Hi,
I see the following lockdep splat on my RackMac machine on boot:
[ 6.002593] Registering G5 CPU frequency driver
[ 6.011288] Frequency method: i2c/pfunc, Voltage method: i2c/pfunc
[ 6.023605] Low: 1800 Mhz, High: 2300 Mhz, Cur: 1800 MHz
[ 6.038022] ======================================================
[ 6.042080] windfarm: CPUs control loops started.
[ 6.042084] wf_rm31: Backside control loop started.
[ 6.042086] wf_rm31: Slots control loop started.
[ 6.078644] [ INFO: possible circular locking dependency detected ]
[ 6.091149] 4.1.0-rc6-01265-g908e80d-dirty #15 Not tainted
[ 6.102083] -------------------------------------------------------
[ 6.114586] swapper/0/1 is trying to acquire lock:
[ 6.124136] (&bus->mutex){+.+.+.}, at: [<c00000000004d450>]
.pmac_i2c_open+0x30/0x100
[ 6.139933]
but task is already holding lock:
[ 6.151569] (&policy->rwsem){+.+.+.}, at: [<c000000000620bbc>]
.__cpufreq_add_dev.isra.29+0x34c/0xad0
[ 6.170143]
which lock already depends on the new lock.
[ 6.186464]
the existing dependency chain (in reverse order) is:
[ 6.201401]
-> #4 (&policy->rwsem){+.+.+.}:
[ 6.210077] [<c0000000000d6380>] .lock_acquire+0x80/0x100
[ 6.222061] [<c0000000007a411c>] .down_write+0x6c/0x110
[ 6.233690] [<c000000000620bbc>]
.__cpufreq_add_dev.isra.29+0x34c/0xad0
[ 6.248104] [<c000000000489dd8>] .subsys_interface_register+0xc8/0x120
[ 6.262336] [<c0000000006215f8>] .cpufreq_register_driver+0x138/0x310
[ 6.276404] [<c000000000adeca8>] .g5_cpufreq_init+0x9cc/0xa28
[ 6.289079] [<c00000000000a714>] .do_one_initcall+0xd4/0x270
[ 6.301577] [<c000000000aaa778>] .kernel_init_freeable+0x190/0x270
[ 6.315120] [<c00000000000b17c>] .kernel_init+0x1c/0x120
[ 6.326928] [<c0000000000095b4>] .ret_from_kernel_thread+0x58/0xa4
[ 6.340467]
-> #3 (subsys mutex#2){+.+.+.}:
[ 6.349149] [<c0000000000d6380>] .lock_acquire+0x80/0x100
[ 6.361130] [<c0000000007a0ccc>] .mutex_lock_nested+0xac/0x5a0
[ 6.373980] [<c00000000048aff4>] .bus_probe_device+0x44/0xf0
[ 6.386477] [<c000000000488318>] .device_add+0x508/0x730
[ 6.398284] [<c00000000048fb8c>] .register_cpu+0xfc/0x150
[ 6.410266] [<c000000000aaf27c>] .topology_init+0x108/0x1c0
[ 6.422595] [<c00000000000a714>] .do_one_initcall+0xd4/0x270
[ 6.435092] [<c000000000aaa778>] .kernel_init_freeable+0x190/0x270
[ 6.448637] [<c00000000000b17c>] .kernel_init+0x1c/0x120
[ 6.460444] [<c0000000000095b4>] .ret_from_kernel_thread+0x58/0xa4
[ 6.473983]
-> #2 (cpu_add_remove_lock){+.+.+.}:
[ 6.483536] [<c0000000000d6380>] .lock_acquire+0x80/0x100
[ 6.495517] [<c0000000007a0ccc>] .mutex_lock_nested+0xac/0x5a0
[ 6.508361] [<c0000000000781ac>] .cpu_maps_update_begin+0x1c/0x30
[ 6.521732] [<c000000000070220>] .register_power_pmu+0xa0/0x128
