Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932570Ab2CACun (ORCPT ); Wed, 29 Feb 2012 21:50:43 -0500 Received: from kirsty.vergenet.net ([202.4.237.240]:50373 "EHLO kirsty.vergenet.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932216Ab2CACum (ORCPT ); Wed, 29 Feb 2012 21:50:42 -0500 Date: Thu, 1 Mar 2012 11:50:39 +0900 From: Simon Horman To: HATAYAMA Daisuke Cc: surovegin@google.com, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, vgoyal@redhat.com, ebiederm@xmission.com Subject: Re: [PATCH] kdump: force page alignment for per-CPU crash notes. Message-ID: <20120301025038.GD10053@verge.net.au> References: <20120301013200.GF16483@verge.net.au> <20120301.105126.193682835.d.hatayama@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120301.105126.193682835.d.hatayama@jp.fujitsu.com> Organisation: Horms Solutions Ltd. User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2881 Lines: 71 On Thu, Mar 01, 2012 at 10:51:26AM +0900, HATAYAMA Daisuke wrote: > From: Eugene Surovegin > Subject: Re: [PATCH] kdump: force page alignment for per-CPU crash notes. > Date: Wed, 29 Feb 2012 17:39:55 -0800 > > > On Wed, Feb 29, 2012 at 5:32 PM, Simon Horman wrote: > >> On Wed, Feb 29, 2012 at 05:23:10PM -0800, Eugene Surovegin wrote: > >>> On Wed, Feb 29, 2012 at 5:18 PM, Simon Horman wrote: > >>> > >>> > On Wed, Feb 29, 2012 at 09:21:23AM -0800, Eugene Surovegin wrote: > >>> > > Per-CPU allocations are not guaranteed to be physically contiguous. > >>> > > However, kdump kernel and user-space code assumes that per-CPU > >>> > > memory, used for saving CPU registers on crash, is. > >>> > > This can cause corrupted /proc/vmcore in some cases - the main > >>> > > symptom being huge ELF note section. > >>> > > > >>> > > Force page alignment for note_buf_t to ensure that this assumption holds. > >>> > > >>> > Ouch. I'm surprised there is an allocation on crash, perhaps > >>> > it could at least be done earlier? And am I right in thinking > >>> > that this change increases the likely hood that the allocation > >>> > could fail? > >>> > > >>> > >>> I'm not following. This allocation is done on start-up, not on crash. > >>> If you cannot allocate this much memory on system boot, I'm not sure what > >>> else you can do on this system.... > >> > >> Sorry, my eyes deceived me. You are correct and I agree. > >> > >> Is it the case that note_buf_t is never larger than PAGE_SIZE? > >> If so I your patch looks good to me. > > > > Currently, maximum note size is hardcoded in kexec-tools to 1024 > > (MAX_NOTE_BYTES). > > Usually it's way less. IIRC on x86_64 it's 336 bytes. I presume that MAX_NOTE_BYTES was chosen to be large to minimise the chance that it would ever need to be changed. > This is elf_prstatus and I guess it's mostly equal to registers. > > crash> p sizeof(struct elf_prstatus) > $3 = 336 > crash> ptype struct elf_prstatus > type = struct elf_prstatus { > struct elf_siginfo pr_info; > short int pr_cursig; > long unsigned int pr_sigpend; > long unsigned int pr_sighold; > pid_t pr_pid; > pid_t pr_ppid; > pid_t pr_pgrp; > pid_t pr_sid; > struct timeval pr_utime; > struct timeval pr_stime; > struct timeval pr_cutime; > struct timeval pr_cstime; > elf_gregset_t pr_reg; <-- this > int pr_fpvalid; > } > > What kinds of architecture does have so many registers? It's just my > interest. Or possibly other kinds of notes is written here? The winner seems to be ia64 with 128. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/