sched/psi: Shut down rtpoll_timer in psi_cgroup_free()

Summary

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.

Timeline

1. Aug 22, 2026, 3:31 PM UTCCVE published
2. Oct 16, 2026, 7:01 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Oct 16, 2026, 7:05 PM UTCRecord last updated

Affected versions

• Linux Linux

  From 6bfcb6178925b1fd28c102e53d403091b8f49396 · fixed in 4addb102154b7cf6e2310ccbe20c3c08619e520d; From 8f91efd870ea5d8bc10b0fcc9740db51cd4c0c83 · fixed in 894a9300d7fb2e2951da92e565ae6de7ddfb0a69; From 8f91efd870ea5d8bc10b0fcc9740db51cd4c0c83 · fixed in 1e5ca82eee59caca6988f9d6e859786aab8a5fa0; From 8f91efd870ea5d8bc10b0fcc9740db51cd4c0c83 · fixed in 310b5a537a78c358a4cd244bd767c1a517a05459; From 8f91efd870ea5d8bc10b0fcc9740db51cd4c0c83 · fixed in 806fcff98c1d7cb3c1dc0015e55ebdbe819e6b08; From 8f91efd870ea5d8bc10b0fcc9740db51cd4c0c83 · fixed in 8037c5b2b2a447df52542f4d8535895d837bdcbd; From 8f91efd870ea5d8bc10b0fcc9740db51cd4c0c83 · fixed in 611e7821c4f83a671455658797336faecc3a5196; From 8f91efd870ea5d8bc10b0fcc9740db51cd4c0c83 · fixed in 5457025fa8ca3c0d2732109513de839e3e797190; From 5.10.50 · fixed in 5.10.266; From 5.12.17 · fixed in 5.13; From 5.13.2 · fixed in 5.14

• Linux Linux

  5.14

• KernelLinux

  fixed in 5.10.266; From 5.11.0 · fixed in 5.15.217; From 5.14.0 · fixed in 6.1.183; From 5.16.0 · fixed in 6.6.152; From 6.2.0 · fixed in 6.12.104; From 6.7.0 · fixed in 6.18.45; From 6.13.0 · fixed in 7.1.9

References 8