linux-kernel - Re: [PATCH] kdump/kexec: calculate note size at compile time

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Message-ID: <20070329034839.GA5973@verge.net.au>
Date:	Thu, 29 Mar 2007 12:48:40 +0900
From:	Simon Horman <horms@...ge.net.au>
To:	Vivek Goyal <vgoyal@...ibm.com>
Cc:	fastboot@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] kdump/kexec: calculate note size at compile time

On Thu, Mar 29, 2007 at 09:14:21AM +0530, Vivek Goyal wrote:
> On Thu, Mar 29, 2007 at 12:30:59PM +0900, Simon Horman wrote:
> > Hi,
> > 
> > this is a(nother) minor update to this patch. 
> > Explanation below.
> > 
> > -- 
> > Horms
> >   H: http://www.vergenet.net/~horms/
> >   W: http://www.valinux.co.jp/en/
> > 
> > [PATCH] kdump/kexec: calculate note size at compile time
> > 
> > Currently the size of the per-cpu region reserved to save crash
> > notes is set by the per-architecture value MAX_NOTE_BYTES. Which
> > in turn is currently set to 1024 on all supported architectures.
> > 
> > While testing ia64 I recently discovered that this value is
> > in fact too small. The particular setup I was using actually
> > needs 1172 bytes. This lead to very tedious failure mode
> > where the tail of one elf note would overwrite the head of
> > another if they ended up being alocated sequentially by kmalloc,
> > which was often the case.
> > 
> > It seems to me that a far better approach is to caclculate the size
> > that the area needs to be. This patch does just that.
> > 
> > If a simpler stop-gap patch for ia64 to be squeezed into 2.6.21(.X)
> > is needed then this should be as easy as making MAX_NOTE_BYTES
> > larger in arch/asm-ia64/kexec.h. Perhaps 2048 would be a good choice.
> > However, I think that the approach in this patch is a much more robust
> > idea.
> > 
> > Update I:
> > 
> >   Changed KEXEC_NOTE_HEAD_BYTES to KEXEC_NOTE_DESC_BYTES in line
> >   with the name of the relevant field in struct elf_note
> > 
> > Update II:
> > 
> >   * Use KEXEC_NOTE_NAME instead of "CORE" in kernel/kexec.c and
> >     arch/ia64/kernel/crash.c just to be extra sure that the data
> >     used to calculate the size, and the data stuffed into the reserved
> >     area is the same.
> > 
> >     Incidently, the ia64 code really ought to use the generic code.
> >     I am working on a patch for this. But it is not urgent.
> > 
> 
> Looks good. Another patch to make ia64 also use generic kexec code
> for note generation would be nice.

Thanks, I will make it so :-)

-- 
Horms
  H: http://www.vergenet.net/~horms/
  W: http://www.valinux.co.jp/en/

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