linux-kernel - Re: [PATCH net 1/4] umh: add exit routine for UMH process

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Date:   Sun, 6 Jan 2019 14:34:52 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     David Miller <davem@...emloft.net>
Cc:     Netdev <netdev@...r.kernel.org>, linux-kernel@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>, ast@...nel.org,
        mcgrof@...nel.org
Subject: Re: [PATCH net 1/4] umh: add exit routine for UMH process

On Sun, 6 Jan 2019 at 07:10, David Miller <davem@...emloft.net> wrote:
>
> From: Taehee Yoo <ap420073@...il.com>
> Date: Mon, 31 Dec 2018 01:31:43 +0900
>
> > +void exit_umh(struct task_struct *tsk)
> > +{
> > +     struct umh_info *info;
> > +     pid_t pid = tsk->pid;
> > +
> > +     mutex_lock(&umh_list_lock);
> > +     list_for_each_entry(info, &umh_list, list) {
>

Thank you for review!

> So this is probably too expensive of a cost for every process exit.
> The problem is that the cost will be taken even if the process is
> not a UMH.
>

Yes, I agree with you.

> I've taken my time to respond in hopes that I could come up with a
> good alternative to suggest, but so far I don't have any better ideas.
>
> I'll keep thinking about this some more, please let me know if you
> have any ideas.

Thanks a lot for spending time to think about better ideas!
How about adding a new PF_UMH flag for task_struct->flags to identify
UMH process?
By using this flag, the exit_umh() can avoid unnecessary lookups.

Thanks again.