diff options
author | Nikolay Borisov <nborisov@suse.com> | 2017-10-24 13:47:37 +0300 |
---|---|---|
committer | David Sterba <dsterba@suse.com> | 2018-01-22 16:08:10 +0100 |
commit | 9deae9689231964972a94bb56a79b669f9d47ac1 (patch) | |
tree | 0bb88d586ee621e630216e5e5348c02bdd798a20 /fs/btrfs/volumes.h | |
parent | 1cb34c8ecd4623909c66bccb91ee7f6483e04441 (diff) |
btrfs: Fix memory barriers usage with device stats counters
Commit addc3fa74e5b ("Btrfs: Fix the problem that the dirty flag of dev
stats is cleared") reworked the way device stats changes are tracked. A
new atomic dev_stats_ccnt counter was introduced which is incremented
every time any of the device stats counters are changed. This serves as
a flag whether there are any pending stats changes. However, this patch
only partially implemented the correct memory barriers necessary:
- It only ordered the stores to the counters but not the reads e.g.
btrfs_run_dev_stats
- It completely omitted any comments documenting the intended design and
how the memory barriers pair with each-other
This patch provides the necessary comments as well as adds a missing
smp_rmb in btrfs_run_dev_stats. Furthermore since dev_stats_cnt is only
a snapshot at best there was no point in reading the counter twice -
once in btrfs_dev_stats_dirty and then again when assigning stats_cnt.
Just collapse both reads into 1.
Fixes: addc3fa74e5b ("Btrfs: Fix the problem that the dirty flag of dev stats is cleared")
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.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 | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/fs/btrfs/volumes.h b/fs/btrfs/volumes.h index bf0d53a96b4a..38fd368ddfe7 100644 --- a/fs/btrfs/volumes.h +++ b/fs/btrfs/volumes.h @@ -497,6 +497,12 @@ static inline void btrfs_dev_stat_inc(struct btrfs_device *dev, int index) { atomic_inc(dev->dev_stat_values + index); + /* + * This memory barrier orders stores updating statistics before stores + * updating dev_stats_ccnt. + * + * It pairs with smp_rmb() in btrfs_run_dev_stats(). + */ smp_mb__before_atomic(); atomic_inc(&dev->dev_stats_ccnt); } @@ -522,6 +528,12 @@ static inline void btrfs_dev_stat_set(struct btrfs_device *dev, int index, unsigned long val) { atomic_set(dev->dev_stat_values + index, val); + /* + * This memory barrier orders stores updating statistics before stores + * updating dev_stats_ccnt. + * + * It pairs with smp_rmb() in btrfs_run_dev_stats(). + */ smp_mb__before_atomic(); atomic_inc(&dev->dev_stats_ccnt); } |