[PATCH v4 net-next 07/14] net: softnet_data: Make xmit.recursion per task.
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: 2024-06-04 15:44:52
Also in:
lkml
Subsystem:
networking drivers, networking [general], scheduler, the rest · Maintainers:
Andrew Lunn, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Ingo Molnar, Peter Zijlstra, Juri Lelli, Vincent Guittot, Linus Torvalds
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 <bsegall@google.com> Cc: Daniel Bristot de Oliveira <redacted> Cc: Dietmar Eggemann <dietmar.eggemann@arm.com> Cc: Juri Lelli <juri.lelli@redhat.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Valentin Schneider <vschneid@redhat.com> Cc: Vincent Guittot <vincent.guittot@linaro.org> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- 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 d20c6c99eb887..b5ec072ec2430 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h@@ -3223,7 +3223,9 @@ 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;
@@ -3256,10 +3258,19 @@ struct softnet_data { DECLARE_PER_CPU_ALIGNED(struct softnet_data, softnet_data); +#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 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 61591ac6eab6d..a9b0ca72db55f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h@@ -975,7 +975,9 @@ 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;
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); #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 #endif
--
2.45.1