From nobody Mon Jun 29 21:04:20 2026 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 96F32C433F5 for ; Wed, 2 Feb 2022 15:17:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345423AbiBBPRm (ORCPT ); Wed, 2 Feb 2022 10:17:42 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53318 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229758AbiBBPRl (ORCPT ); Wed, 2 Feb 2022 10:17:41 -0500 Received: from mail-qt1-x830.google.com (mail-qt1-x830.google.com [IPv6:2607:f8b0:4864:20::830]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 95731C061714 for ; Wed, 2 Feb 2022 07:17:41 -0800 (PST) Received: by mail-qt1-x830.google.com with SMTP id h8so11544071qtk.13 for ; Wed, 02 Feb 2022 07:17:41 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=2Yzp7UgTJSpEim5DDLkluETjGLodKmNBRS1tOayIgzo=; b=dUggYVyRuCJbR+LNUU3wymi7BuY6ux8cpsuX3sFjZAEJAJ9LgcZVAi4KRvqwD07KTW /0VDx7zMtrHKomHN/b1SMVppGZfqqJ1VGzrHzOkYdXEqaY497YiokOuVRNHHEVSsWbI2 2LB1KixG3pwmdcVGMbXhN84Q1sEyUq9g1eJtWQmFPeJ1DK7yPFSUdp1nlFmLWf3BtzA0 1//LqNK6kJ1W3WBIv2WN2/obvaZ5LpR8kzlcCMb/jQiRxzbSv1LLBaqp1kc6EbT2mJXa MTMYH1wg7PDWs/AgHIzV1BCNFKtnfqpg91GLM515VCJ5lLXR2En2zl80z/mAAgjOEOt+ uvJg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=2Yzp7UgTJSpEim5DDLkluETjGLodKmNBRS1tOayIgzo=; b=XBWQ4Ov6BmUAhohfUEOWgXQONlr8/zqDGcqoUYP9ACzPSHBAgR5HzIdtzHwS0ltV5N V43WbAzdUfrphAqhQDDK6fAJsztZjo3moeavEEvaWTDijYSGj+hJ3ofrq/xLZCGu0poI 5E67SVJufzi3eySs5SukNFeF9U03Yw/5AxRdbs36L52VPEOwrK8daeTeIRsz3P2VDhts ysHGZXMJMfgUnJevPyOwvBigY8gefUEm87NMefFWNPZ7omA4Ht2toaAJDSA7I+NOzeLo IC3ZDmbBIn7oMdDtRkwr7iVNxIdn9nuzca/jgtJI0HQ5h3KhEHB7ta13pDO9BTIi0Es+ oqfA== X-Gm-Message-State: AOAM5309lTbFakA4ggQzcx1c+e3afRiywSUAlgmIkdXD+ZMvwhJTPztZ OGo4YqXzR8UBK5q7yJpIcjjnm37aVeg= X-Google-Smtp-Source: ABdhPJxS9wfrjBuLVX0099xeKce/X18D6wukaXuk37UojkekhRKJ73nx5hUopPBtysTDOGyF/prI6A== X-Received: by 2002:a05:622a:492:: with SMTP id p18mr20473063qtx.56.1643815060423; Wed, 02 Feb 2022 07:17:40 -0800 (PST) Received: from pm2-ws13.praxislan02.com ([2001:470:8:67e:ba27:ebff:fee8:ce27]) by smtp.gmail.com with ESMTPSA id bi5sm5667607qkb.116.2022.02.02.07.17.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Feb 2022 07:17:39 -0800 (PST) From: Jason Andryuk To: linux-kernel@vger.kernel.org Cc: "Eric W . Biederman" , Cyrill Gorcunov , Jason Andryuk Subject: [PATCH] kcmp: Comment get_file_raw_ptr() RCU usage Date: Wed, 2 Feb 2022 10:17:34 -0500 Message-Id: <20220202151734.10418-1-jandryuk@gmail.com> X-Mailer: git-send-email 2.34.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" This usage of RCU appears wrong since the pointer is passed outside the RCU region. However, it is not dereferenced, so it is "okay". Leave a comment for the next reader. Without a reference, these comparisons are racy, but even with their use inside an RCU region, the result could go stale. Signed-off-by: Jason Andryuk --- I was looking for examples of task_lookup_fd_rcu()/files_lookup_fd_rcu() and found this. It differed from the example given in Documentation/filesystems/files.rst, so I was initially confused. A comment seemed appropriate to avoid confusion. kernel/kcmp.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/kcmp.c b/kernel/kcmp.c index 5353edfad8e1..4fb23f242e0f 100644 --- a/kernel/kcmp.c +++ b/kernel/kcmp.c @@ -63,6 +63,9 @@ get_file_raw_ptr(struct task_struct *task, unsigned int i= dx) { struct file *file; =20 + /* This RCU locking is only present to silence warnings. The pointer + * value is only used for comparison and not dereferenced, so it is + * acceptable. */ rcu_read_lock(); file =3D task_lookup_fd_rcu(task, idx); rcu_read_unlock(); --=20 2.34.1