Re: [PATCH 1/5] Use mutex instead of semaphore in the Host APdriver

[Satyam Sharma]

On Mon, 30 Jul 2007, Michael Buesch wrote:

> On Sunday 29 July 2007 23:34, Matthias Kaehlcke wrote:
> > The Host AP driver uses a semaphore as mutex. Use the mutex API
> > instead of the (binary) semaphore.
> > 
> > Signed-off-by: Matthias Kaehlcke <matthias.kaehlcke@xxxxxxxxx>

[ Something seems to have gone wrong with your diff / patch / script.
  There was no diff header here, which should have been. ]

> > -	res = down_interruptible(&local->rid_bap_sem);
> > +	res = mutex_lock_interruptible(&local->rid_bap_mtx);
> >  	if (res)
> >  		return res;
> >  
> > @@ -902,7 +902,7 @@ static int hfa384x_set_rid(struct net_device *dev, u16 rid, void *buf, int len)
> >  	/* RID len in words and +1 for rec.rid */
> >  	rec.len = cpu_to_le16(len / 2 + len % 2 + 1);
> >  
> > -	res = down_interruptible(&local->rid_bap_sem);
> > +	res = mutex_lock_interruptible(&local->rid_bap_mtx);
> >  	if (res)
> >  		return res;
> >  
> 
> Is res returned to userspace? If yes, that's not right.

Yup, that's not right.

> On a interrupted mutex allocation you should return
> -ERESTARTSYS to userspace.

Nope, userspace must not see ERESTARTSYS (I /think/ this is the third
time I'm participating in this exact same discussion :-)

If the return would be caught by a previous in-kernel caller in the
call chain, ERESTARTSYS is okay and it could try to restart the
operation. However, if the return goes unfiltered directly to
userspace, EINTR is the correct choice.


Satyam
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