Subject: Re: PFs on pages pinned with get_user_pages()
From: Peter Zijlstra <peterz@infradead.org>
To: Frank Mehnert <Frank.Mehnert@Sun.COM>
Cc: linux-kernel@vger.kernel.org
In-Reply-To: <200901291502.48312.frank.mehnert@sun.com>
References: <200901290905.10966.frank.mehnert@sun.com>
	 <200901291408.02454.frank.mehnert@sun.com>
	 <1233236630.4495.80.camel@laptop>
	 <200901291502.48312.frank.mehnert@sun.com>
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Date: Thu, 29 Jan 2009 15:20:54 +0100
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On Thu, 2009-01-29 at 15:02 +0100, Frank Mehnert wrote:

> I'm one of the VirtualBox developers. We are trying to fix the annoying
> kerneloops warning 'BUG: sleeping function called from invalid context'
> reported by the Fedora folks. This warning occurs when do_swap_page()
> calls lock_page() and in_atomic() returns true.
> 
> This warning appears when we touch into memory which is pinned with
> get_user_pages(). In VT-x/AMD-V mode we are executing some code in the
> context of the Linux kernel. To prevent scheduling of the current CPU
> core we disable the interripts. preempt_disable() would be probably the
> better choice but this would oops as well if CONFIG_PREEMPT is enabled.

but to get there, you'd have to have called handle_mm_fault() which
requires the mmap_sem, which should also give that might_sleep()
warning.

That aside, is there any reason you have to avoid scheduling? Otherwise
I would just allow so and be done with it.

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