| From 466318a87f28cb3ba0d08a3b7ef1a37ae73d5aa7 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. |
| |
| From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> |
| |
| 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> |
| |
| --- |
| arch/x86/xen/smp.c | 8 ++++++++ |
| 1 file changed, 8 insertions(+) |
| |
| --- 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> |
| @@ -436,6 +437,13 @@ static void __cpuinit xen_play_dead(void |
| 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 */ |
