Re: [PATCH] use mutex instead of semaphore in RocketPort driver

[Robert Hancock <hancockr@shaw.ca>]

Matthias Kaehlcke wrote:
> El Tue, Apr 24, 2007 at 07:53:04PM +0200 Oliver Neukum ha dit:
>
> > Am Dienstag, 24. April 2007 19:49 schrieb Matthias Kaehlcke:
> > > @@ -1706,7 +1706,7 @@ static int rp_write(struct tty_struct *tty,
> > >         if (count <= 0 || rocket_paranoia_check(info, "rp_write"))
> > >                 return 0;
> > >  
> > > -       down_interruptible(&info->write_sem);
> > > +       mutex_lock_interruptible(&info->write_mtx);
> > This is a bug. It is also present in the current code, but nevertheless
> > it is a bug. If you use an interruptible lock, you must be ready to deal
> > with interrupts, which are ignored by this code.
>
> i fear i don't have the experience/knowledge to fix this bug, thanks
> for your remark. 
>
> i'm a bit confused now about the interruptible locks, i thought using
> them means that the process will be waked up when receiving a
> signal. what role are playing interrupts when using interruptible locks?

You are correct, interrupts aren't involved. However if the wait is 
interrupted by a signal, mutex_lock_interruptible will return a nonzero 
return code which needs to be checked for (and likely -ERESTARTSYS or 
-EINTR returned), otherwise the code will blindly continue as though it 
has locked the mutex even though it has not.

--
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@nospamshaw.ca
Home Page: http://www.roberthancock.com/

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