Patchwork [3.8.y.z,extended,stable] Patch "xen/smp: Fixup NOHZ per cpu data when onlining an offline CPU." has been added to staging queue

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Submitter Kamal Mostafa
Date June 11, 2013, 8:01 p.m.
Message ID <1370980885-30893-1-git-send-email-kamal@canonical.com>
Download mbox | patch
Permalink /patch/250630/
State New
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Comments

Kamal Mostafa - June 11, 2013, 8:01 p.m.
This is a note to let you know that I have just added a patch titled

    xen/smp: Fixup NOHZ per cpu data when onlining an offline CPU.

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.3.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

From b436531f2149fc81da460e391f0990d788f5f0ec Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Date: Mon, 3 Jun 2013 10:33:55 -0400
Subject: xen/smp: Fixup NOHZ per cpu data when onlining an offline CPU.

commit 466318a87f28cb3ba0d08a3b7ef1a37ae73d5aa7 upstream.

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.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 arch/x86/xen/smp.c | 8 ++++++++
 1 file changed, 8 insertions(+)

--
1.8.1.2

Patch

diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c
index 48d7b2c..5f8e4fb 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>
@@ -432,6 +433,13 @@  static void __cpuinit xen_play_dead(void) /* used only with HOTPLUG_CPU */
 	play_dead_common();
 	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();
 }

 #else /* !CONFIG_HOTPLUG_CPU */