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 C89D04322E5; Mon, 17 Aug 2026 14:52:27 +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=1786978349; cv=none; b=r/g3dDn8bjryAOTNG4iJXm7MRPXVPPDKMVpeeRiAGtPNxhDPvQUOISJfUx7NbXquxeItZGbuUjjSkBBaYLNAgHnOa3lsUD+pDt7DTgL2Q/dIFSBc+4G4tWiSqIOd2ciDublFQyGco772Zf+uUjOanmMQWUDDfYrnff13hZvgR04= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786978349; c=relaxed/simple; bh=95whq3g+FSAdjMEhF9Jj7NE0Z9ctim4EXXCN8vX9VV0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=BoXO4U0sCrfaVMCb/JsKZrnE9sDea/1r1B3cWLrNVBEJYiRDSkly8Q+5iiyEEAq7DBKYIBpcr7OTXUDKd43+wNe4PSm+cwTVkNJw1MyJ0TGNKmrtTnmhKPgFGafAX/sYdPVxA8oKfh2hFMQguga5g5enMrnjiv0rPlK+oxPn0IM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=S6iz34VL; 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="S6iz34VL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E82121F00A3A; Mon, 17 Aug 2026 14:52:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786978347; bh=jieccRNFcEPeEDx5KU9JGpVrUY4JYdoq/Eq/DjL9Fcs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=S6iz34VLDy5O/Lx/O/L3MIE5H6wDLW6vCd1EYjh6IfazFQrH9Thf+HYnbjQX+YOm2 JEc6a8A9+vcyOONlHGdh0bIViseodwssfOBvtFOqr+SBmd+Z50BkbTp0UB2jSTfj1L 0yFVnNrIrFIvmuatr0BVoEreYxSUlvZWTamZEP4U= 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 6.12 170/181] sched/psi: Shut down rtpoll_timer in psi_cgroup_free() Date: Mon, 17 Aug 2026 15:34:24 +0200 Message-ID: <20260817132542.372528347@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260817132535.394764707@linuxfoundation.org> References: <20260817132535.394764707@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 6.12-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 @@ -1130,6 +1130,12 @@ 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");