Date: Sun, 23 Jun 2002 20:34:33 -0700 (PDT) From: Julian Elischer <julian@elischer.org> To: Jonathan Lemon <jlemon@flugsvamp.com> Cc: dillon@apollo.backplane.com, hackers@freebsd.org Subject: Re: Bug in wakeup() (stable and current) ? Message-ID: <Pine.BSF.4.21.0206232023540.44896-100000@InterJet.elischer.org> In-Reply-To: <20020623213443.K91821@prism.flugsvamp.com>
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yep
Matt added a similar patch to the KSE branch...
the debug stuff I added to TAILQ
adds (when compiled in) info on the last 2 places to to linkage
operations..
it also initialises the pointers on elements to -1
it's great for helping find places that are screwing up linkages
e.g. in the KSE run queues which are quite complicated :-)
On Sun, 23 Jun 2002, Jonathan Lemon wrote:
> On Sun, Jun 23, 2002 at 06:42:43PM -0700, Julian Elischer wrote:
> >
> > On Sun, 23 Jun 2002, Jonathan Lemon wrote:
> > > The code works simply because it relies TAILQ_REMOVE() not changing
> > > the tqe_next pointer. I suppose that this should either be documented,
> > > or the loop changed back to use a temp variable:
> > >
> > > for (td = TAILQ_FIRST(qp); td != NULL; td = tdq) {
> > > tdq = TAILQ_NEXT(td, td_slpq);
> > > ...
> > > }
> >
> > I just added debug code in the TAILQ code that sets the forward pointor
> > to -1. Since Matt had this it's possible that this is what hit him?
>
> Most definitely. If you reset tqe_next, the code stops working. Try
> the patch below.
> --
> Jonathan
>
>
> Index: kern_synch.c
> ===================================================================
> RCS file: /ncvs/src/sys/kern/kern_synch.c,v
> retrieving revision 1.175
> diff -u -r1.175 kern_synch.c
> --- kern_synch.c 7 Jun 2002 05:39:16 -0000 1.175
> +++ kern_synch.c 24 Jun 2002 02:42:40 -0000
> @@ -605,13 +605,14 @@
> register void *ident;
> {
> register struct slpquehead *qp;
> - register struct thread *td;
> + register struct thread *td, *tdn;
> struct proc *p;
>
> mtx_lock_spin(&sched_lock);
> qp = &slpque[LOOKUP(ident)];
> restart:
> - TAILQ_FOREACH(td, qp, td_slpq) {
> + for (td = TAILQ_FIRST(qp); td != NULL; td = tdn) {
> + tdn = TAILQ_NEXT(td, td_slpq);
> p = td->td_proc;
> if (td->td_wchan == ident) {
> TAILQ_REMOVE(qp, td, td_slpq);
>
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