Re: [PATCH 1/3] cgroup/rstat: Fix forceidle time in cpu.stat

[chenridong <chenridong@huawei.com>]

On 2025/1/24 1:47, Abel Wu wrote:
> The commit b824766504e4 ("cgroup/rstat: add force idle show helper")
> retrieves forceidle_time outside cgroup_rstat_lock for non-root cgroups
> which can be potentially inconsistent with other stats.
> 
> Rather than reverting that commit, fix it in a way that retains the
> effort of cleaning up the ifdef-messes.
> 
> Fixes: b824766504e4 ("cgroup/rstat: add force idle show helper")
> Signed-off-by: Abel Wu <wuyun.abel@bytedance.com>
> ---
>  kernel/cgroup/rstat.c | 29 +++++++++++++----------------
>  1 file changed, 13 insertions(+), 16 deletions(-)
> 
> diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c
> index 5877974ece92..c2784c317cdd 100644
> --- a/kernel/cgroup/rstat.c
> +++ b/kernel/cgroup/rstat.c
> @@ -613,36 +613,33 @@ static void cgroup_force_idle_show(struct seq_file *seq, struct cgroup_base_stat
>  void cgroup_base_stat_cputime_show(struct seq_file *seq)
>  {
>  	struct cgroup *cgrp = seq_css(seq)->cgroup;
> -	u64 usage, utime, stime, ntime;
> +	struct cgroup_base_stat bstat;
>  
>  	if (cgroup_parent(cgrp)) {
>  		cgroup_rstat_flush_hold(cgrp);
> -		usage = cgrp->bstat.cputime.sum_exec_runtime;
> +		bstat = cgrp->bstat;

Thank you for finding that.
In my version 2, I used to assign cgrp->bstat to bstat.
This is Tj's comment:
https://lore.kernel.org/linux-kernel/ZoQ2ti7nnz9EJSc3@slm.duckdns.org/

Best regards,
Ridong

>  		cputime_adjust(&cgrp->bstat.cputime, &cgrp->prev_cputime,
> -			       &utime, &stime);
> -		ntime = cgrp->bstat.ntime;
> +			       &bstat.cputime.utime, &bstat.cputime.stime);
>  		cgroup_rstat_flush_release(cgrp);
>  	} else {
> -		/* cgrp->bstat of root is not actually used, reuse it */
> -		root_cgroup_cputime(&cgrp->bstat);
> -		usage = cgrp->bstat.cputime.sum_exec_runtime;
> -		utime = cgrp->bstat.cputime.utime;
> -		stime = cgrp->bstat.cputime.stime;
> -		ntime = cgrp->bstat.ntime;
> +		root_cgroup_cputime(&bstat);
>  	}
>  
> -	do_div(usage, NSEC_PER_USEC);
> -	do_div(utime, NSEC_PER_USEC);
> -	do_div(stime, NSEC_PER_USEC);
> -	do_div(ntime, NSEC_PER_USEC);
> +	do_div(bstat.cputime.sum_exec_runtime, NSEC_PER_USEC);
> +	do_div(bstat.cputime.utime, NSEC_PER_USEC);
> +	do_div(bstat.cputime.stime, NSEC_PER_USEC);
> +	do_div(bstat.ntime, NSEC_PER_USEC);
>  
>  	seq_printf(seq, "usage_usec %llu\n"
>  			"user_usec %llu\n"
>  			"system_usec %llu\n"
>  			"nice_usec %llu\n",
> -			usage, utime, stime, ntime);
> +			bstat.cputime.sum_exec_runtime,
> +			bstat.cputime.utime,
> +			bstat.cputime.stime,
> +			bstat.ntime);
>  
> -	cgroup_force_idle_show(seq, &cgrp->bstat);
> +	cgroup_force_idle_show(seq, &bstat);
>  }
>  
>  /* Add bpf kfuncs for cgroup_rstat_updated() and cgroup_rstat_flush() */