From patchwork Tue Jul 12 11:22:36 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Oberhollenzer X-Patchwork-Id: 589992 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 9CD59CCA481 for ; Tue, 12 Jul 2022 11:46:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231206AbiGLLqQ (ORCPT ); Tue, 12 Jul 2022 07:46:16 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58476 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231770AbiGLLqN (ORCPT ); Tue, 12 Jul 2022 07:46:13 -0400 Received: from mail.infraroot.at (mail.infraroot.at [IPv6:2001:41d0:701:1100::afc]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AD382B197F for ; Tue, 12 Jul 2022 04:46:10 -0700 (PDT) Received: from localtoast.corp.sigma-star.at (unknown [82.150.214.1]) by mail.infraroot.at (Postfix) with ESMTPSA id DA1F9409FD; Tue, 12 Jul 2022 13:22:47 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 mail.infraroot.at DA1F9409FD DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=infraroot.at; s=default; t=1657624968; bh=E9i38R1wm0EM8ywtxezt7+nBR0GmxMlEPh/7Wks4NTU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Ottv+2dge/7N/OV3xX7uJ8ytaNlCQSuOJ1/GZBT3kNdZ+8ucbKs7ci24ZE7GC1l2A 26jLZDsOFJRFiwhx5hz1QOqxGd1s5R3jobsjuwZaNR8Nz9iDNCKjTPpGFbrthfgpRE zCf79rq41egyKymd1ONDd+76OFsliq3cHl84eN/g= From: David Oberhollenzer To: linux-rt-users@vger.kernel.org Cc: williams@redhat.com, bigeasy@linutronix.de, richard@nod.at, David Oberhollenzer Subject: [PATCH 2/4] mm/memcg: Protect per-CPU counter by disabling preemption on PREEMPT_RT where needed. Date: Tue, 12 Jul 2022 13:22:36 +0200 Message-Id: <20220712112238.18824-3-goliath@infraroot.at> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220712112238.18824-1-goliath@infraroot.at> References: <20220712112238.18824-1-goliath@infraroot.at> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-rt-users@vger.kernel.org From: Sebastian Andrzej Siewior 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. Signed-off-by: Sebastian Andrzej Siewior [do: backported to v5.15] Signed-off-by: David Oberhollenzer --- mm/memcontrol.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 31fcc702ca33..c2e1aed2e1fb 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -683,6 +683,8 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, pn = container_of(lruvec, struct mem_cgroup_per_node, lruvec); memcg = pn->memcg; + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_disable(); /* Update memcg */ __this_cpu_add(memcg->vmstats_percpu->state[idx], val); @@ -690,6 +692,8 @@ void __mod_memcg_lruvec_state(struct lruvec *lruvec, enum node_stat_item idx, __this_cpu_add(pn->lruvec_stats_percpu->state[idx], val); memcg_rstat_updated(memcg, val); + if (IS_ENABLED(CONFIG_PREEMPT_RT)) + preempt_enable(); } /** @@ -790,8 +794,12 @@ void __count_memcg_events(struct mem_cgroup *memcg, enum vm_event_item idx, if (mem_cgroup_disabled()) return; + if (IS_ENABLED(PREEMPT_RT)) + preempt_disable(); __this_cpu_add(memcg->vmstats_percpu->events[idx], count); memcg_rstat_updated(memcg, count); + if (IS_ENABLED(PREEMPT_RT)) + preempt_enable(); } static unsigned long memcg_events(struct mem_cgroup *memcg, int event) @@ -7243,9 +7251,18 @@ void mem_cgroup_swapout(struct page *page, swp_entry_t entry) * i_pages lock which is taken with interrupts-off. It is * important here to have the interrupts disabled because it is the * only synchronisation we have for updating the per-CPU variables. + * On PREEMPT_RT interrupts are never disabled and the updates to per-CPU + * variables are synchronised by keeping preemption disabled. */ - VM_BUG_ON(!irqs_disabled()); - mem_cgroup_charge_statistics(memcg, page, -nr_entries); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { + VM_BUG_ON(!irqs_disabled()); + mem_cgroup_charge_statistics(memcg, page, -nr_entries); + } else { + preempt_disable(); + mem_cgroup_charge_statistics(memcg, page, -nr_entries); + preempt_enable(); + } + memcg_check_events(memcg, page_to_nid(page)); css_put(&memcg->css);