[ 6.534752] [<c000000000abed50>] .init_ppc970_pmu+0x6c/0x8c
[ 6.547081] [<c00000000000a714>] .do_one_initcall+0xd4/0x270
[ 6.559578] [<c000000000aaa698>] .kernel_init_freeable+0xb0/0x270
[ 6.572950] [<c00000000000b17c>] .kernel_init+0x1c/0x120
[ 6.584758] [<c0000000000095b4>] .ret_from_kernel_thread+0x58/0xa4
[ 6.598297]
-> #1 (&host->mutex){+.+.+.}:
[ 6.606633] [<c0000000000d6380>] .lock_acquire+0x80/0x100
[ 6.618615] [<c0000000007a0ccc>] .mutex_lock_nested+0xac/0x5a0
[ 6.631458] [<c00000000004d408>] .kw_i2c_open+0x18/0x30
[ 6.643092] [<c00000000004d4b4>] .pmac_i2c_open+0x94/0x100
[ 6.655247] [<c000000000abb174>] .smp_core99_probe+0x260/0x410
[ 6.668097] [<c000000000ab2f94>] .smp_prepare_cpus+0x1ec/0x220
[ 6.680941] [<c000000000aaa670>] .kernel_init_freeable+0x88/0x270
[ 6.694313] [<c00000000000b17c>] .kernel_init+0x1c/0x120
[ 6.706121] [<c0000000000095b4>] .ret_from_kernel_thread+0x58/0xa4
[ 6.719660]
-> #0 (&bus->mutex){+.+.+.}:
[ 6.727822] [<c0000000000d5304>] .__lock_acquire+0x1194/0x1b70
[ 6.740672] [<c0000000000d6380>] .lock_acquire+0x80/0x100
[ 6.752647] [<c0000000007a0ccc>] .mutex_lock_nested+0xac/0x5a0
[ 6.765497] [<c00000000004d450>] .pmac_i2c_open+0x30/0x100
[ 6.777652] [<c00000000004da34>] .pmac_i2c_do_begin+0x34/0x120
[ 6.790501] [<c0000000000517e0>] .pmf_call_one+0x50/0xd0
[ 6.802302] [<c0000000006265ec>] .g5_pfunc_switch_volt+0x2c/0xc0
[ 6.815501] [<c00000000062659c>] .g5_pfunc_switch_freq+0x1cc/0x1f0
[ 6.829040] [<c0000000006262fc>] .g5_cpufreq_target+0x2c/0x40
[ 6.841716] [<c00000000061de40>] .__cpufreq_driver_target+0x230/0x400
[ 6.855783] [<c000000000622bec>]
.cpufreq_governor_performance+0x3c/0x60
[ 6.870364] [<c00000000061f0d0>] .__cpufreq_governor+0xc0/0x390
[ 6.883389] [<c00000000061f9fc>] .cpufreq_set_policy+0x25c/0x2c0
[ 6.896581] [<c0000000006206d4>] .cpufreq_init_policy+0x84/0xe0
[ 6.909605] [<c0000000006212ec>]
.__cpufreq_add_dev.isra.29+0xa7c/0xad0
[ 6.924013] [<c000000000489dd8>] .subsys_interface_register+0xc8/0x120
[ 6.938253] [<c0000000006215f8>] .cpufreq_register_driver+0x138/0x310
[ 6.952314] [<c000000000adeca8>] .g5_cpufreq_init+0x9cc/0xa28
[ 6.964991] [<c00000000000a714>] .do_one_initcall+0xd4/0x270
[ 6.977488] [<c000000000aaa778>] .kernel_init_freeable+0x190/0x270
[ 6.991033] [<c00000000000b17c>] .kernel_init+0x1c/0x120
[ 7.002841] [<c0000000000095b4>] .ret_from_kernel_thread+0x58/0xa4
[ 7.016380]
other info that might help us debug this:
[ 7.032354] Chain exists of:
&bus->mutex --> subsys mutex#2 --> &policy->rwsem
[ 7.047635] Possible unsafe locking scenario:
[ 7.059439] CPU0 CPU1
[ 7.068467] ---- ----
[ 7.077495] lock(&policy->rwsem);
[ 7.084440] lock(subsys mutex#2);
