diff options
Diffstat (limited to 'fs/btrfs/volumes.c')
| -rw-r--r-- | fs/btrfs/volumes.c | 18 |
1 files changed, 16 insertions, 2 deletions
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c index 6879de3a16c4..6631f48c6a11 100644 --- a/fs/btrfs/volumes.c +++ b/fs/btrfs/volumes.c @@ -7093,10 +7093,24 @@ int btrfs_run_dev_stats(struct btrfs_trans_handle *trans, mutex_lock(&fs_devices->device_list_mutex); list_for_each_entry(device, &fs_devices->devices, dev_list) { - if (!device->dev_stats_valid || !btrfs_dev_stats_dirty(device)) + stats_cnt = atomic_read(&device->dev_stats_ccnt); + if (!device->dev_stats_valid || stats_cnt == 0) continue; - stats_cnt = atomic_read(&device->dev_stats_ccnt); + + /* + * There is a LOAD-LOAD control dependency between the value of + * dev_stats_ccnt and updating the on-disk values which requires + * reading the in-memory counters. Such control dependencies + * require explicit read memory barriers. + * + * This memory barriers pairs with smp_mb__before_atomic in + * btrfs_dev_stat_inc/btrfs_dev_stat_set and with the full + * barrier implied by atomic_xchg in + * btrfs_dev_stats_read_and_reset + */ + smp_rmb(); + ret = update_dev_stat_item(trans, fs_info, device); if (!ret) atomic_sub(stats_cnt, &device->dev_stats_ccnt); |