Re: kern/38637: pppoe fails to reconnect sometimes

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Fri, Apr 03, 2009 at 08:06:00PM +0200, Manuel Bouyer wrote:
> On Thu, Oct 02, 2008 at 10:50:05AM +0000, Martin Husemann wrote:
> >  Sorry, I don't see how this could happen besides the softint handling
> >  breaking completely (something corrupting the call wheel?):
> > [...]
> 
> Update on this: this time (with a 5.0_RC3 kernel), it's not the ppoeinq
> which stopped being processed and did overflow, but ipintrq !
> So it's really related to soft interrupt not being called anymore ...

I think I found the reason for this (or at last a possible reason).
In sys/kern/kern_softint.c, sh_flags should be declared volatile.
Without it, on ports where splhigh() is inline, the compiler will optimise
the second SOFTINT_PENDING test in softint_schedule(). A dissasembly
of softint_schedule() with and without the volatile sh_flags confirm this
on sparc.
Because of this there is a race that could lead to the softhand_t
being enqueued twice on si_q, leading to a corrupted queue and
some handler being SOFTINT_PENDING but never called.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--