Re: [PATCH] kernel/sys: do not use tasklist_lock to set/get scheduling priorities

[Peter Zijlstra]

On Fri, May 01, 2020 at 08:05:39PM -0700, Davidlohr Bueso wrote:
> For both setpriority(2) and getpriority(2) there's really no need
> to be taking the tasklist_lock at all - for which both share it
> for the entirety of the syscall. The tasklist_lock does not protect
> reading/writing the p->static_prio and task lookups are already rcu
> safe, providing a stable pointer.

RCU-safe, as in, it will not crash.. However, without tasklist_lock the
thread iterations (for PRIO_PGRP/PRIO_USER) now race against fork().

That is a user observable change in behaviour.

Do we care about it? No idea, and your Changelog also doesn't provide
clue.