Re: [PATCH] NFC: Driver for Inside Secure MicroRead NFC chip

[Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>]

On Friday 18 March 2011, Mark Brown wrote:
> On Fri, Mar 18, 2011 at 01:19:53PM +0100, Arnd Bergmann wrote:
> > On Friday 18 March 2011, Waldemar Rymarkiewicz wrote:
> 
> > > +
> > > +   mutex_lock(&info->rx_mutex);
> > > +   info->irq_state = 1;
> > > +   mutex_unlock(&info->rx_mutex);
> > > +
> > > +   wake_up_interruptible(&info->rx_waitq);
> > > +
> > > +   return IRQ_HANDLED;
> > > +}
> 
> > You cannot take a mutex from interrupt context, that may
> > cause deadlocks.
> 
> This is a threaded IRQ handler so mutexes are fine.

Ah, right. I've never seen one of these used in the field,
so I didn't think of this.

Looking at the mutexes though: The read function does
not hold the rx_mutex when reading the irq_state
variable, so that is potentially racy.

The read function seems to have another problem regarding
the user space buffer: it bails out if the provided buffer
is larger than the available data, which is pointless,
but it does not check if the user buffer is too short.

	Arnd