linux-kernel - Re: [RESEND PATCH 5.10] fs/proc: do_task_stat: use __for_each

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Message-ID: <2025071044-bunt-sister-9d9e@gregkh>
Date: Thu, 10 Jul 2025 15:09:20 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: "Heyne, Maximilian" <mheyne@...zon.de>
Cc: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	"Sauerwein, David" <dssauerw@...zon.de>,
	Sasha Levin <sashal@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [RESEND PATCH 5.10] fs/proc: do_task_stat: use
 __for_each_thread()

On Thu, Jul 10, 2025 at 12:35:43PM +0000, Heyne, Maximilian wrote:
> From: Oleg Nesterov <oleg@...hat.com>
> 
> [ Upstream commit 7904e53ed5a20fc678c01d5d1b07ec486425bb6a ]
> 
> do/while_each_thread should be avoided when possible.
> 
> Link: https://lkml.kernel.org/r/20230909164501.GA11581@redhat.com
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> Cc: Eric W. Biederman <ebiederm@...ssion.com>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Stable-dep-of: 7601df8031fd ("fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats")
> Cc: stable@...r.kernel.org
> [mheyne: adjusted context]
> Signed-off-by: Maximilian Heyne <mheyne@...zon.de>
> ---
> 
> Compile-tested only.
> We're seeing soft lock-ups with 5.10.237 because of the backport of
> commit 4fe85bdaabd6 ("fs/proc: do_task_stat: use sig->stats_lock to
> gather the threads/children stats").

And this fixes it?

How?

> 
> ---
>  fs/proc/array.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/proc/array.c b/fs/proc/array.c
> index 8fba6d39e776..77b94c04e4af 100644
> --- a/fs/proc/array.c
> +++ b/fs/proc/array.c
> @@ -512,18 +512,18 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
>  		cgtime = sig->cgtime;
>  
>  		if (whole) {
> -			struct task_struct *t = task;
> +			struct task_struct *t;
>  
>  			min_flt = sig->min_flt;
>  			maj_flt = sig->maj_flt;
>  			gtime = sig->gtime;
>  
>  			rcu_read_lock();
> -			do {
> +			__for_each_thread(sig, t) {
>  				min_flt += t->min_flt;
>  				maj_flt += t->maj_flt;
>  				gtime += task_gtime(t);
> -			} while_each_thread(task, t);
> +			}

Ideally, the code generated here should be identical as before, so why
is this change needed?

confused,

greg k-h