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 36A43C7EE2C for ; Wed, 31 May 2023 02:19:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234011AbjEaCT6 (ORCPT ); Tue, 30 May 2023 22:19:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54580 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234009AbjEaCT4 (ORCPT ); Tue, 30 May 2023 22:19:56 -0400 Received: from szxga02-in.huawei.com (szxga02-in.huawei.com [45.249.212.188]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B071C113 for ; Tue, 30 May 2023 19:19:54 -0700 (PDT) Received: from dggpemm500006.china.huawei.com (unknown [172.30.72.53]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4QWCdV68m0zTkwp; Wed, 31 May 2023 10:19:42 +0800 (CST) Received: from [10.174.178.55] (10.174.178.55) by dggpemm500006.china.huawei.com (7.185.36.236) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.23; Wed, 31 May 2023 10:19:52 +0800 Subject: Re: [PATCH 2/6] kexec: delete a useless check in crash_shrink_memory() To: Baoquan He CC: Eric Biederman , , , Michael Holzheu , Andrew Morton References: <20230527123439.772-1-thunder.leizhen@huawei.com> <20230527123439.772-3-thunder.leizhen@huawei.com> From: "Leizhen (ThunderTown)" Message-ID: <5beb1883-5391-1b75-d8cd-2152478b9e72@huawei.com> Date: Wed, 31 May 2023 10:19:51 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.178.55] X-ClientProxiedBy: dggems705-chm.china.huawei.com (10.3.19.182) To dggpemm500006.china.huawei.com (7.185.36.236) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/5/31 8:17, Baoquan He wrote: > On 05/27/23 at 08:34pm, Zhen Lei wrote: >> The check '(crashk_res.parent != NULL)' is added by >> commit e05bd3367bd3 ("kexec: fix Oops in crash_shrink_memory()"), but it's >> stale now. Because if 'crashk_res' is not reserved, it will be zero in >> size and will be intercepted by the above 'if (new_size >= old_size)'. >> >> Ago: >> if (new_size >= end - start + 1) >> >> Now: >> old_size = (end == 0) ? 0 : end - start + 1; >> if (new_size >= old_size) > > Hmm, I would strongly suggest we keep that check. Even though the > current code like above can do the acutal checking, but its actual usage > is not obvious for checking of crashk_res existence. In the future, > someone may change above calculation and don't notice the hidden > functionality at all behind the calculation. The cost of the check is > almost zero, right? The cost of the check is negligible. The only downside is that it's hard to understand why it's added, and I only found out why by looking at the history log. In my opinion, the above 'Now:' is the right fix. > >> >> Signed-off-by: Zhen Lei >> --- >> kernel/kexec_core.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c >> index 22acee18195a591..d1ab139dd49035e 100644 >> --- a/kernel/kexec_core.c >> +++ b/kernel/kexec_core.c >> @@ -1137,7 +1137,7 @@ int crash_shrink_memory(unsigned long new_size) >> end = start + new_size; >> crash_free_reserved_phys_range(end, crashk_res.end); >> >> - if ((start == end) && (crashk_res.parent != NULL)) >> + if (start == end) >> release_resource(&crashk_res); >> >> ram_res->start = end; >> -- >> 2.25.1 >> > > . > -- Regards, Zhen Lei