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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B2AFCC77B7C for ; Wed, 31 May 2023 07:41:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=M8Z7fTHPcAzUue4hHgTCG/8u8kL3cqjwLQIJqey91p0=; b=OLfC3/+b6mm9i7 jmxViur+5Jy72k8rcXpQdfmkhGWYf0RMiSEnRCU/TQOXuTTnqyMxB/WAF9YmUNRnqwxQZrEAbBWpq 5ehIbSxqp8usOOHup1DkmIpUmUKluinC+fcMWp6mx/gE5llir36dbPDrbj6FZcaWeJn+t/aW3McBq 65HEQAaQOX2VJSV0Eknkldm/1v1lD2PBR94QrUVWxUSO61DuTzKuE10tk3DA6S1IsLElYBeYo3lna 8YIrcJUcNNsXLFG1sK8Exfgbzko0AJ7Fe4LfUgOzEAhVeVYaJojwWRnrES5rHGfv/s09o+Qgr/rOw ziOTI4puukD43tvYFS9A==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.96 #2 (Red Hat Linux)) id 1q4GSa-00GU4V-20; Wed, 31 May 2023 07:41:32 +0000 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by bombadil.infradead.org with esmtps (Exim 4.96 #2 (Red Hat Linux)) id 1q4GSY-00GU3U-1G for kexec@lists.infradead.org; Wed, 31 May 2023 07:41:31 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1685518889; 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=c/LgYdINnVSghmwNsV+kSfBQhPeozhgR1xVSC5icCD8=; b=iQun/tKlDAdKRrf20RQH/KsrpWbpIkA2AS8xuglaTm+dXHdNKi3q3QeQiSPARko0bD6gyV t2de6+rxNabGkE2yuO+Y17k4PlIBtgPEEjYetyq5LWiw0SyJU+B2trUE4mnBJ4MRzUeS9x xM9buD6xtc0rkxHxVbKgJ9xoVtPe3Ys= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-582-iC-EiwSvNPyI4SF233teJw-1; Wed, 31 May 2023 03:41:25 -0400 X-MC-Unique: iC-EiwSvNPyI4SF233teJw-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 5A5CF811E85; Wed, 31 May 2023 07:41:25 +0000 (UTC) Received: from localhost (ovpn-12-54.pek2.redhat.com [10.72.12.54]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6231F40C6EC4; Wed, 31 May 2023 07:41:22 +0000 (UTC) Date: Wed, 31 May 2023 15:41:20 +0800 From: Baoquan He To: "Leizhen (ThunderTown)" 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> <5beb1883-5391-1b75-d8cd-2152478b9e72@huawei.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <5beb1883-5391-1b75-d8cd-2152478b9e72@huawei.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230531_004130_524082_D57C681B X-CRM114-Status: GOOD ( 25.69 ) X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On 05/31/23 at 10:19am, Leizhen (ThunderTown) wrote: > > > 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. It checks if the resource exists before releasing, just a normal checking? > > > > >> > >> 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 > _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec