Merge branch 'for-3.5/dt2' of git://git.kernel.org/pub/scm/linux/kernel/git/swarren...

[firefly-linux-kernel-4.4.55.git] / include / linux / seqlock.h

diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index c6db9fb33c448f28197ffb6d135689daf58625b6..600060e25ec6cb644fd4141f48e2493490305c8a 100644 (file)
--- 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;
@@ -165,6 +165,27 @@ static inline unsigned read_seqcount_begin(const seqcount_t *s)
        return ret;
 }
 
+/**
+ * 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