Re: [PATCH] pcmcia/pccard deadlock fix

["Markus Rechberger" <markus.rechberger@amd.com>]

Andrew Morton wrote:
> > 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@amd.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@amd.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?
>   
The userspace application should return the appropriate error then. It 
can really happen any time when someone tries to eject the pcmcia device 
(any time as within 1 minute - never in a normal scenario)

> 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?
>
>   
There's a description about it in following Email:
http://lkml.org/lkml/2007/2/19/58

Markus


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