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| author |   Nikolay Borisov <nborisov@suse.com> | 2017-10-20 18:10:58 +0300 |
|---|---|---|
| committer |   David Sterba <dsterba@suse.com> | 2018-01-22 16:08:10 +0100 |
| commit | 4660c49f9b4ad50eab410de09eeacc2e3aebf1f5 (patch) | |
| tree | 89130cb6eb02df2822a16dc5debd7c432fe781e2 /fs/btrfs/volumes.h | |
| parent | btrfs: Fix memory barriers usage with device stats counters (diff) | |
| download | linux-dev-4660c49f9b4ad50eab410de09eeacc2e3aebf1f5.tar.xz linux-dev-4660c49f9b4ad50eab410de09eeacc2e3aebf1f5.zip | |
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>
Diffstat (limited to 'fs/btrfs/volumes.h')
| -rw-r--r-- | fs/btrfs/volumes.h | 8 |
1 files changed, 7 insertions, 1 deletions
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h index 38fd368ddfe7..177814a7c758 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; } |