linux-kernel - Re: [PATCH] pcmcia/pccard deadlock fix

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Date:	Wed, 2 May 2007 14:20:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Markus Rechberger" <markus.rechberger@....com>
Cc:	linux-kernel@...r.kernel.org,
	Dominik Brodowski <linux@...inikbrodowski.net>
Subject: Re: [PATCH] pcmcia/pccard deadlock fix

> On Tue, 20 Feb 2007 16:08:11 +0100

20 Feb was a long time ago, sorry.  I was hoping to feed the pcmcia patches
through Dominik but I think he's busy with exams or such.  So I get to
pretend to be pcmcia maintainer.

"Markus Rechberger" <markus.rechberger@....com> wrote:

> following patch prevents a mutex/semaphore deadlock within the pcmcia
> framework when ejecting devices multiple times using pccardctl eject.
> 
> For some more details see:
> http://lkml.org/lkml/2007/2/19/58
> 
> Signed-off-by: Markus Rechberger <markus.rechberger@....com>
> 
> -- 
> Markus Rechberger
> Operating System Research Center
> AMD Saxony LLC & Co. KG
> 
> 
> 
> [pcmcia-pccard-deadlock-fix.diff  text/plain (757B)]
> index ac00424..c02bf0d 100644
> --- a/drivers/pcmcia/cs.c
> +++ b/drivers/pcmcia/cs.c
> @@ -856,7 +856,8 @@ int pcmcia_eject_card(struct pcmcia_socket *skt)
>      
>  	cs_dbg(skt, 1, "user eject request\n");
>  
> -	mutex_lock(&skt->skt_mutex);
> +	if (!mutex_trylock(&skt->skt_mutex)) 
> +		return -EAGAIN;
>  	do {
>  		if (!(skt->state & SOCKET_PRESENT)) {
>  			ret = -ENODEV;
> index 18e111e..b9d3440 100644
> --- a/drivers/pcmcia/ds.c
> +++ b/drivers/pcmcia/ds.c
> @@ -1100,7 +1100,9 @@ static ssize_t pcmcia_store_allow_func_id_match(struct device *dev,
>  	if (!count)
>  		return -EINVAL;
>  
> -	mutex_lock(&p_dev->socket->skt_mutex);
> +	if (!mutex_trylock(&p_dev->socket->skt_mutex)) 
> +		return -EAGAIN;
> +
>  	p_dev->allow_func_id_match = 1;
>  	mutex_unlock(&p_dev->socket->skt_mutex);
>  

This is a pretty sad-looking solution.  Does it not mean that sometimes
user-initiated actions will mysteriously fail?

Are you able to provide a more detailed description of why/how the deadlock
actually occurs so that perhaps a more robust fix can be implemented?

Thanks.
-
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