Re: [PATCHSET v2] sched/psi: Fix psimon fork deadlock and rtpoll_timer UAF

[Tejun Heo]

On Sun, Jul 12, 2026 at 07:46:17AM -1000, Tejun Heo wrote:
> Hello,
> 
> v2: - Retagged sched/psi (was cgroup) (patch 1).
>     - Added a fix for a pre-existing rtpoll_timer use-after-free that the
>       Sashiko AI review flagged on the previous posting (patch 2).
> 
> v1: https://lore.kernel.org/r/20260710134945-psimon-fix-tj@xxxxxxxxxx
> 
> a5b98009f16d ("sched/psi: fix race between file release and pressure
> write") made pressure_write() fork the psimon kthread while holding
> cgroup_mutex, which deadlocks against the sched_ext enable path blocking
> forks before grabbing cgroup_mutex. Patch 1 moves the fork outside
> cgroup_mutex. Patch 2 fixes the use-after-free from a schedule attempt
> re-arming group->rtpoll_timer behind psi_trigger_destroy() by shutting
> down the timer when the group is freed.
> 
> Matt, patch 1 is unchanged from the previous posting except for the
> subject prefix, so test results against that posting still apply.
> 
> Peter, once these are reviewed and tested, how do you want them routed?
> I can take them through the cgroup tree if that works for you.

Applying this to cgroup/for-7.2-fixes. Please holler for any objections.

Thanks.

-- 
tejun