[v1] fs/proc: do_task_stat: use __for_each_thread()

[PATCH 5.15] fs/proc: do_task_stat: use __for_each_thread()

Posted by Heyne, Maximilian 6 months, 2 weeks ago

From: Oleg Nesterov <oleg@redhat.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@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Stable-dep-of: 7601df8031fd ("fs/proc: do_task_stat: use sig->stats_lock to gather the threads/children stats")
[mheyne: adjusted context]
Signed-off-by: Maximilian Heyne <mheyne@amazon.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.

---
 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 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);
+			}
 			rcu_read_unlock();
 		}
 	} while (need_seqretry(&sig->stats_lock, seq));
-- 
2.47.1




Amazon Web Services Development Center Germany GmbH
Tamara-Danz-Str. 13
10243 Berlin
Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
Sitz: Berlin
Ust-ID: DE 365 538 597

Re: [PATCH 5.15] fs/proc: do_task_stat: use __for_each_thread()

Posted by Harshit Mogalapalli 5 months, 1 week ago

Hi,

+ stable

On 05/06/25 19:37, Heyne, Maximilian wrote:
> From: Oleg Nesterov <oleg@redhat.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@redhat.com>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Signed-off-by: Andrew Morton <akpm@linux-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@amazon.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
> 
> 
> 
> 
> Amazon Web Services Development Center Germany GmbH
> Tamara-Danz-Str. 13
> 10243 Berlin
> Geschaeftsfuehrung: Christian Schlaeger, Jonathan Weiss
> Eingetragen am Amtsgericht Charlottenburg unter HRB 257764 B
> Sitz: Berlin
> Ust-ID: DE 365 538 597
> 
>

Re: [PATCH 5.15] fs/proc: do_task_stat: use __for_each_thread()

Posted by Greg KH 5 months, 1 week ago

On Wed, Jul 09, 2025 at 05:33:39PM +0530, Harshit Mogalapalli wrote:
> Hi,
> 
> + stable

Not much we can do with this, it needs to be submitted to us in a form
we can apply it in (i.e. sent to the stable list...)

thanks,

greg k-h