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 ot be more explicit about that.
Signed-off-by: Nikolay Borisov <nbori...@suse.com>
---
fs/btrfs/volumes.h | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h
index c5dd48eb7b3d..0b8ddcbf8462 100644
--- a/fs/btrfs/volumes.h
+++ b/fs/btrfs/volumes.h
@@ -520,7 +520,13 @@ 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;
}
--
2.7.4
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