On 26.11.18 г. 11:07 ч., Anand Jain wrote:
> The fs_info::device_list_mutex and fs_info::scrub_lock creates a
> nested locks in btrfs_scrub_dev(). During the lock acquire the
> hierarchy is fs_info::device_list_mutex and then fs_info::scrub_lock,
> so following the same reverse order during unlock, that is
> fs_info::scrub_lock and then fs_info::device_list_mutex.
>
> Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
> ---
> fs/btrfs/scrub.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
> index 902819d3cf41..b1c2d1cdbd4b 100644
> --- a/fs/btrfs/scrub.c
> +++ b/fs/btrfs/scrub.c
> @@ -3865,7 +3865,6 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
> }
> sctx->readonly = readonly;
> dev->scrub_ctx = sctx;
> - mutex_unlock(&fs_info->fs_devices->device_list_mutex);
>
> /*
> * checking @scrub_pause_req here, we can avoid
> @@ -3875,15 +3874,14 @@ int btrfs_scrub_dev(struct btrfs_fs_info *fs_info, u64 devid, u64 start,
> atomic_inc(&fs_info->scrubs_running);
> mutex_unlock(&fs_info->scrub_lock);
>
> - if (!is_dev_replace) {
> - /*
> - * by holding device list mutex, we can
> - * kick off writing super in log tree sync.
> - */
> - mutex_lock(&fs_info->fs_devices->device_list_mutex);
> + /*
> + * by holding device list mutex, we can kick off writing super in log
> + * tree sync.
> + */
> + if (!is_dev_replace)
> ret = scrub_supers(sctx, dev);
> - mutex_unlock(&fs_info->fs_devices->device_list_mutex);
> - }
> +
> + mutex_unlock(&fs_info->fs_devices->device_list_mutex);
Have you considered whether this change will have any negative impact
due to the fact that __scrtub_blocked_if_needed can go to sleep for
arbitrary time with device_list_mutex held now ?
>
> if (!ret)
> ret = scrub_enumerate_chunks(sctx, dev, start, end);
>
