Re: kern/38637: pppoe fails to reconnect sometimes

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

The following reply was made to PR kern/38637; it has been noted by GNATS.

From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
To: gnats-bugs%NetBSD.org@localhost
Cc: kern-bug-people%NetBSD.org@localhost, gnats-admin%NetBSD.org@localhost, 
netbsd-bugs%NetBSD.org@localhost
Subject: Re: kern/38637: pppoe fails to reconnect sometimes
Date: Tue, 5 May 2009 22:20:21 +0200

 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
 --