Re: [Adeos-main] [PATCHES] cleanup minor quirks for 1.6-01

[Philippe Gerum <rpm@xenomai.org>]

On Thu, 2006-12-07 at 00:38 +0100, Jan Kiszka wrote:

> > 
> >> If there is actually something to protect, than it should be calling
> >> this proc handler vs. unregistering the domain (and it's proc entry) -
> >> but that is only feasible with something like synchronize_sched, i.e.
> >> waiting a grace period after unregistering so that all handlers are
> >> through. A really uncritical race which exists with a lot of /proc code.
> >>
> > 
> > This race could crash the box, would the descriptor from the
> > unregistered domain belong to a module being unloaded. Since
> > ipipe_register_domain() grabs the critical lock, masking IRQs in
> > the /proc handler would do the trick, but this is a fairly high price to
> > pay for running such a routine. 
> > 
> 
> Better no IRQ lock for this.
> 

Clearly.

> Well, also my synchronize_sched idea is not truly safe (unless the proce
> handler would be called under rcu_read_lock - don't think this is the
> case). I really can't tell how to safely cleanup proc entries that have
> volatile data structures attached. I once asked on LKML for a correct
> pattern but got no reply.

Let's go for a simple mutex excluding the unregistration routine for
now. Not perfect, but still better than the previous situation. It's
been introduced in 1.6-02/x86.

-- 
Philippe.