Re: [PATCH 1/2] taskstats: set version in TGID exit notifications

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 30 Mar 2026 03:00:40 +0800 Yiyang Chen <cyyzero16@gmail.com> wrote:

> delay accounting started populating taskstats records with a valid
> version field via fill_pid() and fill_tgid().
> 
> Later, commit ad4ecbcba728 ("[PATCH] delay accounting taskstats
> interface send tgid once") changed the TGID exit path to send the
> cached signal->stats aggregate directly instead of building the outgoing
> record through fill_tgid(). Unlike fill_tgid(), fill_tgid_exit() only
> accumulates accounting data and never initializes stats->version.
> 
> As a result, TGID exit notifications can reach userspace with
> version == 0 even though PID exit notifications and
> TASKSTATS_CMD_GET replies carry a valid taskstats version.
> 
> Set stats->version = TASKSTATS_VERSION after copying the cached TGID
> aggregate into the outgoing netlink payload so all taskstats records are
> self-describing again.
> 
> Fixes: ad4ecbcba728 ("[PATCH] delay accounting taskstats interface send tgid once")

Thanks, lol, 20 years ago.

Can you explain how others can trigger this?  Some combination of
steps which results in the bad output?

> Cc: stable@vger.kernel.org

Is there a chance of breaking existing userspace here?  Some existing
userspace code which is expecting 0 here and will get surprised by this
change?

> --- a/kernel/taskstats.c
> +++ b/kernel/taskstats.c
> @@ -649,6 +649,7 @@ void taskstats_exit(struct task_struct *tsk, int group_dead)
>  		goto err;
>  
>  	memcpy(stats, tsk->signal->stats, sizeof(*stats));
> +	stats->version = TASKSTATS_VERSION;
>  
>  send:
>  	send_cpu_listeners(rep_skb, listeners);