El Tue, May 22, 2007 at 09:59:01AM -0700 Arjan van de Ven ha dit:
> >
> > - down_interruptible(&info->write_sem);
> > + mutex_lock_interruptible(&info->write_mtx);
> >
> > #ifdef ROCKET_DEBUG_WRITE
> > printk(KERN_INFO "rp_write %d chars...", count);
> > @@ -1773,7 +1776,7 @@ end:
> > wake_up_interruptible(&tty->poll_wait);
> > #endif
> > }
> > - up(&info->write_sem);
> > + mutex_unlock(&info->write_mtx);
> > return retval
>
> this code is very very buggy.
more buggy than with the use of a semaphore?
> mutex_lock_interruptible() may not get the mutex in case a signal
> happens... and yet you unlox the mutex unconditionally!!!
as far as i understand only the thread that locked the mutex can
unlock it (as opposed to semaphores, which can be released by any
thread/process). obviously this doesn't make the code be more
correct. what i don't know is how the kernel behaves when
trying to unlock a mutex the thread doesn't own. another and possibly
more important problem of the code is that in case of being
interrupted by a signal the data that should be protected by the
mutex/semaphore can be accessed/changed by two threads at the same
time.
would the following resolve the problem?
if(mutex_lock_interruptible(&info->write_mtx))
return -ERESTARTSYS
thanks for your comments
--
Matthias Kaehlcke
Linux Application Developer
Barcelona
Nothing is more despicable than respect based on fear
(Albert Camus)
.''`.
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