From patchwork Fri Feb 11 22:35:36 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Sebastian Andrzej Siewior X-Patchwork-Id: 12744027 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6FA20C433EF for ; Fri, 11 Feb 2022 22:35:56 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BF1AA6B007E; Fri, 11 Feb 2022 17:35:49 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7EBFE8D0002; Fri, 11 Feb 2022 17:35:49 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 52EB46B007D; Fri, 11 Feb 2022 17:35:49 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0121.hostedemail.com [216.40.44.121]) by kanga.kvack.org (Postfix) with ESMTP id 30DF16B007D for ; Fri, 11 Feb 2022 17:35:49 -0500 (EST) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E17B99A7EE for ; Fri, 11 Feb 2022 22:35:48 +0000 (UTC) X-FDA: 79131957576.19.BEA913C Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by imf06.hostedemail.com (Postfix) with ESMTP id 4909218000B for ; Fri, 11 Feb 2022 22:35:48 +0000 (UTC) From: Sebastian Andrzej Siewior DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1644618946; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HNmdg+JhjUejtOXXg+4Fk6i3cxKj6CVFrDw059VuYAw=; b=46dq9VzbbmdqZ70qFsNWfZ5g1qSqckcMO5u9CQwNIJ57NbiSFXd5JsQ4Itaeg29JgbpsX2 hoDhM4uSa3yy5IaoO93TSrLKi3VE/G14Gs5tBC5CAvbDl+rS+DVi+38+QO/mRJVxIeBzkE /F0ALzclpTURjEH42SdcEl/USdQvJ0w2yPix9xC/V2WnpJdKc6ihZVmhaJFI+oIZJ9VuMD 8bETxQV2JHLJVn6sUNc6qB96M4J9O6NSCnXFsOl0TiX7g6l17U83IuLq+IUgIsZhkk7/1P +9/FbP1+GxZKpWhBonR0PXrGsbGuFhnV2Tj91ufxGAiXnzKRuQcukuKDldgqng== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1644618946; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=HNmdg+JhjUejtOXXg+4Fk6i3cxKj6CVFrDw059VuYAw=; b=ACG3ifFELAPCRkKD198JMrBMfCDTNClKoFl4B13unbdZ2sZZvxnPZr5M+Ah2tR6+ChW8ht gQVjDQIJqkYxbqBw== To: cgroups@vger.kernel.org, linux-mm@kvack.org Cc: Andrew Morton , Johannes Weiner , Michal Hocko , =?utf-8?q?Michal_Koutn=C3=BD?= , Peter Zijlstra , Thomas Gleixner , Vladimir Davydov , Waiman Long , Sebastian Andrzej Siewior Subject: [PATCH v2 3/4] mm/memcg: Protect per-CPU counter by disabling preemption on PREEMPT_RT where needed. Date: Fri, 11 Feb 2022 23:35:36 +0100 Message-Id: <20220211223537.2175879-4-bigeasy@linutronix.de> In-Reply-To: <20220211223537.2175879-1-bigeasy@linutronix.de> References: <20220211223537.2175879-1-bigeasy@linutronix.de> MIME-Version: 1.0 X-Rspamd-Queue-Id: 4909218000B X-Stat-Signature: kwd7ng64nfnrrmz6bhurr36opbmu7rjn X-Rspam-User: Authentication-Results: imf06.hostedemail.com; dkim=pass header.d=linutronix.de header.s=2020 header.b=46dq9Vzb; dkim=pass header.d=linutronix.de header.s=2020e header.b=ACG3ifFE; spf=pass (imf06.hostedemail.com: domain of bigeasy@linutronix.de designates 193.142.43.55 as permitted sender) smtp.mailfrom=bigeasy@linutronix.de; dmarc=pass (policy=none) header.from=linutronix.de X-Rspamd-Server: rspam06 X-HE-Tag: 1644618948-355678 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: 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 Acked-by: Roman Gushchin after incorporating Johannes's --- mm/memcontrol.c | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index c1caa662946dc..466466f285cea 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -705,6 +705,8 @@ 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); @@ -712,6 +714,8 @@ 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(); } /** @@ -794,8 +798,12 @@ 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) @@ -7148,9 +7156,18 @@ 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, -nr_entries); + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) { + VM_BUG_ON(!irqs_disabled()); + mem_cgroup_charge_statistics(memcg, -nr_entries); + } else { + preempt_disable(); + mem_cgroup_charge_statistics(memcg, -nr_entries); + preempt_enable(); + } + memcg_check_events(memcg, page_to_nid(page)); css_put(&memcg->css);