X-Git-Url: http://pilppa.org/gitweb/gitweb.cgi?a=blobdiff_plain;f=include%2Flinux%2Fseqlock.h;h=632205ccc25dabdd50debabc06914161bc2358ca;hb=4d36a9e65d4966b433b2f3424d9457468bc80e00;hp=52c9eb9b6df2b15af03ac0dc8a618bf0ad72e93a;hpb=874ff01bd9183ad16495acfd54e93a619d12b8b5;p=linux-2.6-omap-h63xx.git

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 52c9eb9b6df..632205ccc25 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -61,10 +61,10 @@ static inline void write_seqlock(seqlock_t *sl)
 {
 	spin_lock(&sl->lock);
 	++sl->sequence;
-	smp_wmb();			
-}	
+	smp_wmb();
+}
 
-static inline void write_sequnlock(seqlock_t *sl) 
+static inline void write_sequnlock(seqlock_t *sl)
 {
 	smp_wmb();
 	sl->sequence++;
@@ -77,7 +77,7 @@ static inline int write_tryseqlock(seqlock_t *sl)
 
 	if (ret) {
 		++sl->sequence;
-		smp_wmb();			
+		smp_wmb();
 	}
 	return ret;
 }
@@ -85,23 +85,29 @@ static inline int write_tryseqlock(seqlock_t *sl)
 /* Start of read calculation -- fetch last complete writer token */
 static __always_inline unsigned read_seqbegin(const seqlock_t *sl)
 {
-	unsigned ret = sl->sequence;
+	unsigned ret;
+
+repeat:
+	ret = sl->sequence;
 	smp_rmb();
+	if (unlikely(ret & 1)) {
+		cpu_relax();
+		goto repeat;
+	}
+
 	return ret;
 }
 
-/* Test if reader processed invalid data.
- * If initial values is odd, 
- *	then writer had already started when section was entered
- * If sequence value changed
- *	then writer changed data while in section
- *    
- * Using xor saves one conditional branch.
+/*
+ * Test if reader processed invalid data.
+ *
+ * If sequence value changed then writer changed data while in section.
  */
-static __always_inline int read_seqretry(const seqlock_t *sl, unsigned iv)
+static __always_inline int read_seqretry(const seqlock_t *sl, unsigned start)
 {
 	smp_rmb();
-	return (iv & 1) | (sl->sequence ^ iv);
+
+	return (sl->sequence != start);
 }
 
 
@@ -122,20 +128,26 @@ typedef struct seqcount {
 /* Start of read using pointer to a sequence counter only.  */
 static inline unsigned read_seqcount_begin(const seqcount_t *s)
 {
-	unsigned ret = s->sequence;
+	unsigned ret;
+
+repeat:
+	ret = s->sequence;
 	smp_rmb();
+	if (unlikely(ret & 1)) {
+		cpu_relax();
+		goto repeat;
+	}
 	return ret;
 }
 
-/* Test if reader processed invalid data.
- * Equivalent to: iv is odd or sequence number has changed.
- *                (iv & 1) || (*s != iv)
- * Using xor saves one conditional branch.
+/*
+ * Test if reader processed invalid data because sequence number has changed.
  */
-static inline int read_seqcount_retry(const seqcount_t *s, unsigned iv)
+static inline int read_seqcount_retry(const seqcount_t *s, unsigned start)
 {
 	smp_rmb();
-	return (iv & 1) | (s->sequence ^ iv);
+
+	return s->sequence != start;
 }