#define __LINUX_SEQLOCK_H
/*
* Reader/writer consistent mechanism without starving writers. This type of
- * lock for data where the reader wants a consitent set of information
+ * lock for data where the reader wants a consistent set of information
* and is willing to retry if the information changes. Readers never
* block but they may have to retry if a writer is in
* progress. Writers do not wait for readers.
{
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++;
if (ret) {
++sl->sequence;
- smp_wmb();
+ smp_wmb();
}
return ret;
}
/* 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);
}
/* 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;
}