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>

4 files changed, 16 insertions, 0 deletions

diff --git a/block/blk-iopoll.c b/block/blk-iopoll.c
index 0736729d64941..3e21e31d0d7ec 100644
--- a/block/blk-iopoll.c
+++ b/block/blk-iopoll.c
@@ -35,6 +35,7 @@ void blk_iopoll_sched(struct blk_iopoll *iop)
 	list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
 	__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 EXPORT_SYMBOL(blk_iopoll_sched);
 
@@ -132,6 +133,7 @@ static void blk_iopoll_softirq(struct softirq_action *h)
 		__raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
 
 	local_irq_enable();
+	preempt_check_resched_rt();
 }
 
 /**
@@ -201,6 +203,7 @@ static int blk_iopoll_cpu_notify(struct notifier_block *self,
 				 this_cpu_ptr(&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 53b1737e978d5..81c3c0a62edfa 100644
--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -51,6 +51,7 @@ static void trigger_softirq(void *data)
 		raise_softirq_irqoff(BLOCK_SOFTIRQ);
 
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 
 /*
@@ -93,6 +94,7 @@ static int blk_cpu_notify(struct notifier_block *self, unsigned long action,
 				 this_cpu_ptr(&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 210bd26b1882d..2b761d0c89d6c 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -160,8 +160,10 @@ do { \
 
 #ifdef CONFIG_PREEMPT_RT_BASE
 # define preempt_enable_no_resched() sched_preempt_enable_no_resched()
+# define preempt_check_resched_rt() preempt_check_resched()
 #else
 # define preempt_enable_no_resched() preempt_enable()
+# define preempt_check_resched_rt() barrier();
 #endif
 
 #define preemptible()	(preempt_count() == 0 && !irqs_disabled())
@@ -232,6 +234,7 @@ do { \
 #define preempt_disable_notrace()		barrier()
 #define preempt_enable_no_resched_notrace()	barrier()
 #define preempt_enable_notrace()		barrier()
+#define preempt_check_resched_rt()		barrier()
 #define preemptible()				0
 
 #endif /* CONFIG_PREEMPT_COUNT */
diff --git a/net/core/dev.c b/net/core/dev.c
index 7f00f24397700..1d5fe14d727f9 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2246,6 +2246,7 @@ 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)
@@ -2327,6 +2328,7 @@ void __dev_kfree_skb_irq(struct sk_buff *skb, enum skb_free_reason reason)
 	__this_cpu_write(softnet_data.completion_queue, skb);
 	raise_softirq_irqoff(NET_TX_SOFTIRQ);
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 EXPORT_SYMBOL(__dev_kfree_skb_irq);
 
@@ -3524,6 +3526,7 @@ drop:
 	rps_unlock(sd);
 
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 
 	atomic_long_inc(&skb->dev->rx_dropped);
 	kfree_skb(skb);
@@ -4512,6 +4515,7 @@ static void net_rps_action_and_irq_enable(struct softnet_data *sd)
 		sd->rps_ipi_list = NULL;
 
 		local_irq_enable();
+		preempt_check_resched_rt();
 
 		/* Send pending IPI's to kick RPS processing on remote cpus. */
 		while (remsd) {
@@ -4525,6 +4529,7 @@ static void net_rps_action_and_irq_enable(struct softnet_data *sd)
 	} else
 #endif
 		local_irq_enable();
+	preempt_check_resched_rt();
 }
 
 static bool sd_has_rps_ipi_waiting(struct softnet_data *sd)
@@ -4606,6 +4611,7 @@ void __napi_schedule(struct napi_struct *n)
 	local_irq_save(flags);
 	____napi_schedule(this_cpu_ptr(&softnet_data), n);
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 EXPORT_SYMBOL(__napi_schedule);
 
@@ -7454,6 +7460,7 @@ 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))) {