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 96EDDC433EF for ; Fri, 25 Mar 2022 01:30:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1357337AbiCYBcN (ORCPT ); Thu, 24 Mar 2022 21:32:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33782 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355594AbiCYBb5 (ORCPT ); Thu, 24 Mar 2022 21:31:57 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 240CA3BBE7 for ; Thu, 24 Mar 2022 18:30:24 -0700 (PDT) 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 dfw.source.kernel.org (Postfix) with ESMTPS id B544C61949 for ; Fri, 25 Mar 2022 01:30:23 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 18C0FC340ED; Fri, 25 Mar 2022 01:30:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1648171823; bh=AjcxV+P5amPD4eWQGoKAFHikCghneRU5OaE4se0IAsg=; h=Date:To:From:Subject:From; b=ntyrJd41hmp+C+qkKK/qysB5TO0uxEQYa9cZoYAl6xHea9XSJxVtBwLurvF3ilCWe 2kCMq/qaShLsIO069prOX/hNhJr+FGN7kDLDvimklwRFJ4w42V1Y3LJNkovWihf9h4 j7+AHwqTf7FXYM/tzgVwwKOmTY7jcdzNgAGvwLDw= Date: Thu, 24 Mar 2022 18:30:22 -0700 To: mm-commits@vger.kernel.org, vdavydov.dev@gmail.com, tglx@linutronix.de, shakeelb@google.com, peterz@infradead.org, oliver.sang@intel.com, mkoutny@suse.com, mhocko@suse.com, mhocko@kernel.org, longman@redhat.com, hannes@cmpxchg.org, guro@fb.com, bigeasy@linutronix.de, akpm@linux-foundation.org From: Andrew Morton Subject: [merged] mm-memcg-protect-per-cpu-counter-by-disabling-preemption-on-preempt_rt-where-needed.patch removed from -mm tree Message-Id: <20220325013023.18C0FC340ED@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The patch titled Subject: mm/memcg: protect per-CPU counter by disabling preemption on PREEMPT_RT where needed. has been removed from the -mm tree. Its filename was mm-memcg-protect-per-cpu-counter-by-disabling-preemption-on-preempt_rt-where-needed.patch This patch was dropped because it was merged into mainline or a subsystem tree ------------------------------------------------------ From: Sebastian Andrzej Siewior Subject: mm/memcg: protect per-CPU counter by disabling preemption on PREEMPT_RT where needed. The per-CPU counter are modified with the non-atomic modifier. The consistency is ensured by disabling interrupts for the update. On non PREEMPT_RT configuration this works because acquiring a spinlock_t typed lock with the _irq() suffix disables interrupts. On PREEMPT_RT configurations the RMW operation can be interrupted. Another problem is that mem_cgroup_swapout() expects to be invoked with disabled interrupts because the caller has to acquire a spinlock_t which is acquired with disabled interrupts. Since spinlock_t never disables interrupts on PREEMPT_RT the interrupts are never disabled at this point. The code is never called from in_irq() context on PREEMPT_RT therefore disabling preemption during the update is sufficient on PREEMPT_RT. The sections which explicitly disable interrupts can remain on PREEMPT_RT because the sections remain short and they don't involve sleeping locks (memcg_check_events() is doing nothing on PREEMPT_RT). Disable preemption during update of the per-CPU variables which do not explicitly disable interrupts. Link: https://lkml.kernel.org/r/20220226204144.1008339-4-bigeasy@linutronix.de Signed-off-by: Sebastian Andrzej Siewior Acked-by: Roman Gushchin Reviewed-by: Shakeel Butt Cc: kernel test robot Cc: Michal Hocko Cc: Michal Hocko Cc: Michal Koutný Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Vladimir Davydov Cc: Waiman Long Signed-off-by: Andrew Morton --- mm/memcontrol.c | 56 +++++++++++++++++++++++++++++++++++++++++++++- 1 file changed, 55 insertions(+), 1 deletion(-) --- a/mm/memcontrol.c~mm-memcg-protect-per-cpu-counter-by-disabling-preemption-on-preempt_rt-where-needed +++ a/mm/memcontrol.c @@ -629,6 +629,35 @@ static DEFINE_SPINLOCK(stats_flush_lock) static DEFINE_PER_CPU(unsigned int, stats_updates); static atomic_t stats_flush_threshold = ATOMIC_INIT(0); +/* + * Accessors to ensure that preemption is disabled on PREEMPT_RT because it can + * not rely on this as part of an acquired spinlock_t lock. These functions are + * never used in hardirq context on PREEMPT_RT and therefore disabling preemtion + * is sufficient. + */ +static void memcg_stats_lock(void) +{ +#ifdef CONFIG_PREEMPT_RT + preempt_disable(); +#else + VM_BUG_ON(!irqs_disabled()); +#endif +} + +static void __memcg_stats_lock(void) +{ +#ifdef CONFIG_PREEMPT_RT + preempt_disable(); +#endif +} + +static void memcg_stats_unlock(void) +{ +#ifdef CONFIG_PREEMPT_RT + preempt_enable(); +#endif +} + static inline void memcg_rstat_updated(struct mem_cgroup *memcg, int val) { unsigned int x; @@ -705,6 +734,27 @@ void __mod_memcg_lruvec_state(struct lru pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); memcg = pn->memcg; + /* + * The caller from rmap relay on disabled preemption becase they never + * update their counter from in-interrupt context. For these two + * counters we check that the update is never performed from an + * interrupt context while other caller need to have disabled interrupt. + */ + __memcg_stats_lock(); + if (IS_ENABLED(CONFIG_DEBUG_VM) && !IS_ENABLED(CONFIG_PREEMPT_RT)) { + switch (idx) { + case NR_ANON_MAPPED: + case NR_FILE_MAPPED: + case NR_ANON_THPS: + case NR_SHMEM_PMDMAPPED: + case NR_FILE_PMDMAPPED: + WARN_ON_ONCE(!in_task()); + break; + default: + WARN_ON_ONCE(!irqs_disabled()); + } + } + /* Update memcg */ __this_cpu_add(memcg->vmstats_percpu->state[idx], val); @@ -712,6 +762,7 @@ void __mod_memcg_lruvec_state(struct lru __this_cpu_add(pn->lruvec_stats_percpu->state[idx], val); memcg_rstat_updated(memcg, val); + memcg_stats_unlock(); } /** @@ -794,8 +845,10 @@ void __count_memcg_events(struct mem_cgr if (mem_cgroup_disabled()) return; + memcg_stats_lock(); __this_cpu_add(memcg->vmstats_percpu->events[idx], count); memcg_rstat_updated(memcg, count); + memcg_stats_unlock(); } static unsigned long memcg_events(struct mem_cgroup *memcg, int event) @@ -7154,8 +7207,9 @@ void mem_cgroup_swapout(struct page *pag * important here to have the interrupts disabled because it is the * only synchronisation we have for updating the per-CPU variables. */ - VM_BUG_ON(!irqs_disabled()); + memcg_stats_lock(); mem_cgroup_charge_statistics(memcg, -nr_entries); + memcg_stats_unlock(); memcg_check_events(memcg, page_to_nid(page)); css_put(&memcg->css); _ Patches currently in -mm which might be from bigeasy@linutronix.de are