Date: Thu, 29 Jan 2009 15:59:21 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Frank Mehnert <Frank.Mehnert@Sun.COM>, linux-kernel@vger.kernel.org,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Nick Piggin <npiggin@suse.de>
Subject: Re: [PATCH] x86: add might_sleep() to do_page_fault()
Message-ID: <20090129145921.GC6512@elte.hu>
References: <200901290905.10966.frank.mehnert@sun.com> <200901291502.48312.frank.mehnert@sun.com> <1233238854.4495.93.camel@laptop> <200901291541.32618.frank.mehnert@sun.com> <1233241003.4495.97.camel@laptop>
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* Peter Zijlstra <peterz@infradead.org> wrote:

> VirtualBox calls do_page_fault() from an atomic context but runs into a
> might_sleep() way pas this point, cure that.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
>  arch/x86/mm/fault.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 67e4df5..bb7f946 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -908,6 +908,11 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code)
>  		}
>  		down_read(&mm->mmap_sem);
>  	}
> +	/*
> +	 * The above down_read_trylock() might have succeeded in which case
> +	 * we'll have missed the might_sleep() from down_read().
> +	 */
> +	might_sleep();

should go into the 'else' branch i guess? In the down_read() case we 
already had the check.

	Ingo
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