ondemand vs suspend.

[Dave Jones <davej@redhat.com>]

Here's a puzzling case that Peter stumbled across when experimenting
with suspend on one of the new dual-core Intel-based Mac Mini's.

The hibernate process would just lock up, and never shut down.

 4190 ?        S<     0:00  \_ [kstopmachine]
 4191 ?        Z<     0:00      \_ [kstopmachine] <defunct>
  
dmesg showed that we had offlined the 2nd core..

PM: suspend-to-disk mode set to 'platform'
Freezing cpus ...
Breaking affinity for irq 0
Breaking affinity for irq 14
Breaking affinity for irq 217
Breaking affinity for irq 225
CPU 1 is now offline
SMP alternatives: switching to UP code

and sysrq-t showed that we were erm.. spinning.

ondemand      D EDDD1300  3452  1462     11          2160  1345 (L-TLB)
       f7f8eec0 f7f8eef4 f7f8eef4 eddd1300 003d10ba c05a4c2c 0000000a f7eb4fcc
       f7eb4eb0 c06e0c00 c19c4860 eddd1300 003d10ba 00000000 00000000 00000000
       f7f8eedc c041fc12 00000296 ffffffff f7f8eef4 00000246 00000246 c06e65d8
Call Trace:
 <c0607f89> __down+0x131/0x14a  <c0605432> __down_failed+0xa/0x10
 <c043aa55> .text.lock.cpu+0x2b/0x32  <c043a7ad> lock_cpu_hotplug+0xa/0xc
 <c05a3dae> __cpufreq_driver_target+0x15/0x6d  <f8bce3da> do_dbs_timer+0x229/0x287 [cpufreq_ondemand]
 <c04321fb> run_workqueue+0x81/0xc0  <c0432c35> worker_thread+0xce/0x101
 <c0435353> kthread+0xa3/0xd0  <c0402005> kernel_thread_helper+0x5/0xb
pm-hibernate  D F395EB00  1816  3934   2495                     (NOTLB)
       e632ade8 c0465c6c 00000004 f395eb00 003d10ba f2c31800 00000007 ddc7e44c
       ddc7e330 c1b1b190 c19c4860 f395eb00 003d10ba 00000000 00000000 c0481c9c
       f8bcfa40 f8bcfa40 e632a000 e632adf8 00000000 c0438ad8 f8bce646 f8bcfa54
Call Trace:
 <c06075ba> __mutex_lock_slowpath+0x19b/0x3e3  <c0607826> mutex_lock+0x24/0x27
 <f8bce646> cpufreq_governor_dbs+0x20e/0x2b0 [cpufreq_ondemand]  <c05a385f> __cpufreq_governor+0x57/0xd8
 <c05a4106> cpufreq_remove_dev+0x197/0x208  <c05a4716> cpufreq_cpu_callback+0x49/0x52
 <c0609795> notifier_call_chain+0x18/0x29  <c042f9da> blocking_notifier_call_chain+0x37/0x4f
 <c043a98d> cpu_down+0x12b/0x1c8  <c04420b0> disable_nonboot_cpus+0x35/0xa1
 <c043fc93> prepare_processes+0x13/0x3b  <c043fedd> pm_suspend_disk+0x9/0xf3
 <c043eead> enter_state+0x53/0x1c1  <c043f0a1> state_store+0x86/0x9c
 <c04a4d14> subsys_attr_store+0x20/0x25  <c04a4e18> sysfs_write_file+0xab/0xd1
 <c046b25c> vfs_write+0xab/0x154  <c046b890> sys_write+0x3b/0x60
 <c060837f> syscall_call+0x7/0xb
kstopmachine  S ED25F800  3428  4190     11  4191          2160 (L-TLB)
       dc184fac c19c4860 c04f473a ed25f800 003d10ba c041115b 00000003 f7e38e4c
       f7e38d30 c1acf050 c19cc860 ed25f800 003d10ba 00000000 00000001 00000246
       e632ae94 dc184f90 00000246 e632ae90 00000000 c041ee49 00000000 00000000
Call Trace:
 <c044579f> do_stop+0xf9/0x129  <c0435353> kthread+0xa3/0xd0
 <c0402005> kernel_thread_helper+0x5/0xb
kstopmachine  X ED25F800  3736  4191   4190                     (L-TLB)
       f7ecefb4 c0605fda f7ecef78 ed25f800 003d10ba 003d10ba 00000002 f2e622cc
       f2e621b0 ddc7e330 c19c4860 ed25f800 003d10ba 00000000 00000000 00000000
       f7ecef94 00000202 00000202 f2ec1ad8 00000000 c0608093 f7ecefb4 00000202
Call Trace:
 <c0427428> do_exit+0x7a1/0x7ab  <c040200b> kernel_thread_helper_end+0x0/0xe

D    pm-hibernate: 3934 [ddc7e330, 118] blocked on mutex: [f8bcfa40] {dbs_mutex}
.. held by:          ondemand: 1462 [f7eb4eb0, 110]
... acquired at:               do_dbs_timer+0x13/0x287 [cpufreq_ondemand]


This doesn't happen if the govenor is 'userspace', so I'm wondering if
we're doing something silly in ondemand when we've offlined a CPU.

Any ideas ?

		Dave

-- 
http://www.codemonkey.org.uk