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Date: Thu, 08 Mar 2001 21:12:52 +0100
From: Manfred Spraul <manfred@colorfullife.com>
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To: Rik van Riel <riel@conectiva.com.br>
CC: linux-kernel@vger.kernel.org
Subject: Re: BUG? race between kswapd and ptrace (access_process_vm )
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Rik van Riel wrote:
> 
> On Wed, 7 Mar 2001, Manfred Spraul wrote:
> 
> > Is kswapd now running without lock_kernel()?
> 
> Indeed ...
> 
> > Then there is a race between swapout and ptrace:
> > access_process_vm() accesses the page table entries, only protected with
> > the mmap_sem semaphore and lock_kernel().
> >
> > Isn't
> >
> >     spin_lock(&mm->page_table_lock);
> >
> > missing in access_one_page() [in linux/kernel/ptrace.c]?
> 
> You're probably right here ...
>

Fixing the bug is more difficult than I thought:

Initially I assumed it would be a two-liner (lock, unlock) but kmap()
can sleep.

Can I reuse a kmap_atomic() type or should I add a new type?

I could add local_irq_save() and (ab)use KMAP_BOUNCE_READ, but I'm not
sure if that's the Right Thing(tm)

--
	Manfred