3 files changed, 48 insertions, 13 deletions

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 21a2093..142c0f7 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -152,18 +152,30 @@ static inline int read_seqcount_retry(const seqcount_t *s, unsigned start)
  * Sequence counter only version assumes that callers are using their
  * own mutexing.
  */
-static inline void write_seqcount_begin(seqcount_t *s)
+static inline void __write_seqcount_begin(seqcount_t *s)
 {
 	s->sequence++;
 	smp_wmb();
 }
 
-static inline void write_seqcount_end(seqcount_t *s)
+static inline void write_seqcount_begin(seqcount_t *s)
+{
+	preempt_disable_rt();
+	__write_seqcount_begin(s);
+}
+
+static inline void __write_seqcount_end(seqcount_t *s)
 {
 	smp_wmb();
 	s->sequence++;
 }
 
+static inline void write_seqcount_end(seqcount_t *s)
+{
+	__write_seqcount_end(s);
+	preempt_enable_rt();
+}
+
 /**
  * write_seqcount_barrier - invalidate in-progress read-side seq operations
  * @s: pointer to seqcount_t
@@ -204,10 +216,33 @@ typedef struct {
 /*
  * Read side functions for starting and finalizing a read side section.
  */
+#ifndef CONFIG_PREEMPT_RT_FULL
 static inline unsigned read_seqbegin(const seqlock_t *sl)
 {
 	return read_seqcount_begin(&sl->seqcount);
 }
+#else
+/*
+ * Starvation safe read side for RT
+ */
+static inline unsigned read_seqbegin(seqlock_t *sl)
+{
+	unsigned ret;
+
+repeat:
+	ret = ACCESS_ONCE(sl->seqcount.sequence);
+	if (unlikely(ret & 1)) {
+		/*
+		 * Take the lock and let the writer proceed (i.e. evtl
+		 * boost it), otherwise we could loop here forever.
+		 */
+		spin_lock(&sl->lock);
+		spin_unlock(&sl->lock);
+		goto repeat;
+	}
+	return ret;
+}
+#endif
 
 static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
 {
@@ -222,36 +257,36 @@ static inline unsigned read_seqretry(const seqlock_t *sl, unsigned start)
 static inline void write_seqlock(seqlock_t *sl)
 {
 	spin_lock(&sl->lock);
-	write_seqcount_begin(&sl->seqcount);
+	__write_seqcount_begin(&sl->seqcount);
 }
 
 static inline void write_sequnlock(seqlock_t *sl)
 {
-	write_seqcount_end(&sl->seqcount);
+	__write_seqcount_end(&sl->seqcount);
 	spin_unlock(&sl->lock);
 }
 
 static inline void write_seqlock_bh(seqlock_t *sl)
 {
 	spin_lock_bh(&sl->lock);
-	write_seqcount_begin(&sl->seqcount);
+	__write_seqcount_begin(&sl->seqcount);
 }
 
 static inline void write_sequnlock_bh(seqlock_t *sl)
 {
-	write_seqcount_end(&sl->seqcount);
+	__write_seqcount_end(&sl->seqcount);
 	spin_unlock_bh(&sl->lock);
 }
 
 static inline void write_seqlock_irq(seqlock_t *sl)
 {
 	spin_lock_irq(&sl->lock);
-	write_seqcount_begin(&sl->seqcount);
+	__write_seqcount_begin(&sl->seqcount);
 }
 
 static inline void write_sequnlock_irq(seqlock_t *sl)
 {
-	write_seqcount_end(&sl->seqcount);
+	__write_seqcount_end(&sl->seqcount);
 	spin_unlock_irq(&sl->lock);
 }
 
@@ -260,7 +295,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
 	unsigned long flags;
 
 	spin_lock_irqsave(&sl->lock, flags);
-	write_seqcount_begin(&sl->seqcount);
+	__write_seqcount_begin(&sl->seqcount);
 	return flags;
 }
 
@@ -270,7 +305,7 @@ static inline unsigned long __write_seqlock_irqsave(seqlock_t *sl)
 static inline void
 write_sequnlock_irqrestore(seqlock_t *sl, unsigned long flags)
 {
-	write_seqcount_end(&sl->seqcount);
+	__write_seqcount_end(&sl->seqcount);
 	spin_unlock_irqrestore(&sl->lock, flags);
 }
 
diff --git a/include/net/dst.h b/include/net/dst.h
index 9c12376..2322201 100644
--- a/include/net/dst.h
+++ b/include/net/dst.h
@@ -395,7 +395,7 @@ static inline void dst_confirm(struct dst_entry *dst)
 static inline int dst_neigh_output(struct dst_entry *dst, struct neighbour *n,
 				   struct sk_buff *skb)
 {
-	const struct hh_cache *hh;
+	struct hh_cache *hh;
 
 	if (dst->pending_confirm) {
 		unsigned long now = jiffies;
diff --git a/include/net/neighbour.h b/include/net/neighbour.h
index 536501a..a9d84bf 100644
--- a/include/net/neighbour.h
+++ b/include/net/neighbour.h
@@ -333,7 +333,7 @@ static inline int neigh_hh_bridge(struct hh_cache *hh, struct sk_buff *skb)
 }
 #endif
 
-static inline int neigh_hh_output(const struct hh_cache *hh, struct sk_buff *skb)
+static inline int neigh_hh_output(struct hh_cache *hh, struct sk_buff *skb)
 {
 	unsigned int seq;
 	int hh_len;
@@ -388,7 +388,7 @@ struct neighbour_cb {
 
 #define NEIGH_CB(skb)	((struct neighbour_cb *)(skb)->cb)
 
-static inline void neigh_ha_snapshot(char *dst, const struct neighbour *n,
+static inline void neigh_ha_snapshot(char *dst, struct neighbour *n,
 				     const struct net_device *dev)
 {
 	unsigned int seq;