From patchwork Thu Mar 16 01:41:18 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Vernet X-Patchwork-Id: 13176909 X-Patchwork-Delegate: bpf@iogearbox.net 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 C18FDC7618D for ; Thu, 16 Mar 2023 01:41:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229456AbjCPBl2 (ORCPT ); Wed, 15 Mar 2023 21:41:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57200 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229704AbjCPBl2 (ORCPT ); Wed, 15 Mar 2023 21:41:28 -0400 Received: from mail-qt1-f171.google.com (mail-qt1-f171.google.com [209.85.160.171]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2436BAB080; Wed, 15 Mar 2023 18:41:27 -0700 (PDT) Received: by mail-qt1-f171.google.com with SMTP id t9so267390qtx.8; Wed, 15 Mar 2023 18:41:27 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1678930886; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=RmYJO+iIXCovawotEcIt4TeAe1rA/wKRkg1b4WWjtqo=; b=k02aeUMyEIDSiaISUUew1Pm80Sr21sa1WkgpEnh8QfN6tmURi5iJJIAHnCyRU9nPy7 f32sLb5SNjPSiWJzTjnxGcgLecazi/YgI4jfCDFxZ9u48DChaXf4TDw1nfE2TrWoYFj/ GGiL+bmGOUQqotvIh0lnH6TGdFCCGm0OsjcS707t29zWCkq059CTMwiGmIqh9DitoGBK 3e6M6MxaT0NMdrUubnAoltd4YDf0Pk+uaJAmtxO0bl8ke2Vg2dxFW98zPLJr64gbhLQi 9IuFRZuYWFAsb7EVfGzNs4FGxBTDOEzNoMvcc3gj7ZH/gWq9TyAKXHLRfjPi9Y0GsdgZ wRIQ== X-Gm-Message-State: AO0yUKWMrfU0Rm9/m2cs7sdZX/nG6YfwVH1T/+3cceOeEgFhS5SO+1IO 4HVVi9W21uq2wsWRNZcU6dKRN9UN5941VYl/ X-Google-Smtp-Source: AK7set/tePkpx+xqSL3Fa44zFtsjJiZ1mY595ah/w/GGapXjUAczBIgrfnSHIPfdccQaAlsvhA4wiA== X-Received: by 2002:a05:622a:1449:b0:3b8:6c8e:4f85 with SMTP id v9-20020a05622a144900b003b86c8e4f85mr3085144qtx.43.1678930885853; Wed, 15 Mar 2023 18:41:25 -0700 (PDT) Received: from localhost ([2620:10d:c091:400::5:5c58]) by smtp.gmail.com with ESMTPSA id f33-20020a05622a1a2100b003bfb5fd72a7sm5048670qtb.86.2023.03.15.18.41.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Mar 2023 18:41:25 -0700 (PDT) From: David Vernet To: bpf@vger.kernel.org Cc: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, song@kernel.org, yhs@meta.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com Subject: [PATCH bpf-next 1/5] bpf: Free struct bpf_cpumask in call_rcu handler Date: Wed, 15 Mar 2023 20:41:18 -0500 Message-Id: <20230316014122.678082-2-void@manifault.com> X-Mailer: git-send-email 2.39.0 In-Reply-To: <20230316014122.678082-1-void@manifault.com> References: <20230316014122.678082-1-void@manifault.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org X-Patchwork-Delegate: bpf@iogearbox.net The struct bpf_cpumask type uses the bpf_mem_cache_{alloc,free}() APIs to allocate and free its cpumasks. The bpf_mem allocator may currently immediately reuse some memory when its freed, without waiting for an RCU read cycle to elapse. We want to be able to treat struct bpf_cpumask objects as completely RCU safe. This is necessary for two reasons: 1. bpf_cpumask_kptr_get() currently does an RCU-protected refcnt_inc_not_zero(). This of course assumes that the underlying memory is not reused, and is therefore unsafe in its current form. 2. We want to be able to get rid of bpf_cpumask_kptr_get() entirely, and intead use the superior kptr RCU semantics now afforded by the verifier. This patch fixes (1), and enables (2), by making struct bpf_cpumask RCU safe. A subsequent patch will update the verifier to allow struct bpf_cpumask * pointers to be passed to KF_RCU kfuncs, and then a latter patch will remove bpf_cpumask_kptr_get(). Fixes: 516f4d3397c9 ("bpf: Enable cpumasks to be queried and used as kptrs") Signed-off-by: David Vernet --- kernel/bpf/cpumask.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/cpumask.c b/kernel/bpf/cpumask.c index b6587ec40f1b..9ab462c5848a 100644 --- a/kernel/bpf/cpumask.c +++ b/kernel/bpf/cpumask.c @@ -24,6 +24,7 @@ */ struct bpf_cpumask { cpumask_t cpumask; + struct rcu_head rcu; refcount_t usage; }; @@ -108,6 +109,16 @@ __bpf_kfunc struct bpf_cpumask *bpf_cpumask_kptr_get(struct bpf_cpumask **cpumas return cpumask; } +static void cpumask_free_cb(struct rcu_head *head) +{ + struct bpf_cpumask *cpumask; + + cpumask = container_of(head, struct bpf_cpumask, rcu); + migrate_disable(); + bpf_mem_cache_free(&bpf_cpumask_ma, cpumask); + migrate_enable(); +} + /** * bpf_cpumask_release() - Release a previously acquired BPF cpumask. * @cpumask: The cpumask being released. @@ -121,11 +132,8 @@ __bpf_kfunc void bpf_cpumask_release(struct bpf_cpumask *cpumask) if (!cpumask) return; - if (refcount_dec_and_test(&cpumask->usage)) { - migrate_disable(); - bpf_mem_cache_free(&bpf_cpumask_ma, cpumask); - migrate_enable(); - } + if (refcount_dec_and_test(&cpumask->usage)) + call_rcu(&cpumask->rcu, cpumask_free_cb); } /**