From: Thomas Gleixner <tglx@linutronix.de>
Date: Sun, 13 Nov 2011 17:17:09 +0100
Subject: softirq: Check preemption after reenabling interrupts
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: 83fd65a1189c37ab1bf127f6da58874318abbd4f
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

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>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 block/blk-softirq.c     |    3 +++
 include/linux/preempt.h |    3 +++
 lib/irq_poll.c          |    5 +++++
 net/core/dev.c          |    7 +++++++
 4 files changed, 18 insertions(+)

--- a/block/blk-softirq.c
+++ b/block/blk-softirq.c
@@ -52,6 +52,7 @@ static void trigger_softirq(void *data)
 		raise_softirq_irqoff(BLOCK_SOFTIRQ);
 
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 
 /*
@@ -90,6 +91,7 @@ static int blk_softirq_cpu_dead(unsigned
 			 this_cpu_ptr(&blk_cpu_done));
 	raise_softirq_irqoff(BLOCK_SOFTIRQ);
 	local_irq_enable();
+	preempt_check_resched_rt();
 
 	return 0;
 }
@@ -141,6 +143,7 @@ do_local:
 		goto do_local;
 
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 EXPORT_SYMBOL(__blk_complete_request);
 
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -186,8 +186,10 @@ 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())
@@ -274,6 +276,7 @@ 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
 
 #define migrate_disable()			barrier()
--- a/lib/irq_poll.c
+++ b/lib/irq_poll.c
@@ -36,6 +36,7 @@ void irq_poll_sched(struct irq_poll *iop
 	list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
 	__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 EXPORT_SYMBOL(irq_poll_sched);
 
@@ -71,6 +72,7 @@ void irq_poll_complete(struct irq_poll *
 	local_irq_save(flags);
 	__irq_poll_complete(iop);
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 EXPORT_SYMBOL(irq_poll_complete);
 
@@ -95,6 +97,7 @@ static void __latent_entropy irq_poll_so
 		}
 
 		local_irq_enable();
+		preempt_check_resched_rt();
 
 		/* Even though interrupts have been re-enabled, this
 		 * access is safe because interrupts can only add new
@@ -132,6 +135,7 @@ static void __latent_entropy irq_poll_so
 		__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
 
 	local_irq_enable();
+	preempt_check_resched_rt();
 }
 
 /**
@@ -195,6 +199,7 @@ static int irq_poll_cpu_dead(unsigned in
 			 this_cpu_ptr(&blk_cpu_iopoll));
 	__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
 	local_irq_enable();
+	preempt_check_resched_rt();
 
 	return 0;
 }
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2663,6 +2663,7 @@ static void __netif_reschedule(struct Qd
 	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)
@@ -2725,6 +2726,7 @@ void __dev_kfree_skb_irq(struct sk_buff
 	__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);
 
@@ -4215,6 +4217,7 @@ drop:
 	rps_unlock(sd);
 
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 
 	atomic_long_inc(&skb->dev->rx_dropped);
 	kfree_skb(skb);
@@ -5757,12 +5760,14 @@ static void net_rps_action_and_irq_enabl
 		sd->rps_ipi_list = NULL;
 
 		local_irq_enable();
+		preempt_check_resched_rt();
 
 		/* Send pending IPI's to kick RPS processing on remote cpus. */
 		net_rps_send_ipi(remsd);
 	} else
 #endif
 		local_irq_enable();
+	preempt_check_resched_rt();
 }
 
 static bool sd_has_rps_ipi_waiting(struct softnet_data *sd)
@@ -5840,6 +5845,7 @@ void __napi_schedule(struct napi_struct
 	local_irq_save(flags);
 	____napi_schedule(this_cpu_ptr(&softnet_data), n);
 	local_irq_restore(flags);
+	preempt_check_resched_rt();
 }
 EXPORT_SYMBOL(__napi_schedule);
 
@@ -9189,6 +9195,7 @@ static int dev_cpu_dead(unsigned int old
 
 	raise_softirq_irqoff(NET_TX_SOFTIRQ);
 	local_irq_enable();
+	preempt_check_resched_rt();
 
 #ifdef CONFIG_RPS
 	remsd = oldsd->rps_ipi_list;