linux-kernel - Re: [PATCH] kill do_each

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Message-ID: <20230818081617.GA5339@redhat.com>
Date:   Fri, 18 Aug 2023 10:16:17 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Christian Brauner <brauner@...nel.org>,
        Kees Cook <keescook@...omium.org>, linux-ia64@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kill do_each_thread()

On 08/18, Jiri Slaby wrote:
>
> On 17. 08. 23, 18:37, Oleg Nesterov wrote:
> >Eric has pointed out that we still have 3 users of do_each_thread().
> >Change them to use for_each_process_thread() and kill this helper.
>
> Is there any change in behavior?

No.

Well, there is a subtle change, after do_each_thread/while_each_thread
g == t == &init_task, while after for_each_process_thread() they both
point to nowhere, but this doesn't matter.

> Why is for_each_process_thread() better than do_each_thread()?

Say, for_each_process_thread() is rcu safe, do_each_thread() is not.

And certainly

	for_each_process_thread(p, t) {
		do_something(p, t);
	}

looks better than

	do_each_thread(p, t) {
		do_something(p, t);
	} while_each_thread(p, t);

And again, there are only 3 users of this awkward helper left.
It should have been killed years ago and in fact I thought it
had already been killed. It uses while_each_thread() which needs
some changes.

Oleg.