softirq: Check preemption after reenabling interrupts

raise_softirq_irqoff() disables interrupts and wakes the softirq
daemon, but after reenabling interrupts there is no preemption check,
so the execution of the softirq thread might be delayed arbitrarily.

In principle we could add that check to local_irq_enable/restore, but
that's overkill as the rasie_softirq_irqoff() sections are the only
ones which show this behaviour.

Reported-by: Carsten Emde <cbe@osadl.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable-rt@vger.kernel.org

4 files changed, 15 insertions, 0 deletions

diff --git a/block/blk-iopoll.c b/block/blk-iopoll.c
index 58916afbbda5..f7ca9b411d2a 100644
--- a/block/blk-iopoll.c
+++ b/block/blk-iopoll.c
@@ -38,6 +38,7 @@ void blk_iopoll_sched(struct blk_iopoll *iop)
 	list_add_tail(&iop->list, &__get_cpu_var(blk_cpu_iopoll));
 	__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 EXPORT_SYMBOL(blk_iopoll_sched);
 
@@ -135,6 +136,7 @@ static void blk_iopoll_softirq(struct softirq_action *h)
 		__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
 
 	local_irq_enable();
+	preempt_check_resched_rt();
 }
 
 /**
@@ -204,6 +206,7 @@ static int __cpuinit blk_iopoll_cpu_notify(struct notifier_block *self,
 				 &__get_cpu_var(blk_cpu_iopoll));
 		__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
 		local_irq_enable();
+		preempt_check_resched_rt();
 	}
 
 	return NOTIFY_OK;
diff --git a/block/blk-softirq.c b/block/blk-softirq.c
index 1366a89d8e66..60a88ab5f19e 100644
--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -50,6 +50,7 @@ static void trigger_softirq(void *data)
 		raise_softirq_irqoff(BLOCK_SOFTIRQ);
 
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 
 /*
@@ -92,6 +93,7 @@ static int __cpuinit blk_cpu_notify(struct notifier_block *self,
 				 &__get_cpu_var(blk_cpu_done));
 		raise_softirq_irqoff(BLOCK_SOFTIRQ);
 		local_irq_enable();
+		preempt_check_resched_rt();
 	}
 
 	return NOTIFY_OK;
@@ -150,6 +152,7 @@ do_local:
 		goto do_local;
 
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 
 /**
diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 6450c0113b5b..58d898278720 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -56,8 +56,10 @@ do { \
 
 #ifndef CONFIG_PREEMPT_RT_BASE
 # define preempt_enable_no_resched()	__preempt_enable_no_resched()
+# define preempt_check_resched_rt()	do { } while (0)
 #else
 # define preempt_enable_no_resched()	preempt_enable()
+# define preempt_check_resched_rt()	preempt_check_resched()
 #endif
 
 #define preempt_enable() \
@@ -105,6 +107,7 @@ do { \
 #define preempt_disable_notrace()		do { } while (0)
 #define preempt_enable_no_resched_notrace()	do { } while (0)
 #define preempt_enable_notrace()		do { } while (0)
+#define preempt_check_resched_rt()	do { } while (0)
 
 #endif /* CONFIG_PREEMPT_COUNT */
 
diff --git a/net/core/dev.c b/net/core/dev.c
index e554093042a0..034be6c3d7d9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1779,6 +1779,7 @@ static inline void __netif_reschedule(struct Qdisc *q)
 	sd->output_queue_tailp = &q->next_sched;
 	raise_softirq_irqoff(NET_TX_SOFTIRQ);
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 
 void __netif_schedule(struct Qdisc *q)
@@ -1800,6 +1801,7 @@ void dev_kfree_skb_irq(struct sk_buff *skb)
 		sd->completion_queue = skb;
 		raise_softirq_irqoff(NET_TX_SOFTIRQ);
 		local_irq_restore(flags);
+		preempt_check_resched_rt();
 	}
 }
 EXPORT_SYMBOL(dev_kfree_skb_irq);
@@ -2969,6 +2971,7 @@ enqueue:
 	rps_unlock(sd);
 
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 
 	atomic_long_inc(&skb->dev->rx_dropped);
 	kfree_skb(skb);
@@ -3789,6 +3792,7 @@ static void net_rps_action_and_irq_enable(struct softnet_data *sd)
 	} else
 #endif
 		local_irq_enable();
+	preempt_check_resched_rt();
 }
 
 static int process_backlog(struct napi_struct *napi, int quota)
@@ -3861,6 +3865,7 @@ void __napi_schedule(struct napi_struct *n)
 	local_irq_save(flags);
 	____napi_schedule(&__get_cpu_var(softnet_data), n);
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 EXPORT_SYMBOL(__napi_schedule);
 
@@ -6401,6 +6406,7 @@ static int dev_cpu_callback(struct notifier_block *nfb,
 
 	raise_softirq_irqoff(NET_TX_SOFTIRQ);
 	local_irq_enable();
+	preempt_check_resched_rt();
 
 	/* Process offline CPU's input_pkt_queue */
 	while ((skb = __skb_dequeue(&oldsd->process_queue))) {