linux-kernel - Re: [Bugme-new] [Bug 13850] New: reading /proc/kcore causes oops

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Date:	Wed, 29 Jul 2009 12:32:09 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Mike Smith <scgtrp@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	bugzilla-daemon@...zilla.kernel.org,
	bugme-daemon@...zilla.kernel.org,
	Amerigo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [Bugme-new] [Bug 13850] New: reading /proc/kcore causes oops

On Tue, 28 Jul 2009 22:46:56 -0400
Mike Smith <scgtrp@...il.com> wrote:

> > What's layout of memory does your server have ?
> The log I gave was from my desktop, so I'll assume you wanted that
> instead of the server:
> [mike: mike in ~]$ grep "System RAM" /proc/iomem
> 00010000-0009efff : System RAM
> 00100000-1dedffff : System RAM
> 
>From this, your kernel's valid direct-map address range will be

c0010000-c009efff
c0100000-ddedffff

And, 
==
unable to handle kernel paging request at e07cf000
==
e07cf000 doesn't exist in direct map. It seems this is vmalloc() area.

At looking into mm/vmalloc.c, this area is unmapped under
- purge_lock
But proc/kcore just access this just under vmlist_lock.

No guards at all. This is _a_ problem. But it seems race is not
reproducable easily. I'll think more but is it guaranteed whether
vmalloc area(struct vm_struct) linked to vmlist has always valid pages ?
Considering get_vm_area(), it's not true I think.

I wonder fs/proc/kcore.c's vmalloc area access needs some fix. let me try.

Thanks,
-Kame





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