linux-kernel - Re: [PATCH 09/10] kthread: Ensure struct kthread is present for all kthreads

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Date:   Sat, 08 Jan 2022 12:20:53 -0600
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexey Gladkov <legion@...nel.org>,
        Kyle Huey <me@...ehuey.com>, Oleg Nesterov <oleg@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [PATCH 09/10] kthread: Ensure struct kthread is present for all
 kthreads

Al Viro <viro@...iv.linux.org.uk> writes:

> On Wed, Dec 08, 2021 at 02:25:31PM -0600, Eric W. Biederman wrote:
>> Today the rules are a bit iffy and arbitrary about which kernel
>> threads have struct kthread present.  Both idle threads and thread
>> started with create_kthread want struct kthread present so that is
>> effectively all kernel threads.  Make the rule that if PF_KTHREAD
>> and the task is running then struct kthread is present.
>> 
>> This will allow the kernel thread code to using tsk->exit_code
>> with different semantics from ordinary processes.
>
> Getting rid of ->exit_code abuse is independent from this.
> I'm not saying that this change is a bad idea, but it's an
> independent thing.  Simply turn these two failure exits
> into do_exit(0) in 06/10 and that's it.  Then this one
> would get rid of if (!self) and the second of those two
> calls, but it won't be nailed to that point of queue.

That is a good point.

As this code has been in linux-next for a while, I am going to leave
the dependency in place in the interests of sending Linus tested code.

This change with the bit about which field points to struct kthread
seems like a good idea on it's own merits.

Eric