linux-kernel - Re: [PATCH] x86, vm86: fix preemption bug for int3 breakpoint handlers.

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Message-ID: <alpine.LFD.2.00.0905251225190.3582@localhost.localdomain>
Date:	Mon, 25 May 2009 12:33:20 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Bart Oldeman <bartoldeman@...rs.sourceforge.net>
cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, stable@...nel.org
Subject: Re: [PATCH] x86, vm86: fix preemption bug for int3 breakpoint
 handlers.

Bart,

On Sun, 24 May 2009, Bart Oldeman wrote:
> diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c
> index b8035a0..17c7734 100644
> --- a/arch/x86/kernel/vm86_32.c
> +++ b/arch/x86/kernel/vm86_32.c
> @@ -551,8 +551,12 @@ cannot_handle:
>  int handle_vm86_trap(struct kernel_vm86_regs *regs, long error_code, int
> trapno)
>  {
>  	if (VMPI.is_vm86pus) {
> -		if ((trapno == 3) || (trapno == 1))
> +		if ((trapno == 3) || (trapno == 1)) {
> +			/* re-enable preemption: return_to_32bit()
> +			   jumps straight to entry_32.S */
> +			dec_preempt_count();

  This will break other callers of handle_vm86_trap().

Thanks,

	tglx

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