(struct softnet_data, softnet_data); +#define XMIT_RECURSION_LIMIT 8 +#ifdef CONFIG_PREEMPT_RT + +static inline int dev_recursion_level(void) +{ + return current->net_xmit_recursion; +} + +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 int dev_recursion_level(void) { return this_cpu_read(softnet_data.xmit.recursion); } -#define XMIT_RECURSION_LIMIT 8 static inline bool dev_xmit_recursion(void) { return unlikely(__this_cpu_read(softnet_data.xmit.recursion) > @@ -3330,6 +3356,8 @@ static inline void dev_xmit_recursion_dec(void) __this_cpu_dec(softnet_data.xmit.recursion); } +#endif + 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 292c316972485..26b1b7d674b5d 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -964,7 +964,9 @@ 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. */ struct restart_block restart_block;