From 4660c49f9b4ad50eab410de09eeacc2e3aebf1f5 Mon Sep 17 00:00:00 2001 From: Nikolay Borisov <nborisov@suse.com> Date: Fri, 20 Oct 2017 18:10:58 +0300 Subject: [PATCH] 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> --- 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 38fd368ddfe74..177814a7c7584 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; } -- 2.30.2