CVE-2026-74594sched/psi: Shut down rtpoll_timer in psi_cgroup_free()

Official description

In the Linux kernel, the following vulnerability has been resolved: sched/psi: Shut down rtpoll_timer in psi_cgroup_free() psi_schedule_rtpoll_work() is called locklessly from the scheduler hotpath and can race psi_trigger_destroy() taking down the last rtpoll trigger under rtpoll_trigger_lock: psi_schedule_rtpoll_work() psi_trigger_destroy() rcu_read_lock(); task = rcu_dereference(rtpoll_task); rcu_assign_pointer(rtpoll_task, NULL); timer_delete(&rtpoll_timer); mod_timer(&rtpoll_timer, ...); rcu_read_unlock(); synchronize_rcu(); kthread_stop(task_to_destroy); The group can then be freed with the re-armed timer still pending, and poll_timer_fn() runs on freed memory. 461daba06bdc ("psi: eliminate kthread_worker from psi trigger scheduling mechanism") deleted the timer synchronously after the synchronize_rcu(), which prevented this but raced trigger creation instead: the deletion could cancel the timer that a new trigger set armed during the grace period and, as creation also reinitialized the timer at the time, corrupt it. 8f91efd870ea ("psi: Fix race between psi_trigger_create/destroy") moved the initialization into group_init() and the deletion into the locked section, trading the creation races for the window above. Neither placement in the destruction path works. A pending timer firing while the group is alive is harmless though. poll_timer_fn() just wakes the rtpoll waitqueue and doesn't re-arm itself. Bind the timer to the group's lifetime instead and shut it down in psi_cgroup_free(). Nothing can arm it by then. timer_shutdown_sync() because the timer is never armed again.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/4addb102154b7cf6e2310ccbe20c3c08619e520d
• https://git.kernel.org/stable/c/894a9300d7fb2e2951da92e565ae6de7ddfb0a69
• https://git.kernel.org/stable/c/1e5ca82eee59caca6988f9d6e859786aab8a5fa0
• https://git.kernel.org/stable/c/310b5a537a78c358a4cd244bd767c1a517a05459
• https://git.kernel.org/stable/c/806fcff98c1d7cb3c1dc0015e55ebdbe819e6b08
• https://git.kernel.org/stable/c/8037c5b2b2a447df52542f4d8535895d837bdcbd
• https://git.kernel.org/stable/c/611e7821c4f83a671455658797336faecc3a5196
• https://git.kernel.org/stable/c/5457025fa8ca3c0d2732109513de839e3e797190