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Date:      Wed, 6 Apr 2011 13:08:20 -0400
From:      Ryan Stone <rysto32@gmail.com>
To:        freebsd-current@freebsd.org
Subject:   Re: sched_4bsd startup crash trying to run a bound thread on an AP that hasn't started
Message-ID:  <BANLkTinvisvGiQOs5w-nsxzRVbJUN5%2B5yQ@mail.gmail.com>
In-Reply-To: <201104060836.56542.jhb@freebsd.org>
References:  <BANLkTinSyDaY-06N95n8c1NxOSdEnb5FkQ@mail.gmail.com> <201104060836.56542.jhb@freebsd.org>
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On Wed, Apr 6, 2011 at 8:36 AM, John Baldwin <jhb@freebsd.org> wrote:
> Hummm. =A0Patching 4BSD to use the same route as ULE may be the best solu=
tion
> for now if that is easiest. =A0Alternatively, you could change 4BSD's
> sched_add() to not try to kick other CPUs until smp_started is true.

At first I thought that it was a consequence of the way it does CPU
affinity, but now I see that it shortcuts if smp_started is not true.
How about something like the following for 4BSD?

--- sched_4bsd.c        (revision 220222)
+++ sched_4bsd.c        (working copy)
@@ -1242,14 +1242,14 @@
        }
        TD_SET_RUNQ(td);

-       if (td->td_pinned !=3D 0) {
+       if (smp_started && td->td_pinned !=3D 0) {
                cpu =3D td->td_lastcpu;
                ts->ts_runq =3D &runq_pcpu[cpu];
                single_cpu =3D 1;
                CTR3(KTR_RUNQ,
                    "sched_add: Put td_sched:%p(td:%p) on cpu%d runq", ts, =
td,
                    cpu);
-       } else if (td->td_flags & TDF_BOUND) {
+       } else if (smp_started && (td->td_flags & TDF_BOUND)) {
                /* Find CPU from bound runq. */
                KASSERT(SKE_RUNQ_PCPU(ts),
                    ("sched_add: bound td_sched not on cpu runq"));
@@ -1258,7 +1258,7 @@
                CTR3(KTR_RUNQ,
                    "sched_add: Put td_sched:%p(td:%p) on cpu%d runq", ts, =
td,
                    cpu);
-       } else if (ts->ts_flags & TSF_AFFINITY) {
+       } else if (smp_started && (ts->ts_flags & TSF_AFFINITY)) {
                /* Find a valid CPU for our cpuset */
                cpu =3D sched_pickcpu(td);
                ts->ts_runq =3D &runq_pcpu[cpu];

The flow control is a bit awkward because of the multiple
affinity/bound cpu cases.  If somebody prefers the code to be
structured differently I'd be open to suggestions.

Ryan

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