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Message-ID: <Pine.LNX.4.61.0707310557470.3926@mtfhpc.demon.co.uk>
Date: Tue, 31 Jul 2007 06:35:29 +0100 (BST)
From: Mark Fortescue <mark@...hpc.demon.co.uk>
To: David Miller <davem@...emloft.net>
cc: aaw@...gle.com, akpm@...ux-foundation.org,
linux-arch@...r.kernel.org, sparclinux@...r.kernel.org,
wli@...omorphy.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [SPARC32] NULL pointer derefference
Hi David,
>
> One possible issue is sequencing, perhaps the stack argument copy
> is occuring before the new context is setup properly on sun4c.
>
I think it is somthing related to this but too much has changed for me to
work out what is going on. At present, I don't have a good enough
understanding of the virtual memory system and how it interracts with the
sun4c mmu.
The original code did a job lot of pte stuf in install_arg_page. The new
code seems to replace this using get_user_pages but I have not worked out
how get_user_pages gets to the point at which it allocated pte's i.e.
maps the stack memory it is about to put the arguments into.
> Another issue might be the new flush_cache_page() call in this
> new code in fs/exec.c, there are now cases where flush_cache_page()
> will be called on kernel addresses, and sun4c's implementation might
> not like that at all.
I commented out the flush_cache_page callmade in the new code. This had no
effect on the problem. Other tests have shown it is breaking earlier than
this.
I am going to try to narrow down exactly where the pointer gets messed up
as this should help.
Regards
Mark Fortescue.
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