[ 7.096422] lock(&policy->rwsem);
[ 7.108400] lock(&bus->mutex);
[ 7.114829]
*** DEADLOCK ***
[ 7.126633] 3 locks held by swapper/0/1:
[ 7.134445] #0: (subsys mutex#2){+.+.+.}, at:
[<c000000000489d60>] .subsys_interface_register+0x50/0x120
[ 7.153719] #1: (cpufreq_rwsem){.+.+.+}, at: [<c00000000062093c>]
.__cpufreq_add_dev.isra.29+0xcc/0xad0
[ 7.172817] #2: (&policy->rwsem){+.+.+.}, at:
[<c000000000620bbc>] .__cpufreq_add_dev.isra.29+0x34c/0xad0
[ 7.192261]
stack backtrace:
[ 7.200945] CPU: 1 PID: 1 Comm: swapper/0 Not tainted
4.1.0-rc6-01265-g908e80d-dirty #15
[ 7.217091] Call Trace:
[ 7.221953] [c0000000790beab0] [c0000000007ad48c]
.dump_stack+0x98/0xd4 (unreliable)
[ 7.237407] [c0000000790beb30] [c0000000007a9094]
.print_circular_bug+0x364/0x39c
[ 7.252336] [c0000000790bebe0] [c0000000000d0e40] .check_prev_add+0x8d0/0x8e0
[ 7.266575] [c0000000790becf0] [c0000000000d5304]
.__lock_acquire+0x1194/0x1b70
[ 7.281156] [c0000000790bee20] [c0000000000d6380] .lock_acquire+0x80/0x100
[ 7.294874] [c0000000790beef0] [c0000000007a0ccc]
.mutex_lock_nested+0xac/0x5a0
[ 7.309456] [c0000000790bf010] [c00000000004d450] .pmac_i2c_open+0x30/0x100
[ 7.323349] [c0000000790bf0a0] [c00000000004da34]
.pmac_i2c_do_begin+0x34/0x120
[ 7.337931] [c0000000790bf130] [c0000000000517e0] .pmf_call_one+0x50/0xd0
[ 7.351477] [c0000000790bf1c0] [c0000000006265ec]
.g5_pfunc_switch_volt+0x2c/0xc0
[ 7.366405] [c0000000790bf230] [c00000000062659c]
.g5_pfunc_switch_freq+0x1cc/0x1f0
[ 7.381688] [c0000000790bf300] [c0000000006262fc]
.g5_cpufreq_target+0x2c/0x40
[ 7.396096] [c0000000790bf370] [c00000000061de40]
.__cpufreq_driver_target+0x230/0x400
[ 7.411893] [c0000000790bf430] [c000000000622bec]
.cpufreq_governor_performance+0x3c/0x60
[ 7.428219] [c0000000790bf4a0] [c00000000061f0d0]
.__cpufreq_governor+0xc0/0x390
[ 7.442975] [c0000000790bf530] [c00000000061f9fc]
.cpufreq_set_policy+0x25c/0x2c0
[ 7.457904] [c0000000790bf5c0] [c0000000006206d4]
.cpufreq_init_policy+0x84/0xe0
[ 7.472666] [c0000000790bf920] [c0000000006212ec]
.__cpufreq_add_dev.isra.29+0xa7c/0xad0
[ 7.488810] [c0000000790bfa10] [c000000000489dd8]
.subsys_interface_register+0xc8/0x120
[ 7.504782] [c0000000790bfab0] [c0000000006215f8]
.cpufreq_register_driver+0x138/0x310
[ 7.520586] [c0000000790bfb50] [c000000000adeca8]
.g5_cpufreq_init+0x9cc/0xa28
[ 7.534993] [c0000000790bfc10] [c00000000000a714] .do_one_initcall+0xd4/0x270
[ 7.549233] [c0000000790bfd00] [c000000000aaa778]
.kernel_init_freeable+0x190/0x270
[ 7.564510] [c0000000790bfdb0] [c00000000000b17c] .kernel_init+0x1c/0x120
[ 7.578056] [c0000000790bfe30] [c0000000000095b4]
.ret_from_kernel_thread+0x58/0xa4
Thanks.
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