From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 42C0D3F0ABE; Mon, 17 Aug 2026 13:49:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786974600; cv=none; b=NarJHBULersvsxPoSBImZzvs+w878wAQNPcOVhLbysoU4SKPD9M7keAVPYU8WC397UvDfMLUxDKMiVlPJfZr0x+yWi7ZOi02WvBXOz2VwDeLDi235XwLyAWOOQATmDGVJtN8XI+5Huq0InKKjxBGrcyJ6fyD+1GgQCgV3Xb+c0c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786974600; c=relaxed/simple; bh=59En/gqm/nR3NkxGTo5bB62+w910bnezEUkBW9Fq0fI=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=SjmCG0M0Vh1kIbsf0u8KDnpLe2zOhfWr+//deimos79k35sNwEbZhjPdlGFNcda3sqWxLY4cRbbKBZW7dPLJ7PiJBNFOx0gS4Xga4wlwxNE7V2aj4yiNhGgNz3Q2VDFNkI98I5FJjbNmZMON9/z+o5v+W0dEX8HF966YByeko9Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=PmquYhXu; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="PmquYhXu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 269E81F00A3A; Mon, 17 Aug 2026 13:49:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786974588; bh=Hc73pzHaNhKn39FptiJzK30CjKkFLZurYu86qUTNwYU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=PmquYhXu85JPgMeGdiARSX1XqLsqBE5bMe8hzMOOm8BkXRGzI0qtGEe1zChNTFCrE VvnRVPUBFVZAuYnx2ATw7fKhkPJSl1QAGtkB8t7+gRG5YkmViqa+r7wiJtKK1x8i8S Ggjy7e+QZo83LI8a0XYLmTJYkpm7IuuywFfMBNHI= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Sashiko AI , Tejun Heo , Johannes Weiner , Matt Fleming , Suren Baghdasaryan Subject: [PATCH 7.1 258/271] sched/psi: Shut down rtpoll_timer in psi_cgroup_free() Date: Mon, 17 Aug 2026 15:33:03 +0200 Message-ID: <20260817132547.349821613@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260817132536.752504388@linuxfoundation.org> References: <20260817132536.752504388@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 7.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tejun Heo commit 5457025fa8ca3c0d2732109513de839e3e797190 upstream. 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. Fixes: 8f91efd870ea ("psi: Fix race between psi_trigger_create/destroy") Cc: stable@vger.kernel.org # v5.10+ Reported-by: Sashiko AI Closes: https://lore.kernel.org/all/20260711000434.36C4A1F000E9@smtp.kernel.org/ Signed-off-by: Tejun Heo Acked-by: Johannes Weiner Tested-by: Matt Fleming Acked-by: Suren Baghdasaryan Signed-off-by: Greg Kroah-Hartman --- kernel/sched/psi.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/kernel/sched/psi.c +++ b/kernel/sched/psi.c @@ -1134,6 +1134,12 @@ void psi_cgroup_free(struct cgroup *cgro return; cancel_delayed_work_sync(&cgroup->psi->avgs_work); + /* + * A psi_schedule_rtpoll_work() call racing the last trigger's + * destruction may have re-armed the timer after psi_trigger_destroy() + * deleted it. Spurious firing while the group is alive is harmless. + */ + timer_shutdown_sync(&cgroup->psi->rtpoll_timer); free_percpu(cgroup->psi->pcpu); /* All triggers must be removed by now */ WARN_ONCE(cgroup->psi->rtpoll_states, "psi: trigger leak\n");