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 X-Spam-Level: X-Spam-Status: No, score=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3FA4EC433E1 for ; Tue, 30 Jun 2020 14:14:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 1ED432072D for ; Tue, 30 Jun 2020 14:14:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388596AbgF3OOj (ORCPT ); Tue, 30 Jun 2020 10:14:39 -0400 Received: from smtprelay0085.hostedemail.com ([216.40.44.85]:48984 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727773AbgF3OOj (ORCPT ); Tue, 30 Jun 2020 10:14:39 -0400 Received: from filter.hostedemail.com (clb03-v110.bra.tucows.net [216.40.38.60]) by smtprelay07.hostedemail.com (Postfix) with ESMTP id 2E210181D3028; Tue, 30 Jun 2020 14:14:38 +0000 (UTC) X-Session-Marker: 6A6F6540706572636865732E636F6D X-HE-Tag: crown41_290f39a26e78 X-Filterd-Recvd-Size: 3023 Received: from XPS-9350.home (unknown [47.151.133.149]) (Authenticated sender: joe@perches.com) by omf14.hostedemail.com (Postfix) with ESMTPA; Tue, 30 Jun 2020 14:14:36 +0000 (UTC) Message-ID: Subject: Re: [PATCH] mm: util: update the kerneldoc for kstrdup_const() From: Joe Perches To: David Hildenbrand , Bartosz Golaszewski , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Bartosz Golaszewski Date: Tue, 30 Jun 2020 07:14:35 -0700 In-Reply-To: <98163576-c98e-77f7-17a7-efd04dc2e86f@redhat.com> References: <20200628152500.17916-1-brgl@bgdev.pl> <693db5a878ac09994e2a27c64cb14c0e552f3f50.camel@perches.com> <7f1439be-75c4-3a07-ab7b-f4505bf30c48@redhat.com> <644c67ae316bde28669f660aa5aade274d19a2d0.camel@perches.com> <98163576-c98e-77f7-17a7-efd04dc2e86f@redhat.com> Content-Type: text/plain; charset="ISO-8859-1" User-Agent: Evolution 3.36.2-0ubuntu1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2020-06-30 at 10:57 +0200, David Hildenbrand wrote: > On 29.06.20 21:21, Joe Perches wrote: > > On Mon, 2020-06-29 at 12:54 +0200, David Hildenbrand wrote: > > > On 28.06.20 19:37, Joe Perches wrote: > > > > On Sun, 2020-06-28 at 17:25 +0200, Bartosz Golaszewski wrote: > > > > > From: Bartosz Golaszewski > > > > > > > > > > Memory allocated with kstrdup_const() must not be passed to regular > > > > > krealloc() as it is not aware of the possibility of the chunk residing > > > > > in .rodata. Since there are no potential users of krealloc_const() > > > > > at the moment, let's just update the doc to make it explicit. > > > > > > > > Another option would be to return NULL if it's > > > > used from krealloc with a pointer into rodata > > [] > > > > diff --git a/mm/slab_common.c b/mm/slab_common.c > > [] > > > > @@ -1683,6 +1683,9 @@ static __always_inline void *__do_krealloc(const void *p, size_t new_size, > > > > * @new_size: how many bytes of memory are required. > > > > * @flags: the type of memory to allocate. > > > > * > > > > + * If the object pointed to is in rodata (likely from kstrdup_const) > > > > + * %NULL is returned. > > > > + * > > [] > > > Won't we have similar issues if somebody would do a kfree() instead of a > > > kfree_const()? So I think the original patch makes sense. > > > > Which is why I also suggested making kfree work for > > more types of memory freeing earlier this month. > > > > https://lore.kernel.org/lkml/573b3fbd5927c643920e1364230c296b23e7584d.camel@perches.com/ [] > what's the real benefit that is worth spending extra runtime cycles? I very much doubt there is an actual instance where the runtime cycles matter. Where could there be a fast-path instance of free? ANd kvfree consolidation and coding simplicity make it somewhat useful.