From patchwork Wed Dec 1 20:41:05 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Tom Zanussi X-Patchwork-Id: 520069 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 20899C433F5 for ; Wed, 1 Dec 2021 20:42:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353079AbhLAUpe (ORCPT ); Wed, 1 Dec 2021 15:45:34 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47778 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1352960AbhLAUol (ORCPT ); Wed, 1 Dec 2021 15:44:41 -0500 Received: from sin.source.kernel.org (sin.source.kernel.org [IPv6:2604:1380:40e1:4800::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A16B3C061761; Wed, 1 Dec 2021 12:41:19 -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 sin.source.kernel.org (Postfix) with ESMTPS id EDD95CE1DED; Wed, 1 Dec 2021 20:41:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 438DBC53FCC; Wed, 1 Dec 2021 20:41:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1638391276; bh=ie+rHXtHrUJO2uja2y5OVbalZjaKsOdco+591qQQ0S8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:In-Reply-To: References:From; b=GeagFzHAEGIA9MICMldYqzaFOreDKNBShKyUzXkdCqpuc5Il8y2wJw1OE74GwTxsB P2YYCYA1ZyFm7rxEa6avS4kATXKvnNVciOVHp1Y6FZy2O3lFhmuUgj++QYiiA4bPg2 l0YEjWweNLIB6tgZPJDH4cq8DTRUh2ST/0zDvTRUwnCaPjh7jKR/6HRY+fYCiIxduC eHXEEsqN2fTVTlnJ9xdQQs2mbobLBX0Rqc+/DwCpXFVUM2WXinPer3VQIkqhJjwjm5 +75q4OYHqRQWuz1WHGF6XeuWCN4Tezwhg+RaD1mtUCoa+HPdTHBsveeQn1cxxaJfA5 I6noGTxL3V9pA== From: zanussi@kernel.org To: LKML , linux-rt-users , Steven Rostedt , Thomas Gleixner , Carsten Emde , John Kacur , Sebastian Andrzej Siewior , Daniel Wagner , Clark Williams , "Luis Claudio R. Goncalves" , Tom Zanussi Cc: stable-rt@vger.kernel.org Subject: [PATCH RT 5/8] fscache: Use only one fscache_object_cong_wait. Date: Wed, 1 Dec 2021 14:41:05 -0600 Message-Id: X-Mailer: git-send-email 2.17.1 In-Reply-To: References: In-Reply-To: References: Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org From: Sebastian Andrzej Siewior v5.4.161-rt67-rc1 stable review patch. If anyone has any objections, please let me know. ----------- [ Upstream commit 74920695ab51a6d180dcd6554193cc8427758360 ] In the commit mentioned below, fscache was converted from slow-work to workqueue. slow_work_enqueue() and slow_work_sleep_till_thread_needed() did not use a per-CPU workqueue. They choose from two global waitqueues depending on the SLOW_WORK_VERY_SLOW bit which was not set so it always one waitqueue. I can't find out how it is ensured that a waiter on certain CPU is woken up be the other side. My guess is that the timeout in schedule_timeout() ensures that it does not wait forever (or a random wake up). fscache_object_sleep_till_congested() must be invoked from preemptible context in order for schedule() to work. In this case this_cpu_ptr() should complain with CONFIG_DEBUG_PREEMPT enabled except the thread is bound to one CPU. wake_up() wakes only one waiter and I'm not sure if it is guaranteed that only one waiter exists. Replace the per-CPU waitqueue with one global waitqueue. Fixes: 8b8edefa2fffb ("fscache: convert object to use workqueue instead of slow-work") Reported-by: Gregor Beck Cc: stable-rt@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Tom Zanussi --- fs/fscache/internal.h | 1 - fs/fscache/main.c | 6 ------ fs/fscache/object.c | 11 +++++------ 3 files changed, 5 insertions(+), 13 deletions(-) diff --git a/fs/fscache/internal.h b/fs/fscache/internal.h index d09d4e69c818..b557eb2263d2 100644 --- a/fs/fscache/internal.h +++ b/fs/fscache/internal.h @@ -95,7 +95,6 @@ extern unsigned fscache_debug; extern struct kobject *fscache_root; extern struct workqueue_struct *fscache_object_wq; extern struct workqueue_struct *fscache_op_wq; -DECLARE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait); extern unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n); diff --git a/fs/fscache/main.c b/fs/fscache/main.c index e1f1083b61a5..00367233ef8a 100644 --- a/fs/fscache/main.c +++ b/fs/fscache/main.c @@ -41,8 +41,6 @@ struct kobject *fscache_root; struct workqueue_struct *fscache_object_wq; struct workqueue_struct *fscache_op_wq; -DEFINE_PER_CPU(wait_queue_head_t, fscache_object_cong_wait); - /* these values serve as lower bounds, will be adjusted in fscache_init() */ static unsigned fscache_object_max_active = 4; static unsigned fscache_op_max_active = 2; @@ -139,7 +137,6 @@ unsigned int fscache_hash(unsigned int salt, unsigned int *data, unsigned int n) static int __init fscache_init(void) { unsigned int nr_cpus = num_possible_cpus(); - unsigned int cpu; int ret; fscache_object_max_active = @@ -162,9 +159,6 @@ static int __init fscache_init(void) if (!fscache_op_wq) goto error_op_wq; - for_each_possible_cpu(cpu) - init_waitqueue_head(&per_cpu(fscache_object_cong_wait, cpu)); - ret = fscache_proc_init(); if (ret < 0) goto error_proc; diff --git a/fs/fscache/object.c b/fs/fscache/object.c index cfeba839a0f2..c93860274f2f 100644 --- a/fs/fscache/object.c +++ b/fs/fscache/object.c @@ -807,6 +807,8 @@ void fscache_object_destroy(struct fscache_object *object) } EXPORT_SYMBOL(fscache_object_destroy); +static DECLARE_WAIT_QUEUE_HEAD(fscache_object_cong_wait); + /* * enqueue an object for metadata-type processing */ @@ -815,12 +817,10 @@ void fscache_enqueue_object(struct fscache_object *object) _enter("{OBJ%x}", object->debug_id); if (fscache_get_object(object, fscache_obj_get_queue) >= 0) { - wait_queue_head_t *cong_wq = - &get_cpu_var(fscache_object_cong_wait); if (queue_work(fscache_object_wq, &object->work)) { if (fscache_object_congested()) - wake_up(cong_wq); + wake_up(&fscache_object_cong_wait); } else fscache_put_object(object, fscache_obj_put_queue); @@ -842,16 +842,15 @@ void fscache_enqueue_object(struct fscache_object *object) */ bool fscache_object_sleep_till_congested(signed long *timeoutp) { - wait_queue_head_t *cong_wq = this_cpu_ptr(&fscache_object_cong_wait); DEFINE_WAIT(wait); if (fscache_object_congested()) return true; - add_wait_queue_exclusive(cong_wq, &wait); + add_wait_queue_exclusive(&fscache_object_cong_wait, &wait); if (!fscache_object_congested()) *timeoutp = schedule_timeout(*timeoutp); - finish_wait(cong_wq, &wait); + finish_wait(&fscache_object_cong_wait, &wait); return fscache_object_congested(); }