WARNING: at /home/konrad/linux-linus/kernel/time/tick-sched.c:935tick_nohz_idle_exit+0x195/0x1b0() on v3.10-rc3
From: Konrad Rzeszutek Wilk
Date: Thu May 30 2013 - 14:30:16 EST
Hello,
I had not yet done a full git bisection run but since this is new code added
in v3.10. I did not see this in v3.9. I think I saw this in v3.10-rc1 but never
got to look at it in depth.
Either way on a PV guest, if I do:
echo 0 > /sys/devices/system/cpu/cpu1/online
echo 1 > /sys/devices/system/cpu/cpu1/online
I get this fat warning:
[ 39.946760] Broke affinity for irq 16
[ 40.071242] installing Xen timer for CPU 1
[ 40.076109] cpu 1 spinlock event irq 48
[ 40.081207] ------------[ cut here ]------------
[ 40.085841] WARNING: at /home/konrad/linux-linus/kernel/time/tick-sched.c:935 tick_nohz_idle_exit+0x195/0x1b0()
[ 40.095970] Modules linked in: dm_multipath dm_mod xen_evtchn iscsi_boot_sysfs iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi libcrc32c crc32c i915 radeon sg sd_mod mperf skge e1000 sata_nv nouveau ata_generic libata fbcon tileblit font bitblit scsi_mod ttm softcursor drm_kms_helper mxm_wmi video wmi xen_blkfront xen_netfront fb_sys_fops sysimgblt sysfillrect syscopyarea xenfs xen_privcmd
[ 40.130893] CPU: 1 PID: 0 Comm: swapper/1 Not tainted 3.10.0-rc3upstream-00068-gdcdbe33 #1
[ 40.139212] Hardware name: BIOSTAR Group N61PB-M2S/N61PB-M2S, BIOS 6.00 PG 09/03/2009
[ 40.147098] ffffffff8193b448 ffff880039da5e60 ffffffff816707c8 ffff880039da5ea0
[ 40.154550] ffffffff8108ce8b ffff880039da4010 ffff88003fa8e500 ffff880039da4010
[ 40.162004] 0000000000000001 ffff880039da4000 ffff880039da4010 ffff880039da5eb0
[ 40.169458] Call Trace:
[ 40.171977] [<ffffffff816707c8>] dump_stack+0x19/0x1b
[ 40.177175] [<ffffffff8108ce8b>] warn_slowpath_common+0x6b/0xa0
[ 40.183243] [<ffffffff8108ced5>] warn_slowpath_null+0x15/0x20
[ 40.189134] [<ffffffff810e4745>] tick_nohz_idle_exit+0x195/0x1b0
[ 40.195287] [<ffffffff810da755>] cpu_startup_entry+0x205/0x250
[ 40.201268] [<ffffffff81661070>] cpu_bringup_and_idle+0x13/0x15
[ 40.207332] ---[ end trace 915c8c486004dda1 ]---
which I presume is b/c the code does not expect to be run _after_ it has
offlined. However, under the PV code, the mechanism is that that a CPU
that has been offlined, can resume (if it is onlined). If you look at:
445 static void __cpuinit xen_play_dead(void) /* used only with HOTPLUG_CPU */
446 {
447 play_dead_common();
448 HYPERVISOR_vcpu_op(VCPUOP_down, smp_processor_id(), NULL);
449 cpu_bringup();
450 }
That is called right after the CPU is put to sleep and the hypercall
VCPUOP_down blocks - until the CPU is brough back up. And which point
we end up calling cpu_bringup - which sets up the clockevets, timers, etc.
I am wondering if part of this is that the ts->inidle gets reset
b/c we end up resetting all the timers but then when xen_play_dead
exits, it ends up right back in the cpu_idle_loop() loop - and we
call tick_nohz_idle_exit().
Thoughts?
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