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 CD608C7EE23 for ; Wed, 31 May 2023 00:18:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233797AbjEaASx (ORCPT ); Tue, 30 May 2023 20:18:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45538 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231348AbjEaASl (ORCPT ); Tue, 30 May 2023 20:18:41 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 556E2F3 for ; Tue, 30 May 2023 17:18:00 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685492279; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=baSFBqUUVIrLoDCDA2ucQJhIAa+yyQWxP1bD9ZLCVTk=; b=W1YqhH2OeA3C5Wws5uw8Asb0FfAV0MW+Ak5nOk/RzszWRT0Q0nVFnnCw2p9dduCUcOAKqV lQmfl+ZedAdpDLo0FTkMSyoMkMMmCF9JrByVgQ2uvSUBrZGHMlJJU1zOQ5MosuunZvERIp 2sCJIeeEEN4IAILWKHRaTalrErmoVy0= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-516-NsKU-DCeN1KOYrl-AbZAIQ-1; Tue, 30 May 2023 20:17:56 -0400 X-MC-Unique: NsKU-DCeN1KOYrl-AbZAIQ-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id ECA7C1C05B04; Wed, 31 May 2023 00:17:55 +0000 (UTC) Received: from localhost (ovpn-12-54.pek2.redhat.com [10.72.12.54]) by smtp.corp.redhat.com (Postfix) with ESMTPS id EE9D3492B0A; Wed, 31 May 2023 00:17:54 +0000 (UTC) Date: Wed, 31 May 2023 08:17:51 +0800 From: Baoquan He To: Zhen Lei Cc: Eric Biederman , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, Michael Holzheu , Andrew Morton Subject: Re: [PATCH 2/6] kexec: delete a useless check in crash_shrink_memory() Message-ID: References: <20230527123439.772-1-thunder.leizhen@huawei.com> <20230527123439.772-3-thunder.leizhen@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230527123439.772-3-thunder.leizhen@huawei.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? > > 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 >