linux-kernel - Re: [PATCH v2] do_wait: make PIDTYPE

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Date:   Tue, 9 Mar 2021 14:42:00 -0600
From:   Jim Newsome <jnewsome@...project.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Christian Brauner <christian@...uner.io>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] do_wait: make PIDTYPE_PID case O(1) instead of O(n)

On 3/9/21 11:15, Oleg Nesterov wrote:
> Jim,
>
> Thanks, the patch looks good to me. Yet I think you need to send V3 even
> if I personally do not care ;) Please consider ./scripts/checkpatch.pl,
> it reports all the coding-style problems I was going to mention.

Thanks! I'd thought clang-format with the included configuration would
be sufficient, but apparently not :)

> Both if's use "int retval", to me it would be better to declare this variable
> at the start of do_wait_pid(). But again, I won't insist this is up to you.
My usual inclination is to avoid uninitialized variables and prefer
putting them in tighter scopes. I don't think it's really much of an
issue in this relatively short function though; happy to go with the
prevailing style.
> I am wondering if something like
>
> 	static inline bool is_parent(struct task_struct *tsk, struct task_struct *p, int flags)
> 	{
> 		return	tsk == p || !(flags & __WNOTHREAD)) && same_thread_group(tsk, p);
> 	}
>
> makes any sense to make do_wait_pid() more clear... probably not.

Yeah, I lean slightly towards the extra level of indirection not being
worth the deduplication.

I made a couple other small changes as well:

* No need for do_wait_pid to take the parameter `tsk` since it's only
ever called with `current`

* With that change, the declaration of `tsk` in `do_wait` can be moved
into a tighter scope of where it's used in the loop.

v3: https://lkml.org/lkml/2021/3/9/1134