linux-kernel - Re: [PATCH] MTRR: Fix race causing set

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Date:	Mon, 25 Jun 2007 18:05:17 -0400
From:	Chuck Ebbert <cebbert@...hat.com>
To:	Loic Prylli <loic@...i.com>
CC:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...e.de>
Subject: Re: [PATCH] MTRR: Fix race causing set_mtrr to go into infinite loop

On 06/25/2007 05:38 PM, Loic Prylli wrote:

[cc: Andi]

> Processors synchronization in set_mtrr requires the .gate field
> to be set after .count field is properly initialized. Without an explicit
> barrier, the compiler was reordering those memory stores. That was sometimes
> causing a processor (in ipi_handler) to see the .gate change and
> decrement .count before the latter is set by set_mtrr() (which
> then hangs in a infinite loop with irqs disabled).
> 
> Signed-off-by: Loic Prylli <loic@...i.com>
> ---
>  arch/i386/kernel/cpu/mtrr/main.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/i386/kernel/cpu/mtrr/main.c b/arch/i386/kernel/cpu/mtrr/main.c
> index 55b0051..75dc6d5 100644
> --- a/arch/i386/kernel/cpu/mtrr/main.c
> +++ b/arch/i386/kernel/cpu/mtrr/main.c
> @@ -229,6 +229,8 @@ static void set_mtrr(unsigned int reg, unsigned long base,
>  	data.smp_size = size;
>  	data.smp_type = type;
>  	atomic_set(&data.count, num_booting_cpus() - 1);
> +	/* make sure data.count is visible before unleashing other CPUs */
> +	smp_wmb();
>  	atomic_set(&data.gate,0);
>  
>  	/*  Start the ball rolling on other CPUs  */
> @@ -242,6 +244,7 @@ static void set_mtrr(unsigned int reg, unsigned long base,
>  
>  	/* ok, reset count and toggle gate */
>  	atomic_set(&data.count, num_booting_cpus() - 1);
> +	smp_wmb();
>  	atomic_set(&data.gate,1);
>  
>  	/* do our MTRR business */
> @@ -260,6 +263,7 @@ static void set_mtrr(unsigned int reg, unsigned long base,
>  		cpu_relax();
>  
>  	atomic_set(&data.count, num_booting_cpus() - 1);
> +	smp_wmb();
>  	atomic_set(&data.gate,0);
>  
>  	/*
-
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