Date: Wed, 29 Sep 2004 16:26:16 -0400 From: Stephan Uphoff <ups@tree.com> To: Peter Holm <peter@holm.cc> Cc: "freebsd-arch@freebsd.org" <freebsd-arch@freebsd.org> Subject: Re: scheduler (sched_4bsd) questions Message-ID: <1096489576.3733.1868.camel@palm.tree.com> In-Reply-To: <1096477932.3733.1471.camel@palm.tree.com> References: <1095468747.31297.241.camel@palm.tree.com> <1095529353.31297.1192.camel@palm.tree.com> <1096135220.53798.17754.camel@palm.tree.com> <20040926075218.GA85983@peter.osted.lan> <1096339936.3733.279.camel@palm.tree.com> <20040928074926.GA99957@peter.osted.lan> <1096383103.3733.312.camel@palm.tree.com> <20040929085748.GA19695@peter.osted.lan> <1096467843.3733.1145.camel@palm.tree.com> <1096477932.3733.1471.camel@palm.tree.com>
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Forgot to attach the patch ...
Stephan
On Wed, 2004-09-29 at 13:12, Stephan Uphoff wrote:
> On Wed, 2004-09-29 at 10:24, Stephan Uphoff wrote:
> > On Wed, 2004-09-29 at 04:57, Peter Holm wrote:
> > > It's hard for me to tell if your patch has made any difference.
> > > The freeze is still there. I'll try to make the same test once more
> > > without your patches to see if I get the same pattern in freezes.
> >
> > I found some problems yesterday with mutex priority inheritance that
> > could potentially cause your freeze patterns.
> >
> > I will try to roll a preliminary patch as soon as the caffeine does its
> > magic.
>
> OK - here is a crude patch to fix some problems with mutex priority
> inheritance. My theory is that the clock thread gets stuck waiting on
> GIANT.
>
> During release/acquisition of a contested sleep mutex there are a few
> windows where a task can be preempted when actions (waking up blocked
> threads, ownership of the mutex, ..) need to be atomic as far as
> scheduling is concerned. Otherwise priority inheritance may fail. The
> patch uses critical_enter/critical_exit to protect these regions against
> preemption.
>
> It would be great if could run this in addition to the other patches.
>
> Stephan
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Index: kern_mutex.c
===================================================================
RCS file: /cvsroot/src/sys/kern/kern_mutex.c,v
retrieving revision 1.149
diff -u -r1.149 kern_mutex.c
--- kern_mutex.c 2 Sep 2004 18:59:15 -0000 1.149
+++ kern_mutex.c 29 Sep 2004 16:50:36 -0000
@@ -492,7 +492,9 @@
if (v == MTX_CONTESTED) {
MPASS(ts != NULL);
m->mtx_lock = (uintptr_t)td | MTX_CONTESTED;
+ critical_enter();
turnstile_claim(ts);
+ critical_exit();
break;
}
#endif
@@ -651,6 +653,9 @@
#else
MPASS(ts != NULL);
#endif
+
+ critical_enter();
+
#ifndef PREEMPTION
/* XXX */
td1 = turnstile_head(ts);
@@ -671,6 +676,7 @@
}
#endif
turnstile_unpend(ts);
+ critical_exit();
#ifndef PREEMPTION
/*
--=-MHoXvfgwm/AM79gvF4x9--
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