Date: Sun, 23 Jun 2002 21:34:43 -0500 From: Jonathan Lemon <jlemon@flugsvamp.com> To: Julian Elischer <julian@elischer.org> Cc: Jonathan Lemon <jlemon@flugsvamp.com>, dillon@apollo.backplane.com, hackers@freebsd.org Subject: Re: Bug in wakeup() (stable and current) ? Message-ID: <20020623213443.K91821@prism.flugsvamp.com> In-Reply-To: <Pine.BSF.4.21.0206231840270.44896-100000@InterJet.elischer.org> References: <200206232158.g5NLw9c49030@prism.flugsvamp.com> <Pine.BSF.4.21.0206231840270.44896-100000@InterJet.elischer.org>
next in thread | previous in thread | raw e-mail | index | archive | help
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);
To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20020623213443.K91821>