Re: 8139too termination

[Andrew Morton <akpm@zip.com.au>]

Robert Kuebel wrote:
> 
> hi,
> 
> i have been getting this message at shutdown ...
> 
> "eth1: unable to signal thread"
> 
> it turns out that 8139too's kernel thread gets killed at shutdown (or
> reboot) when SIGTERM is sent to all processes.  then the network
> shutdown script comes along and takes down the interface.  the driver
> complains ...
> 
> "eth1: unable to signal thread"
> 
> because the thread has already terminated.  the driver currently does
> not block any signals.
> 
> my question is, should 8139too really not block any signals (and allow
> itself to be killed by them)?  isn't it a bad thing to allow a kernel
> thread to be killed accidentally like this?
> 

Yes, I'd agree that the driver should ignore random signals.
The kernel thread should only allow itself to be terminated
via the driver's close() method.

An obvious approach is to change rtl8139_close() to do:

	tp->diediedie = 1;
	wmb();
	ret = kill_proc(...);

and test the flag in rtl8139_thread().

The tricky part is teaching the thread to ignore the
spurious signals - the signal_pending() state needs to be
cleared.  I think flush_signals() is the way to do this.
See context_thread() for an example.

           spin_lock_irq(&curtask->sigmask_lock);
           flush_signals(curtask);
           recalc_sigpending(curtask);
           spin_unlock_irq(&curtask->sigmask_lock);

The recalc_sigpending() here appears to be unnecessary...

The kernel thread in 8139too has certainly been an interesting
learning exercise :)  Using signals and task management in-kernel
is full of pitfalls.  In retrospect, probably it should have used
waitqueues directly.

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