[PATCH v3] blk-cgroup: Replace u64 sync with spinlock for iostat update

[tj at kernel.org]

Hello,

On Wed, Jul 17, 2024 at 02:18:39PM -0400, Waiman Long wrote:
> Well, it can be confusing whether we are dealing with blkg->iostat or
> blkg->iostat_cpu. In many cases, we are dealing with iostat_cpu instead of
> iostat like __blkcg_rstat_flush() and blkg_clear_stat(). So we can't
> eliminate the use of u64_stats_update_begin_irqsave() in those cases.

I mean, we need to distinguish them. For 32bits, blkg->iostat has multiple
updaters, so we can't use u64_sync; however, blkg->iostat_cpu has only one
updater (except blkg_clear_stat() which I don't think we need to worry too
much about), so u64_sync is fine.

Thanks.

-- 
tejun