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| author | Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> | 2012-02-01 15:56:54 -0500 |
|---|---|---|
| committer | Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> | 2012-02-03 16:05:42 -0500 |
| commit | 41bd956de3dfdc3a43708fe2e0c8096c69064a1e (patch) | |
| tree | 1a2a31181c6c89dd754c46376fd82b3e0ba77e5e | |
| parent | 5b02aa1e6e7cf7d3bbf8027dc7e05e0eb2f1e828 (diff) | |
| download | op-kernel-dev-41bd956de3dfdc3a43708fe2e0c8096c69064a1e.zip op-kernel-dev-41bd956de3dfdc3a43708fe2e0c8096c69064a1e.tar.gz | |
xen/smp: Fix CPU online/offline bug triggering a BUG: scheduling while atomic.
When a user offlines a VCPU and then onlines it, we get:
NMI watchdog disabled (cpu2): hardware events not enabled
BUG: scheduling while atomic: swapper/2/0/0x00000002
Modules linked in: dm_multipath dm_mod xen_evtchn iscsi_boot_sysfs iscsi_tcp libiscsi_tcp libiscsi scsi_transport_iscsi scsi_mod libcrc32c crc32c radeon fbco
ttm bitblit softcursor drm_kms_helper xen_blkfront xen_netfront xen_fbfront fb_sys_fops sysimgblt sysfillrect syscopyarea xen_kbdfront xenfs [last unloaded:
Pid: 0, comm: swapper/2 Tainted: G O 3.2.0phase15.1-00003-gd6f7f5b-dirty #4
Call Trace:
[<ffffffff81070571>] __schedule_bug+0x61/0x70
[<ffffffff8158eb78>] __schedule+0x798/0x850
[<ffffffff8158ed6a>] schedule+0x3a/0x50
[<ffffffff810349be>] cpu_idle+0xbe/0xe0
[<ffffffff81583599>] cpu_bringup_and_idle+0xe/0x10
The reason for this should be obvious from this call-chain:
cpu_bringup_and_idle:
\- cpu_bringup
| \-[preempt_disable]
|
|- cpu_idle
\- play_dead [assuming the user offlined the VCPU]
| \
| +- (xen_play_dead)
| \- HYPERVISOR_VCPU_off [so VCPU is dead, once user
| | onlines it starts from here]
| \- cpu_bringup [preempt_disable]
|
+- preempt_enable_no_reschedule()
+- schedule()
\- preempt_enable()
So we have two preempt_disble() and one preempt_enable(). Calling
preempt_enable() after the cpu_bringup() in the xen_play_dead
fixes the imbalance.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
| -rw-r--r-- | arch/x86/xen/smp.c | 7 |
1 files changed, 7 insertions, 0 deletions
diff --git a/arch/x86/xen/smp.c b/arch/x86/xen/smp.c index 041d4fe..501d4e0 100644 --- a/arch/x86/xen/smp.c +++ b/arch/x86/xen/smp.c @@ -409,6 +409,13 @@ 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(); + /* + * 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 + * preempt_disable() So this preempt_enable will balance it out. + */ + preempt_enable(); } #else /* !CONFIG_HOTPLUG_CPU */ |
