From patchwork Thu Mar 16 01:41:22 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Vernet X-Patchwork-Id: 13176913 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 56AE5C7618B for ; Thu, 16 Mar 2023 01:41:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229892AbjCPBlm (ORCPT ); Wed, 15 Mar 2023 21:41:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229844AbjCPBlk (ORCPT ); Wed, 15 Mar 2023 21:41:40 -0400 Received: from mail-qt1-f172.google.com (mail-qt1-f172.google.com [209.85.160.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CDACEB860D; Wed, 15 Mar 2023 18:41:32 -0700 (PDT) Received: by mail-qt1-f172.google.com with SMTP id l13so285742qtv.3; Wed, 15 Mar 2023 18:41:32 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1678930891; 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=fujln5B4PJVc7FU0F2EjRjzV5VR7c7BJfqwtEXGQG30=; b=fb9D9hLFXdrVtLcdhi5BPw8DzBQmDCcbu0PPRLD8eaUxDGZWBoM91Zo+X0RZwpvNLr C+X+iunwZu0DpWRzI0RA+HEs/zLlC3Lup/YbmPrvZcul1kNsxbBNp63dbgG3+bTM5vPD kGhOzsH7inIQVwfp2N+slHi4yuPVUV2wtlELX9nMPLHJg+Bh1Pmh0aJvU64TsE1nAxE0 4LdDajy9Z9fCSkRQBWawFIMPGmWJzSytUtSP1t/vYJtCsZ4WQS0HIWB4Is7KCQLr4Gwm w5ssmj2KcymOhS1PzRE4uu1LrWXhSnEAQLd1v93m9Jmg7AT68beEEhDPKz9JmTuuwRZb O/+w== X-Gm-Message-State: AO0yUKXj/PXGh556SY4JB384n7SbCHTJesYkQkTMSWGWlLiQp4s4gRUb 6qxvylzL1sHtchtcCOuGjKawAiCRqahB4d62 X-Google-Smtp-Source: AK7set+RdTtIsY3zUnM14bUgfPDAx7kJsfU9mIvCdawhkU7qZ5kCOSCscrFjSTCMTRrTrAhMFE/28Q== X-Received: by 2002:a05:622a:174c:b0:3bf:d0c7:12df with SMTP id l12-20020a05622a174c00b003bfd0c712dfmr3506016qtk.63.1678930891324; Wed, 15 Mar 2023 18:41:31 -0700 (PDT) Received: from localhost ([2620:10d:c091:400::5:5c58]) by smtp.gmail.com with ESMTPSA id x24-20020ac86b58000000b003bfa2c512e6sm4735074qts.20.2023.03.15.18.41.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Mar 2023 18:41:30 -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 5/5] bpf,docs: Remove bpf_cpumask_kptr_get() from documentation Date: Wed, 15 Mar 2023 20:41:22 -0500 Message-Id: <20230316014122.678082-6-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 Now that the kfunc no longer exists, we can remove it and instead describe how RCU can be used to get a struct bpf_cpumask from a map value. This patch updates the BPF documentation accordingly. Signed-off-by: David Vernet --- Documentation/bpf/cpumasks.rst | 30 ++++++++++-------------------- 1 file changed, 10 insertions(+), 20 deletions(-) diff --git a/Documentation/bpf/cpumasks.rst b/Documentation/bpf/cpumasks.rst index 75344cd230e5..41efd8874eeb 100644 --- a/Documentation/bpf/cpumasks.rst +++ b/Documentation/bpf/cpumasks.rst @@ -117,12 +117,7 @@ For example: As mentioned and illustrated above, these ``struct bpf_cpumask *`` objects can also be stored in a map and used as kptrs. If a ``struct bpf_cpumask *`` is in a map, the reference can be removed from the map with bpf_kptr_xchg(), or -opportunistically acquired with bpf_cpumask_kptr_get(): - -.. kernel-doc:: kernel/bpf/cpumask.c - :identifiers: bpf_cpumask_kptr_get - -Here is an example of a ``struct bpf_cpumask *`` being retrieved from a map: +opportunistically acquired using RCU: .. code-block:: c @@ -144,7 +139,7 @@ Here is an example of a ``struct bpf_cpumask *`` being retrieved from a map: /** * A simple example tracepoint program showing how a * struct bpf_cpumask * kptr that is stored in a map can - * be acquired using the bpf_cpumask_kptr_get() kfunc. + * be passed to kfuncs using RCU protection. */ SEC("tp_btf/cgroup_mkdir") int BPF_PROG(cgrp_ancestor_example, struct cgroup *cgrp, const char *path) @@ -158,26 +153,21 @@ Here is an example of a ``struct bpf_cpumask *`` being retrieved from a map: if (!v) return -ENOENT; + bpf_rcu_read_lock(); /* Acquire a reference to the bpf_cpumask * kptr that's already stored in the map. */ - kptr = bpf_cpumask_kptr_get(&v->cpumask); - if (!kptr) + kptr = v->cpumask; + if (!kptr) { /* If no bpf_cpumask was present in the map, it's because * we're racing with another CPU that removed it with * bpf_kptr_xchg() between the bpf_map_lookup_elem() - * above, and our call to bpf_cpumask_kptr_get(). - * bpf_cpumask_kptr_get() internally safely handles this - * race, and will return NULL if the cpumask is no longer - * present in the map by the time we invoke the kfunc. + * above, and our load of the pointer from the map. */ + bpf_rcu_read_unlock(); return -EBUSY; + } - /* Free the reference we just took above. Note that the - * original struct bpf_cpumask * kptr is still in the map. It will - * be freed either at a later time if another context deletes - * it from the map, or automatically by the BPF subsystem if - * it's still present when the map is destroyed. - */ - bpf_cpumask_release(kptr); + bpf_cpumask_setall(kptr); + bpf_rcu_read_unlock(); return 0; }