[PATCH RT] net: move xmit_recursion to per-task variable on -RT
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: 2016-01-13 15:23:58
Also in:
linux-rt-users, 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
A softirq on -RT can be preempted. That means one task is in __dev_queue_xmit(), gets preempted and another task may enter __dev_queue_xmit() aw well. netperf together with a bridge device will then trigger the `recursion alert` because each task increments the xmit_recursion variable which is per-CPU. A virtual device like br0 is required to trigger this warning. This patch moves the counter to per task instead per-CPU so it counts the recursion properly on -RT. Cc: stable-rt@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- include/linux/netdevice.h | 9 +++++++++ include/linux/sched.h | 3 +++ net/core/dev.c | 41 ++++++++++++++++++++++++++++++++++++++--- 3 files changed, 50 insertions(+), 3 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index f14e39cb897c..4a8d3429dc12 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h@@ -2249,11 +2249,20 @@ void netdev_freemem(struct net_device *dev); void synchronize_net(void); int init_dummy_netdev(struct net_device *dev); +#ifdef CONFIG_PREEMPT_RT_FULL +static inline int dev_recursion_level(void) +{ + return atomic_read(¤t->xmit_recursion); +} + +#else + DECLARE_PER_CPU(int, xmit_recursion); static inline int dev_recursion_level(void) { return this_cpu_read(xmit_recursion); } +#endif struct net_device *dev_get_by_index(struct net *net, int ifindex); struct net_device *__dev_get_by_index(struct net *net, int ifindex);
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 04eb2f8bc274..5d36818107b0 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h@@ -1855,6 +1855,9 @@ struct task_struct { pte_t kmap_pte[KM_TYPE_NR]; # endif #endif +#ifdef CONFIG_PREEMPT_RT_FULL + atomic_t xmit_recursion; +#endif #ifdef CONFIG_DEBUG_ATOMIC_SLEEP unsigned long task_state_change; #endif
diff --git a/net/core/dev.c b/net/core/dev.c
index ae4a67e7e654..1f6a7e9a22c4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c@@ -2946,9 +2946,44 @@ static void skb_update_prio(struct sk_buff *skb) #define skb_update_prio(skb) #endif +#ifdef CONFIG_PREEMPT_RT_FULL + +static inline int xmit_rec_read(void) +{ + return atomic_read(¤t->xmit_recursion); +} + +static inline void xmit_rec_inc(void) +{ + atomic_inc(¤t->xmit_recursion); +} + +static inline void xmit_rec_dec(void) +{ + atomic_dec(¤t->xmit_recursion); +} + +#else + DEFINE_PER_CPU(int, xmit_recursion); EXPORT_SYMBOL(xmit_recursion); +static inline int xmit_rec_read(void) +{ + return __this_cpu_read(xmit_recursion); +} + +static inline void xmit_rec_inc(void) +{ + __this_cpu_inc(xmit_recursion); +} + +static inline int xmit_rec_dec(void) +{ + __this_cpu_dec(xmit_recursion); +} +#endif + #define RECURSION_LIMIT 10 /**
@@ -3141,7 +3176,7 @@ static int __dev_queue_xmit(struct sk_buff *skb, void *accel_priv) if (txq->xmit_lock_owner != cpu) { - if (__this_cpu_read(xmit_recursion) > RECURSION_LIMIT) + if (xmit_rec_read() > RECURSION_LIMIT) goto recursion_alert; skb = validate_xmit_skb(skb, dev);
@@ -3151,9 +3186,9 @@ static int __dev_queue_xmit(struct sk_buff *skb, void *accel_priv) HARD_TX_LOCK(dev, txq, cpu); if (!netif_xmit_stopped(txq)) { - __this_cpu_inc(xmit_recursion); + xmit_rec_inc(); skb = dev_hard_start_xmit(skb, dev, txq, &rc); - __this_cpu_dec(xmit_recursion); + xmit_rec_dec(); if (dev_xmit_complete(rc)) { HARD_TX_UNLOCK(dev, txq); goto out;
--
2.7.0.rc3