btrfs: Remove redundant memory barrier in dev stats
As per atomic_t.txt documentation :
- RMW operations that have a return value are fully ordered;
atomic_xchg is one such operation so it already includes everything it
needs w.r.t memory ordering and add a comment to be more explicit about
that.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index 38fd368..177814a 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -519,7 +519,13 @@ static inline int btrfs_dev_stat_read_and_reset(struct btrfs_device *dev,
int ret;
ret = atomic_xchg(dev->dev_stat_values + index, 0);
- smp_mb__before_atomic();
+ /*
+ * atomic_xchg implies a full memory barriers as per atomic_t.txt:
+ * - RMW operations that have a return value are fully ordered;
+ *
+ * This implicit memory barriers is paired with the smp_rmb in
+ * btrfs_run_dev_stats
+ */
atomic_inc(&dev->dev_stats_ccnt);
return ret;
}
