linux-kernel - Re: [PATCH 5.15] fs/proc: do_task_stat: use __for_each

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Message-ID: <ef0e0364-29e2-47c2-8f0a-93f385cebf08@oracle.com>
Date: Wed, 9 Jul 2025 17:33:39 +0530
From: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
To: "Heyne, Maximilian" <mheyne@...zon.de>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Cc: Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman"
 <ebiederm@...ssion.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "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: [PATCH 5.15] fs/proc: do_task_stat: use __for_each_thread()

Hi,

+ stable

On 05/06/25 19:37, 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=ather the threads/children stats")
> [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"). I'm assuming this is broken on 5.15
> too.
> 

Note: We saw this as well after backporting the above mentioned commit 
from 5.15.y and your backport resolves it for us as well on 5.15.y based 
branch.


Thanks,
Harshit
> ---
>   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 2cb01aaa67187..2ff568dc58387 100644
> --- a/fs/proc/array.c
> +++ b/fs/proc/array.c
> @@ -530,18 +530,18 @@ static int do_task_stat(struct seq_file *m, struct pi=_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);
> +			}
>   			rcu_read_unlock();
>   		}
>   	} while (need_seqretry(&sig->stats_lock, seq));
> -- =2.47.1
> 
> 
> 
> 
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