Merge commit 'v3.5-rc2' into next

1 files changed, 22 insertions, 1 deletions

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index c6db9fb33c44..600060e25ec6 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -141,7 +141,7 @@ static inline unsigned __read_seqcount_begin(const seqcount_t *s)
 	unsigned ret;
 
 repeat:
-	ret = s->sequence;
+	ret = ACCESS_ONCE(s->sequence);
 	if (unlikely(ret & 1)) {
 		cpu_relax();
 		goto repeat;
@@ -166,6 +166,27 @@ static inline unsigned read_seqcount_begin(const seqcount_t *s)
 }
 
 /**
+ * raw_seqcount_begin - begin a seq-read critical section
+ * @s: pointer to seqcount_t
+ * Returns: count to be passed to read_seqcount_retry
+ *
+ * raw_seqcount_begin opens a read critical section of the given seqcount.
+ * Validity of the critical section is tested by checking read_seqcount_retry
+ * function.
+ *
+ * Unlike read_seqcount_begin(), this function will not wait for the count
+ * to stabilize. If a writer is active when we begin, we will fail the
+ * read_seqcount_retry() instead of stabilizing at the beginning of the
+ * critical section.
+ */
+static inline unsigned raw_seqcount_begin(const seqcount_t *s)
+{
+	unsigned ret = ACCESS_ONCE(s->sequence);
+	smp_rmb();
+	return ret & ~1;
+}
+
+/**
  * __read_seqcount_retry - end a seq-read critical section (without barrier)
  * @s: pointer to seqcount_t
  * @start: count, from read_seqcount_begin