From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759481AbYG2PQB (ORCPT ); Tue, 29 Jul 2008 11:16:01 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756757AbYG2PPm (ORCPT ); Tue, 29 Jul 2008 11:15:42 -0400 Received: from mx1.redhat.com ([66.187.233.31]:35024 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754102AbYG2PPk (ORCPT ); Tue, 29 Jul 2008 11:15:40 -0400 Date: Tue, 29 Jul 2008 11:15:33 -0400 From: Vivek Goyal To: Simon Horman Cc: kexec@lists.infradead.org, linux-ia64@vger.kernel.org, linux kernel mailing list Subject: Re: [patch 2/3] kdump: add is_vmcore_usable() and vmcore_unusable() Message-ID: <20080729151533.GP25975@redhat.com> References: <20080729081235.293361145@vergenet.net> <20080729081629.522008269@vergenet.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080729081629.522008269@vergenet.net> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 29, 2008 at 06:12:37PM +1000, Simon Horman wrote: > The usage of elfcorehdr_addr has changed recently > such that being set to ELFCORE_ADDR_MAX is used by > is_kdump_kernel() to indicate if the code is executing > in a kernel executed as a crash kernel. > > However, arch/ia64/kernel/setup.c:reserve_elfcorehdr will > rest elfcorehdr_addr to ELFCORE_ADDR_MAX on error, > which means any subsequent calls to is_kdump_kernel() > will return 0, even though they should return 1. > > Ok, at this point in time there are no subsequent calls, > but I think its fair to say that there is ample scope for error > or at the very least confusion. > > This patch add an extra state, ELFCORE_ADDR_ERR, which > indicates that elfcorehdr_addr was passed on the command line, > and thus execution is taking place in a crashdump kernel, > but vmcore can't be used for some reason. This is tested > for using is_vmcore_usable() and set using vmcore_unusable(). > A subsequent patch makes use of this new code. > > To summarise, the states that elfcorehdr_addr can now be in are as follows: > > ELFCORE_ADDR_MAX: not a crashdump kernel > ELFCORE_ADDR_ERR: crashdump kernel but vmcore is unusable > any other value: crash dump kernel and vmcore is usable > > Signed-off-by: Simon Horman > > > Index: linux-2.6/include/linux/crash_dump.h > =================================================================== > --- linux-2.6.orig/include/linux/crash_dump.h 2008-07-29 17:27:43.000000000 +1000 > +++ linux-2.6/include/linux/crash_dump.h 2008-07-29 17:53:13.000000000 +1000 > @@ -8,6 +8,7 @@ > #include > > #define ELFCORE_ADDR_MAX (-1ULL) > +#define ELFCORE_ADDR_ERR (-2ULL) > > #ifdef CONFIG_PROC_VMCORE > extern unsigned long long elfcorehdr_addr; > @@ -36,5 +37,30 @@ static inline int is_kdump_kernel(void) > static inline int is_kdump_kernel(void) { return 0; } > #endif /* CONFIG_CRASH_DUMP */ > > +#ifdef CONFIG_PROC_VMCORE > +/* is_vmcore_usable() checks if the kernel is booting after a panic and > + * the vmcore region is usable. > + * > + * This makes use of the fact that due to alignment 1 is not > + * a valid pointer, much in the vain of IS_ERR(), except > + * dealing directly with an unsigned long long rather than a pointer. > + */ > + > +static inline int is_vmcore_usable(void) > +{ > + return is_kdump_kernel() && elfcorehdr_addr != ELFCORE_ADDR_ERR ? 1 : 0; > +} > + > +/* vmcore_unusable() marks the vmcore as unusable, without disturbing > + * the logic of is_kdump_kernel() > + */ > + > +static inline void vmcore_unusable(void) > +{ > + if (!is_kdump_kernel()) > + elfcorehdr_addr = ELFCORE_ADDR_ERR; > +} Hi Simon, Should above condition be "if(is_kdump_kernel())" instead of "if(!is_kdump_kernel())? I would think that you would like to mark a vmcore unusable only if, to begin with you were booting after a panic. If we being marking vmcore_unusable in case of normal kernel (!is_kdump_kernel()), then is_kdump_kernel() will start reporting normal kernel as kdump kernel? Thanks Vivek