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

[Eric W. Biederman]

Al Viro <viro@xxxxxxxxxxxxxxxxxx> 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