On Fri, 2016-08-05 at 07:24 -0600, Jan Beulich wrote:
> I'd really like to have those backported, but I have to ask one
> of you to identify which prereq-s are needed on 4.6 and 4.5
> (I'll revert them from 4.5 right away, but I'll wait for an osstest
> flight to confirm the same issue exists on 4.6). 
>
Hey, I could only start working on this this morning (sorry for the
delay), and I'll continue tomorrow but, at least here, staging-4.6
(plus the patches!) crashes like this:

(XEN) [    0.000000] ----[ Xen-4.6.4-pre  x86_64  debug=y  Not tainted ]----
(XEN) [    0.000000] CPU:    0
(XEN) [    0.000000] RIP:    e008:[<ffff82d0801238c4>] _csched_cpu_pick+0x156/0x612
(XEN) [    0.000000] RFLAGS: 0000000000010046   CONTEXT: hypervisor
(XEN) [    0.000000] rax: 0000000000000040   rbx: 0000000000000040   rcx: 0000000000000000
(XEN) [    0.000000] rdx: 000000000000003f   rsi: 0000000000000040   rdi: 0000000000000040
(XEN) [    0.000000] rbp: ffff82d0802f7d68   rsp: ffff82d0802f7c78   r8:  0000000000000000
(XEN) [    0.000000] r9:  0000000000000001   r10: 0000000000000001   r11: 00000000000000b4
(XEN) [    0.000000] r12: 0000000000000040   r13: ffff83032152bf40   r14: ffff82d08033ae40
(XEN) [    0.000000] r15: ffff8300dbdf4000   cr0: 0000000080050033   cr4: 00000000000006e0
(XEN) [    0.000000] cr3: 00000000dba9f000   cr2: 0000000000000000
(XEN) [    0.000000] ds: 0000   es: 0000   fs: 0000   gs: 0000   ss: 0000   cs: e008
(XEN) [    0.000000] Xen stack trace from rsp=ffff82d0802f7c78:
(XEN) [    0.000000]    0000000000000046 0000000200000092 ffff82d08033ae48 ffff82d08028b020
(XEN) [    0.000000]    0000000000000000 ffff82d0802ff040 0000000100000001 ffff82d08033ae40
(XEN) [    0.000000]    0000000000000097 ffff82d0802f7cd8 0000000000000006 ffff82d0802f7ce8
(XEN) [    0.000000]    ffff82d08012d027 ffff830321532000 ffff82d0802f7d28 ffff82d08013c779
(XEN) [    0.000000]    0000000000000000 0000000000000010 0000000000000048 0000000000000048
(XEN) [    0.000000]    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN) [    0.000000]    ffff82d0802f7d78 ffff8300dbdf4000 ffff83032152a000 ffff83032152bf40
(XEN) [    0.000000]    0000000000000000 ffff82d08028e020 ffff82d0802f7d78 ffff82d080123d8e
(XEN) [    0.000000]    ffff82d0802f7db8 ffff82d080123db0 ffff83032152a000 ffff8300dbdf4000
(XEN) [    0.000000]    ffff83032152a000 0000000000000000 0000000000000000 ffff82d08028e020
(XEN) [    0.000000]    ffff82d0802f7de8 ffff82d080129e8d ffff82d0802f7de8 ffff82d08013cda0
(XEN) [    0.000000]    ffff8300dbdf4000 ffff83032152a000 ffff82d0802f7e18 ffff82d080105f59
(XEN) [    0.000000]    ffff82d0802a1720 ffff82d0802a1718 ffff82d0802a1720 ffff82d0802daa60
(XEN) [    0.000000]    ffff82d0802f7e48 ffff82d0802a8145 0000000000000002 ffff83032152b610
(XEN) [    0.000000]    0000000000000002 0000000000000001 ffff82d0802f7f08 ffff82d0802c5c6f
(XEN) [    0.000000]    0000000000000000 0000000000100000 00000000014ae000 0000000000324000
(XEN) [    0.000000]    0080016300000000 0000000300000015 0000000000000000 0000000000000010
(XEN) [    0.000000]    ffff83000008dd50 ffff83000008df20 0000000000000002 ffff83000008dfb0
(XEN) [    0.000000]    0000000800000000 000000010000006e 0000000000000003 00000000000002f8
(XEN) [    0.000000]    0000000000000000 0000000000000000 0000000000000000 0000000000000000
(XEN) [    0.000000] Xen call trace:
(XEN) [    0.000000]    [<ffff82d0801238c4>] _csched_cpu_pick+0x156/0x612
(XEN) [    0.000000]    [<ffff82d080123d8e>] csched_cpu_pick+0xe/0x10
(XEN) [    0.000000]    [<ffff82d080123db0>] csched_vcpu_insert+0x20/0x145
(XEN) [    0.000000]    [<ffff82d080129e8d>] sched_init_vcpu+0x1d1/0x218
(XEN) [    0.000000]    [<ffff82d080105f59>] alloc_vcpu+0x1ba/0x2a4
(XEN) [    0.000000]    [<ffff82d0802a8145>] scheduler_init+0x1b0/0x271
(XEN) [    0.000000]    [<ffff82d0802c5c6f>] __start_xen+0x1f85/0x2550
(XEN) [    0.000000]    [<ffff82d080100073>] __high_start+0x53/0x55
(XEN) [    0.000000] 
(XEN) [    0.000000] 
(XEN) [    0.000000] ****************************************
(XEN) [    0.000000] Panic on CPU 0:
(XEN) [    0.000000] Assertion 'cpu < nr_cpu_ids' failed at ...e/SOURCES/xen/xen.git/xen/include/xen/cpumask.h:97

Which, I think needs at least this hunk (from 6b53bb4ab3c9  "sched:
better handle (not) inserting idle vCPUs in runqueues"):

diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 2beebe8..fddcd52 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -240,20 +240,22 @@ int sched_init_vcpu(struct vcpu *v, unsigned int processor)
     init_timer(&v->poll_timer, poll_timer_fn,
                v, v->processor);
 
-    /* Idle VCPUs are scheduled immediately. */
+    v->sched_priv = SCHED_OP(DOM2OP(d), alloc_vdata, v, d->sched_priv);
+    if ( v->sched_priv == NULL )
+        return 1;
+
+    TRACE_2D(TRC_SCHED_DOM_ADD, v->domain->domain_id, v->vcpu_id);
+
+    /* Idle VCPUs are scheduled immediately, so don't put them in runqueue. */
     if ( is_idle_domain(d) )
     {
         per_cpu(schedule_data, v->processor).curr = v;
         v->is_running = 1;
     }
-
-    TRACE_2D(TRC_SCHED_DOM_ADD, v->domain->domain_id, v->vcpu_id);
-
-    v->sched_priv = SCHED_OP(DOM2OP(d), alloc_vdata, v, d->sched_priv);
-    if ( v->sched_priv == NULL )
-        return 1;
-
-    SCHED_OP(DOM2OP(d), insert_vcpu, v);
+    else
+    {
+        SCHED_OP(DOM2OP(d), insert_vcpu, v);
+    }
 
     return 0;
 }

So, yeah, it's proving a little more complicated than how I thought it
would have, just by looking at the patches. :-/

Will let know.

Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)