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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>
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@ -519,7 +519,13 @@ static inline int btrfs_dev_stat_read_and_reset(struct btrfs_device *dev,
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int ret;
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ret = atomic_xchg(dev->dev_stat_values + index, 0);
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smp_mb__before_atomic();
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/*
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* atomic_xchg implies a full memory barriers as per atomic_t.txt:
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* - RMW operations that have a return value are fully ordered;
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*
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* This implicit memory barriers is paired with the smp_rmb in
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* btrfs_run_dev_stats
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*/
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atomic_inc(&dev->dev_stats_ccnt);
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return ret;
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}
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