From mboxrd@z Thu Jan 1 00:00:00 1970 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 5925CE77347 for ; Fri, 29 Sep 2023 22:30:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233862AbjI2WaJ (ORCPT ); Fri, 29 Sep 2023 18:30:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51746 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229508AbjI2WaG (ORCPT ); Fri, 29 Sep 2023 18:30:06 -0400 Received: from mail-wm1-x32c.google.com (mail-wm1-x32c.google.com [IPv6:2a00:1450:4864:20::32c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0CC98F1 for ; Fri, 29 Sep 2023 15:30:05 -0700 (PDT) Received: by mail-wm1-x32c.google.com with SMTP id 5b1f17b1804b1-406650da82bso1602505e9.3 for ; Fri, 29 Sep 2023 15:30:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1696026603; x=1696631403; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=J4ODyI/xGDfBDr3VSCKLFMfeRUTcBjJWMeC4Qx7RcLU=; b=ceYZ/TRYjzLJMUz9TiOyb16DwNx7ybYKb1RzxSlCxtYlM5LLHg5AFVcRxF1sQKfW6R PvJPxTxvA9x2uMb8vY3a3Gj/2t7/H+opZwDi41Hlb4zmxc7ydobYuy2V0G3r3F4zW1yI j98hv5ZDA6BE1a0FhVbdOwxZEWd85AIXufTrlkVy2FU11ER0nn3AknFSPeWD7V69wK9Z zNBMfgIcTMnbw4qX+SS/QWxbmFedBRAkiheCZVOojUuywWC4oLYL+rKetg9SH85E/9zR 3ZCtUQBKwtDRqQ8FvqbBBRwftf40X8CoVfPlPI/zk0l3xXNfMKNsDWngolHWTfzxN4Mg rTaw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1696026603; x=1696631403; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=J4ODyI/xGDfBDr3VSCKLFMfeRUTcBjJWMeC4Qx7RcLU=; b=WFkU+upjcgH4DvcBKeWoFzaAsq1r21upIuiVOeb0LmlPaYS7RF8ml//mHIevWQTWtO /AoxBq8a0+egWgR/VN9OVCjER/SOQR/RRL53i50rsor54zsauFGx+CZGz/JKDzhKjdWK jVrGl5lXavtgRAUovAyjbcYY5slZBM7hd+QKP3QjYyOjVNd+jeSCfqw0CjorVYqFKCQ/ zt85WqOa/epjB1nusUzB4BMDwDaBL+wxJx26LjwWOd7CrAP/euzEWce8b5bEJ5qLh7ju gubzRMuxqDlCgr0l8qB36M+Qy54cuc2u3MeC9xH0NlOMDv6lokFf9gheH4ozCVHO/U4v 2F0w== X-Gm-Message-State: AOJu0YwclrOD81mX1Egi2bunbaTxlnpXRSMg++Cg8G3wQGzkFIaqkeSK zjUpgYCYj3EtdlG0D0JPI/g= X-Google-Smtp-Source: AGHT+IHMqmbjL3PpGXeDkwNFoF00EDu0jzJQkz1KBQVWnHJGrsmsq8HADGwhMX77DgL3YjXJ+VnqBw== X-Received: by 2002:adf:ea49:0:b0:320:485:7010 with SMTP id j9-20020adfea49000000b0032004857010mr4620006wrn.67.1696026603166; Fri, 29 Sep 2023 15:30:03 -0700 (PDT) Received: from localhost ([2a00:23c5:dc8c:8701:1663:9a35:5a7b:1d76]) by smtp.gmail.com with ESMTPSA id b4-20020adfee84000000b003197c7d08ddsm1555572wro.71.2023.09.29.15.30.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 29 Sep 2023 15:30:02 -0700 (PDT) Date: Fri, 29 Sep 2023 23:30:01 +0100 From: Lorenzo Stoakes To: "Liam R. Howlett" Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jann Horn , Vlastimil Babka , Suren Baghdasaryan , Matthew Wilcox Subject: Re: [PATCH v3 3/3] mmap: Add clarifying comment to vma_merge() code Message-ID: <1c7c1869-ef9c-487f-9c8e-08a51d9f8efe@lucifer.local> References: <20230929183041.2835469-1-Liam.Howlett@oracle.com> <20230929183041.2835469-4-Liam.Howlett@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230929183041.2835469-4-Liam.Howlett@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 29, 2023 at 02:30:41PM -0400, Liam R. Howlett wrote: > When tracing through the code in vma_merge(), it was not completely > clear why the error return to a dup_anon_vma() call would not overwrite > a previous attempt to the same function. This commit adds a comment > specifying why it is safe. > > Suggested-by: Jann Horn > Link: https://lore.kernel.org/linux-mm/CAG48ez3iDwFPR=Ed1BfrNuyUJPMK_=StjxhUsCkL6po1s7bONg@mail.gmail.com/ > Signed-off-by: Liam R. Howlett > --- > mm/mmap.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index f9f0a5fe4db4..9967acbd070f 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -943,6 +943,11 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm, > vma_start_write(curr); > remove = curr; > remove2 = next; > + /* > + * Note that the dup_anon_vma below cannot overwrite err > + * since the first caller would do nothing unless next > + * has an anon_vma. > + */ > if (!next->anon_vma) > err = dup_anon_vma(prev, curr, &anon_dup); > } > -- > 2.40.1 > Nice comment! It causes me to sick up a bit in my mouth that this is a thing, but it's good to have it documented. Reviewed-by: Lorenzo Stoakes