From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9D761C3DA78 for ; Sun, 15 Jan 2023 14:30:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230462AbjAOOaq (ORCPT ); Sun, 15 Jan 2023 09:30:46 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39316 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230368AbjAOOap (ORCPT ); Sun, 15 Jan 2023 09:30:45 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 85FB2B76A for ; Sun, 15 Jan 2023 06:30:44 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 29AD5B80B02 for ; Sun, 15 Jan 2023 14:30:43 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 36086C433D2; Sun, 15 Jan 2023 14:30:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1673793041; bh=jz2iSieTb8JBdbEYFks2XD80f4G3ApXGiO5yVq+npZM=; h=Subject:To:Cc:From:Date:From; b=2MLv/nEJOAYCtGzLLjUOjX/2YlzjNcIaJVSJ+9Jvvq+1xSZXHOyQN1MrWOeWkODBl MIEyfLqPfsjUTWsgjD6vKnaSiDCpjSlrwK7pFbI/hUFOgEriNX1X/Dcvg8KYrkwHne aJFWWfTR6un0ocX5LHHnliX8rSFJ+7RIBH3P8Ex4= Subject: FAILED: patch "[PATCH] x86/resctrl: Fix task CLOSID/RMID update race" failed to apply to 5.10-stable tree To: peternewman@google.com, babu.moger@amd.com, bp@alien8.de, reinette.chatre@intel.com, stable@kernel.org Cc: From: Date: Sun, 15 Jan 2023 15:30:33 +0100 Message-ID: <167379303346150@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . Possible dependencies: fe1f0714385f ("x86/resctrl: Fix task CLOSID/RMID update race") e0ad6dc8969f ("x86/resctrl: Use task_curr() instead of task_struct->on_cpu to prevent unnecessary IPI") ae28d1aae48a ("x86/resctrl: Use an IPI instead of task_work_add() to update PQR_ASSOC MSR") thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From fe1f0714385fbcf76b0cbceb02b7277d842014fc Mon Sep 17 00:00:00 2001 From: Peter Newman Date: Tue, 20 Dec 2022 17:11:23 +0100 Subject: [PATCH] x86/resctrl: Fix task CLOSID/RMID update race When the user moves a running task to a new rdtgroup using the task's file interface or by deleting its rdtgroup, the resulting change in CLOSID/RMID must be immediately propagated to the PQR_ASSOC MSR on the task(s) CPUs. x86 allows reordering loads with prior stores, so if the task starts running between a task_curr() check that the CPU hoisted before the stores in the CLOSID/RMID update then it can start running with the old CLOSID/RMID until it is switched again because __rdtgroup_move_task() failed to determine that it needs to be interrupted to obtain the new CLOSID/RMID. Refer to the diagram below: CPU 0 CPU 1 ----- ----- __rdtgroup_move_task(): curr <- t1->cpu->rq->curr __schedule(): rq->curr <- t1 resctrl_sched_in(): t1->{closid,rmid} -> {1,1} t1->{closid,rmid} <- {2,2} if (curr == t1) // false IPI(t1->cpu) A similar race impacts rdt_move_group_tasks(), which updates tasks in a deleted rdtgroup. In both cases, use smp_mb() to order the task_struct::{closid,rmid} stores before the loads in task_curr(). In particular, in the rdt_move_group_tasks() case, simply execute an smp_mb() on every iteration with a matching task. It is possible to use a single smp_mb() in rdt_move_group_tasks(), but this would require two passes and a means of remembering which task_structs were updated in the first loop. However, benchmarking results below showed too little performance impact in the simple approach to justify implementing the two-pass approach. Times below were collected using `perf stat` to measure the time to remove a group containing a 1600-task, parallel workload. CPU: Intel(R) Xeon(R) Platinum P-8136 CPU @ 2.00GHz (112 threads) # mkdir /sys/fs/resctrl/test # echo $$ > /sys/fs/resctrl/test/tasks # perf bench sched messaging -g 40 -l 100000 task-clock time ranges collected using: # perf stat rmdir /sys/fs/resctrl/test Baseline: 1.54 - 1.60 ms smp_mb() every matching task: 1.57 - 1.67 ms [ bp: Massage commit message. ] Fixes: ae28d1aae48a ("x86/resctrl: Use an IPI instead of task_work_add() to update PQR_ASSOC MSR") Fixes: 0efc89be9471 ("x86/intel_rdt: Update task closid immediately on CPU in rmdir and unmount") Signed-off-by: Peter Newman Signed-off-by: Borislav Petkov (AMD) Reviewed-by: Reinette Chatre Reviewed-by: Babu Moger Cc: Link: https://lore.kernel.org/r/20221220161123.432120-1-peternewman@google.com diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c index e5a48f05e787..5993da21d822 100644 --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c @@ -580,8 +580,10 @@ static int __rdtgroup_move_task(struct task_struct *tsk, /* * Ensure the task's closid and rmid are written before determining if * the task is current that will decide if it will be interrupted. + * This pairs with the full barrier between the rq->curr update and + * resctrl_sched_in() during context switch. */ - barrier(); + smp_mb(); /* * By now, the task's closid and rmid are set. If the task is current @@ -2401,6 +2403,14 @@ static void rdt_move_group_tasks(struct rdtgroup *from, struct rdtgroup *to, WRITE_ONCE(t->closid, to->closid); WRITE_ONCE(t->rmid, to->mon.rmid); + /* + * Order the closid/rmid stores above before the loads + * in task_curr(). This pairs with the full barrier + * between the rq->curr update and resctrl_sched_in() + * during context switch. + */ + smp_mb(); + /* * If the task is on a CPU, set the CPU in the mask. * The detection is inaccurate as tasks might move or