linux-kernel - Re: PFs on pages pinned with get_user

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Message-Id: <1233238854.4495.93.camel@laptop>
Date:	Thu, 29 Jan 2009 15:20:54 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Frank Mehnert <Frank.Mehnert@....COM>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: PFs on pages pinned with get_user_pages()

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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