[111/141] xen/smp: Fixup NOHZ per cpu data when onlining an offline CPU.

Steven Rostedt
2013-07-03T19:12:55Z

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3.6.11.6 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

[ Upstream commit 466318a87f28cb3ba0d08a3b7ef1a37ae73d5aa7 ]

The xen_play_dead is an undead function. When the vCPU is told to
offline it ends up calling xen_play_dead wherin it calls the
VCPUOP_down hypercall which offlines the vCPU. However, when the
vCPU is onlined back, it resumes execution right after
VCPUOP_down hypercall.

That was OK (albeit the API for play_dead assumes that the CPU
stays dead and never returns) but with commit 4b0c0f294
(tick: Cleanup NOHZ per cpu data on cpu down) that is no longer safe
as said commit resets the ts->inidle which at the start of the
cpu_idle loop was set.

The net effect is that we get this warn:

Broke affinity for irq 16
installing Xen timer for CPU 1
cpu 1 spinlock event irq 48
------------[ cut here ]------------
WARNING: at /home/konrad/linux-linus/kernel/time/tick-sched.c:935 tick_nohz_idle_exit+0x195/0x1b0()
Modules linked in: dm_multipath dm_mod xen_evtchn iscsi_boot_sysfs
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.10.0-rc3upstream-00068-gdcdbe33 #1
Hardware name: BIOSTAR Group N61PB-M2S/N61PB-M2S, BIOS 6.00 PG 09/03/2009
ffffffff8193b448 ffff880039da5e60 ffffffff816707c8 ffff880039da5ea0
ffffffff8108ce8b ffff880039da4010 ffff88003fa8e500 ffff880039da4010
0000000000000001 ffff880039da4000 ffff880039da4010 ffff880039da5eb0
Call Trace:
[<ffffffff816707c8>] dump_stack+0x19/0x1b
[<ffffffff8108ce8b>] warn_slowpath_common+0x6b/0xa0
[<ffffffff8108ced5>] warn_slowpath_null+0x15/0x20
[<ffffffff810e4745>] tick_nohz_idle_exit+0x195/0x1b0
[<ffffffff810da755>] cpu_startup_entry+0x205/0x250
[<ffffffff81661070>] cpu_bringup_and_idle+0x13/0x15
---[ end trace 915c8c486004dda1 ]---

b/c ts_inidle is set to zero. Thomas suggested that we just add a workaround
to call tick_nohz_idle_enter before returning from xen_play_dead() - and
that is what this patch does and fixes the issue.

We also add the stable part b/c git commit 4b0c0f294 is on the stable
tree.

CC: stable@vger.kernel.org
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/x86/xen/smp.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 641c91e..76bce6e 100644
--- a/arch/x86/xen/smp.c
+++ b/arch/x86/xen/smp.c
@@ -17,6 +17,7 @@
#include <linux/slab.h>
#include <linux/smp.h>
#include <linux/irq_work.h>
+#include <linux/tick.h>

#include <asm/paravirt.h>
#include <asm/desc.h>
@@ -435,6 +436,13 @@ static void __cpuinit xen_play_dead(void) /* used only with HOTPLUG_CPU */
HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
cpu_bringup();
/*
+ * commit 4b0c0f294 (tick: Cleanup NOHZ per cpu data on cpu down)
+ * clears certain data that the cpu_idle loop (which called us
+ * and that we return from) expects. The only way to get that
+ * data back is to call:
+ */
+ tick_nohz_idle_enter();
+ /*
* Balance out the preempt calls - as we are running in cpu_idle
* loop which has been called at bootup from cpu_bringup_and_idle.
* The cpucpu_bringup_and_idle called cpu_bringup which made a
--
1.7.10.4