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-rw-r--r--include/linux/seqlock.h47
1 files changed, 44 insertions, 3 deletions
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 5f68d0a391ce..486e685a226a 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -233,6 +233,47 @@ static inline void raw_write_seqcount_end(seqcount_t *s)
s->sequence++;
}
+/**
+ * raw_write_seqcount_barrier - do a seq write barrier
+ * @s: pointer to seqcount_t
+ *
+ * This can be used to provide an ordering guarantee instead of the
+ * usual consistency guarantee. It is one wmb cheaper, because we can
+ * collapse the two back-to-back wmb()s.
+ *
+ * seqcount_t seq;
+ * bool X = true, Y = false;
+ *
+ * void read(void)
+ * {
+ * bool x, y;
+ *
+ * do {
+ * int s = read_seqcount_begin(&seq);
+ *
+ * x = X; y = Y;
+ *
+ * } while (read_seqcount_retry(&seq, s));
+ *
+ * BUG_ON(!x && !y);
+ * }
+ *
+ * void write(void)
+ * {
+ * Y = true;
+ *
+ * raw_write_seqcount_barrier(seq);
+ *
+ * X = false;
+ * }
+ */
+static inline void raw_write_seqcount_barrier(seqcount_t *s)
+{
+ s->sequence++;
+ smp_wmb();
+ s->sequence++;
+}
+
/*
* raw_write_seqcount_latch - redirect readers to even/odd copy
* @s: pointer to seqcount_t
@@ -266,13 +307,13 @@ static inline void write_seqcount_end(seqcount_t *s)
}
/**
- * write_seqcount_barrier - invalidate in-progress read-side seq operations
+ * write_seqcount_invalidate - invalidate in-progress read-side seq operations
* @s: pointer to seqcount_t
*
- * After write_seqcount_barrier, no read-side seq operations will complete
+ * After write_seqcount_invalidate, no read-side seq operations will complete
* successfully and see data older than this.
*/
-static inline void write_seqcount_barrier(seqcount_t *s)
+static inline void write_seqcount_invalidate(seqcount_t *s)
{
smp_wmb();
s->sequence+=2;