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 EAEB5C74A5B for ; Fri, 17 Mar 2023 09:07:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230406AbjCQJHF (ORCPT ); Fri, 17 Mar 2023 05:07:05 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50522 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230490AbjCQJGg (ORCPT ); Fri, 17 Mar 2023 05:06:36 -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 D89CF10EA8A for ; Fri, 17 Mar 2023 02:04:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1679043854; 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=OQdgWFc6bLqbUjsOerHrtF2OlkuzdzQLwLSMHD36fpI=; b=hgumKmmXDD4JxkvyJYvd7CUaNpHamx4HiswLbuib7nkKROATLOZOnaHNQMonlKEstmw39T fy9mnf0zDGBl5FGUloAX7ONNYkXa+Hp2R0xWwEK7QnfZ8Oe8IZc1eJqdKY90KmlvhVhcFe azGXZXQT67FdvOL9C+qJOq+D5K7vTZY= 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-488-bnocHIOQPXazumCh-Gg7zw-1; Fri, 17 Mar 2023 05:04:10 -0400 X-MC-Unique: bnocHIOQPXazumCh-Gg7zw-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 6B4C31C087A7; Fri, 17 Mar 2023 09:04:07 +0000 (UTC) Received: from localhost (ovpn-12-67.pek2.redhat.com [10.72.12.67]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 317A540C6E67; Fri, 17 Mar 2023 09:04:06 +0000 (UTC) Date: Fri, 17 Mar 2023 17:04:01 +0800 From: Baoquan He To: Eric DeVolder Cc: linux-kernel@vger.kernel.org, x86@kernel.org, kexec@lists.infradead.org, ebiederm@xmission.com, dyoung@redhat.com, vgoyal@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com, robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com, sourabhjain@linux.ibm.com, konrad.wilk@oracle.com, boris.ostrovsky@oracle.com Subject: Re: [PATCH v19 2/7] crash: add generic infrastructure for crash hotplug support Message-ID: References: <20230306162228.8277-1-eric.devolder@oracle.com> <20230306162228.8277-3-eric.devolder@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 03/16/23 at 09:44am, Eric DeVolder wrote: > > > On 3/16/23 05:11, Baoquan He wrote: > > On 03/06/23 at 11:22am, Eric DeVolder wrote: > > ...... > > > +static void crash_handle_hotplug_event(unsigned int hp_action, unsigned int cpu) > > > +{ > > > + /* Obtain lock while changing crash information */ > > > + if (kexec_trylock()) { > > > + > > > + /* Check kdump is loaded */ > > > + if (kexec_crash_image) { > > > + struct kimage *image = kexec_crash_image; > > > + > > > + if (hp_action == KEXEC_CRASH_HP_ADD_CPU || > > > + hp_action == KEXEC_CRASH_HP_REMOVE_CPU) > > > + pr_debug("hp_action %u, cpu %u\n", hp_action, cpu); > > > + else > > > + pr_debug("hp_action %u\n", hp_action); > > > + > > > + /* > > > + * When the struct kimage is allocated, the elfcorehdr_index > > > + * is set to -1. Find the segment containing the elfcorehdr, > > > + * if not already found. This works for both the kexec_load > > > + * and kexec_file_load paths. > > > + */ > > > + if (image->elfcorehdr_index < 0) { > > > + unsigned long mem; > > > + unsigned char *ptr; > > > + unsigned int n; > > > + > > > + for (n = 0; n < image->nr_segments; n++) { > > > + mem = image->segment[n].mem; > > > + ptr = kmap_local_page(pfn_to_page(mem >> PAGE_SHIFT)); > > > + if (ptr) { > > > + /* The segment containing elfcorehdr */ > > > + if (memcmp(ptr, ELFMAG, SELFMAG) == 0) { > > > + image->elfcorehdr_index = (int)n; > > > + } > > > + kunmap_local(ptr); > > > + } > > > + } > > > + } > > > + > > > + if (image->elfcorehdr_index < 0) { > > > + pr_err("unable to locate elfcorehdr segment"); > > > + goto out; > > > + } > > > + > > > + /* Needed in order for the segments to be updated */ > > > + arch_kexec_unprotect_crashkres(); > > > + > > > + /* Differentiate between normal load and hotplug update */ > > > + image->hp_action = hp_action; > > > + > > > + /* Now invoke arch-specific update handler */ > > > + arch_crash_handle_hotplug_event(image); > > > + > > > + /* No longer handling a hotplug event */ > > > + image->hp_action = KEXEC_CRASH_HP_NONE; > > > + image->elfcorehdr_updated = true; > > > > It's good to initialize the image->hp_action here, however where do > > you check it? Do you plan to add some check somewhere? > > Hi Baoquan, > The hp_action member is initialized to 0 in do_image_alloc_init(). I've > mapped KEXEC_CRASH_HP_NONE onto 0 on purpose. > > But the use of image->hp_action = KEXEC_CRASH_HP_NONE is to actually > delineate that a hotplug event handling has completed. You can see > imae->hp_action set to hp_action to capture what the triggering event > was, as passed into this function. > > I will go ahead and set image->hp_action = KEXEC_CRASH_HP_NONE; explicitly > in do_kimage_alloc_init(), as that is done for the other crash hotplug members. Yeah, setting image->hp_action = KEXEC_CRASH_HP_NONE in do_kimage_alloc_init() will make code clearer. While I am wondering if we don't initialie image->hp_action to KEXEC_CRASH_HP_NONE, and don't set image->hp_action to KEXEC_CRASH_HP_NONE to actually delineate that a hotplug event handling has completed, what will happen? I mean you set image->hp_action to KEXEC_CRASH_HP_NONE explicitly, where do you check if it should not be KEXEC_CRASH_HP_NONE? In crash_handle_hotplug_event(), we took __kexec_lock and assign the passed hp_action anyway.