linux-kernel - Re: [PATCH] dvb: siano: free spinlock before schedule()

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Date:	Wed, 28 Jul 2010 00:24:39 +0200
From:	Jiri Slaby <jirislaby@...il.com>
To:	Kulikov Vasiliy <segooon@...il.com>
CC:	kernel-janitors@...r.kernel.org,
	Mauro Carvalho Chehab <mchehab@...radead.org>,
	Douglas Schilling Landgraf <dougsland@...hat.com>,
	Jiri Kosina <jkosina@...e.cz>,
	Roel Kluin <roel.kluin@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
	Richard Zidlicky <rz@...ux-m68k.org>
Subject: Re: [PATCH] dvb: siano: free spinlock before schedule()

On 07/27/2010 08:42 PM, Kulikov Vasiliy wrote:
> Calling schedule() holding spinlock with disables irqs is improper. As
> spinlock protects list coredev->buffers, it can be unlocked untill wakeup.
> This bug was introduced in a9349315f65cd6a16e8fab1f6cf0fd40f379c4db.
> 
> Signed-off-by: Kulikov Vasiliy <segooon@...il.com>
> ---
>  drivers/media/dvb/siano/smscoreapi.c |    6 ++++--
>  1 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/media/dvb/siano/smscoreapi.c b/drivers/media/dvb/siano/smscoreapi.c
> index 7f2c94a..d93468c 100644
> --- a/drivers/media/dvb/siano/smscoreapi.c
> +++ b/drivers/media/dvb/siano/smscoreapi.c
> @@ -1113,9 +1113,11 @@ struct smscore_buffer_t *smscore_getbuffer(struct smscore_device_t *coredev)
>  	 */
>  
>  	prepare_to_wait(&coredev->buffer_mng_waitq, &wait, TASK_INTERRUPTIBLE);
> -
> -	if (list_empty(&coredev->buffers))
> +	if (list_empty(&coredev->buffers)) {
> +		spin_unlock_irqrestore(&coredev->bufferslock, flags);
>  		schedule();
> +		spin_lock_irqsave(&coredev->bufferslock, flags);
> +	}
>  
>  	finish_wait(&coredev->buffer_mng_waitq, &wait);

There is a better fix (which fixes the potential NULL dereference):
http://lkml.org/lkml/2010/6/7/175

Richard, could you address the comments there and resend?

regards,
-- 
js
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