linux-kernel - Re: [PATCH] hv: use correct order when freeing monitor

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Date:	Wed, 28 May 2014 09:20:21 +0800
From:	Amos Kong <akong@...hat.com>
To:	Radim Krčmář <rkrcmar@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jason Wang <jasowang@...hat.com>, stable@...r.kernel.org,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	devel@...uxdriverproject.org
Subject: Re: [PATCH] hv: use correct order when freeing monitor_pages

On Tue, May 27, 2014 at 07:16:20PM +0200, Radim Krčmář wrote:
> We try to free two pages when only one has been allocated.
> Cleanup path is unlikely, so I haven't found any trace that would fit,
> but I hope that free_pages_prepare() does catch it.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Radim Krčmář <rkrcmar@...hat.com>
> ---
>  Cc'd stable because the worst-case looks hard to debug.
>  Btw. the module can't get unloaded after we successfully connect?
> 
>  drivers/hv/connection.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index 7f10c15..e84f452 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -224,8 +224,8 @@ cleanup:
>  		vmbus_connection.int_page = NULL;
>  	}
>  
> -	free_pages((unsigned long)vmbus_connection.monitor_pages[0], 1);
> -	free_pages((unsigned long)vmbus_connection.monitor_pages[1], 1);
> +	free_pages((unsigned long)vmbus_connection.monitor_pages[0], 0);
> +	free_pages((unsigned long)vmbus_connection.monitor_pages[1], 0);


Allocate order is 0. (2^0 = 1 page)

  vmbus_connection.monitor_pages[0] = (void *)__get_free_pages((GFP_KERNEL|__GFP_ZERO), 0);
  vmbus_connection.monitor_pages[1] = (void *)__get_free_pages((GFP_KERNEL|__GFP_ZERO), 0);

Looks good.

Reviewed-by: Amos Kong <akong@...hat.com>

>  	vmbus_connection.monitor_pages[0] = NULL;
>  	vmbus_connection.monitor_pages[1] = NULL;
>  
> -- 
> 1.9.3
> 
> --
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-- 
			Amos.
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