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SubjectRe: potential deadlock in cpufreq-dt
Hi all,

[since Jiada's initial report was based on 4.14.50+]
FWIW, I can consistently reproduce this lockdep issue on 4.18.0-rc6:

[ 17.119559] ======================================================
[ 17.119571] WARNING: possible circular locking dependency detected
[ 17.119589] 4.18.0-rc6 #3 Not tainted
[ 17.119601] ------------------------------------------------------
[ 17.119617] systemd-udevd/1538 is trying to acquire lock:
[ 17.119631] (____ptrval____) (&sb->s_type->i_mutex_key
[ 17.137496] #3){+.+.}, at: start_creating+0xbc/0x140
[ 17.137573]
[ 17.137573] but task is already holding lock:
[ 17.137597] (____ptrval____) (opp_table_lock){+.+.}, at: dev_pm_opp_get_opp_table+0xac/0x310
[ 17.181185]
[ 17.181185] which lock already depends on the new lock.
[ 17.189506]
[ 17.189506] the existing dependency chain (in reverse order) is:
[ 17.197116]
[ 17.197116] -> #3 (opp_table_lock){+.+.}:
[ 17.202803] lock_acquire+0x578/0x5c0
[ 17.207101] __mutex_lock+0xec/0xdf8
[ 17.211309] mutex_lock_nested+0x3c/0x4c
[ 17.215866] dev_pm_opp_get_opp_table+0xac/0x310
[ 17.221121] dev_pm_opp_set_regulators+0x38/0x300
[ 17.226506] cpufreq_init+0x198/0x3e0 [cpufreq_dt]
[ 17.231950] cpufreq_online+0x3f0/0xcd4
[ 17.236425] cpufreq_add_dev+0x164/0x17c
[ 17.240988] subsys_interface_register+0x244/0x264
[ 17.246409] cpufreq_register_driver+0x178/0x278
[ 17.251680] dt_cpufreq_probe+0x158/0x178 [cpufreq_dt]
[ 17.257435] platform_drv_probe+0xa4/0x134
[ 17.262167] driver_probe_device+0x36c/0x488
[ 17.267085] __driver_attach+0x150/0x1e4
[ 17.271642] bus_for_each_dev+0x110/0x138
[ 17.271677] driver_attach+0x50/0x5c
[ 17.281065] bus_add_driver+0x2ac/0x2f8
[ 17.281093] driver_register+0x180/0x1c8
[ 17.281124] __platform_driver_register+0x9c/0xac
[ 17.289056] dt_cpufreq_platdrv_init+0x28/0x1000 [cpufreq_dt]
[ 17.289093] do_one_initcall+0x59c/0xab0
[ 17.298045] do_init_module+0x174/0x450
[ 17.298073] load_module+0x3a40/0x3b60
[ 17.298101] sys_finit_module+0x150/0x168
[ 17.309161] el0_svc_naked+0x30/0x34
[ 17.309176]
[ 17.309176] -> #2 (
[ 17.325197] subsys mutex#6){+.+.}:
[ 17.334020] lock_acquire+0x578/0x5c0
[ 17.334048] __mutex_lock+0xec/0xdf8
[ 17.334069] mutex_lock_nested+0x3c/0x4c
[ 17.375822] subsys_interface_register+0x10c/0x264
[ 17.381268] cpufreq_register_driver+0x178/0x278
[ 17.386563] dt_cpufreq_probe+0x158/0x178 [cpufreq_dt]
[ 17.392355] platform_drv_probe+0xa4/0x134
[ 17.397089] driver_probe_device+0x36c/0x488
[ 17.402001] __driver_attach+0x150/0x1e4
[ 17.406556] bus_for_each_dev+0x110/0x138
[ 17.411202] driver_attach+0x50/0x5c
[ 17.415409] bus_add_driver+0x2ac/0x2f8
[ 17.419881] driver_register+0x180/0x1c8
[ 17.424442] __platform_driver_register+0x9c/0xac
[ 17.429825] dt_cpufreq_platdrv_init+0x28/0x1000 [cpufreq_dt]
[ 17.436234] do_one_initcall+0x59c/0xab0
[ 17.440799] do_init_module+0x174/0x450
[ 17.445243] load_module+0x3a40/0x3b60
[ 17.449588] sys_finit_module+0x150/0x168
[ 17.454193] el0_svc_naked+0x30/0x34
[ 17.458350]
[ 17.458350] -> #1 (cpu_hotplug_lock.rw_sem){++++}:
[ 17.464779] lock_acquire+0x578/0x5c0
[ 17.469033] cpus_read_lock+0x60/0x130
[ 17.473379] static_key_enable+0x1c/0x34
[ 17.477894] sched_feat_write+0x300/0x3ec
[ 17.482501] full_proxy_write+0xa4/0xc8
[ 17.486935] __vfs_write+0x10c/0x368
[ 17.491100] vfs_write+0x144/0x2e8
[ 17.495090] ksys_write+0xcc/0x13c
[ 17.499079] sys_write+0x34/0x44
[ 17.502892] el0_svc_naked+0x30/0x34
[ 17.507046]
[ 17.507046] -> #0 (&sb->s_type->i_mutex_key#3){+.+.}:
[ 17.513742] __lock_acquire+0x1968/0x1f4c
[ 17.518348] lock_acquire+0x578/0x5c0
[ 17.522606] down_write+0xb8/0x148
[ 17.526602] start_creating+0xbc/0x140
[ 17.530948] debugfs_create_dir+0x2c/0x1b0
[ 17.535642] opp_debug_register+0xc4/0x10c
[ 17.540330] _add_opp_dev+0x178/0x1d8
[ 17.544581] dev_pm_opp_get_opp_table+0x134/0x310
[ 17.549885] dev_pm_opp_set_regulators+0x38/0x300
[ 17.555224] cpufreq_init+0x198/0x3e0 [cpufreq_dt]
[ 17.560622] cpufreq_online+0x3f0/0xcd4
[ 17.565052] cpufreq_add_dev+0x164/0x17c
[ 17.569574] subsys_interface_register+0x244/0x264
[ 17.574968] cpufreq_register_driver+0x178/0x278
[ 17.580211] dt_cpufreq_probe+0x158/0x178 [cpufreq_dt]
[ 17.585953] platform_drv_probe+0xa4/0x134
[ 17.590647] driver_probe_device+0x36c/0x488
[ 17.595517] __driver_attach+0x150/0x1e4
[ 17.600034] bus_for_each_dev+0x110/0x138
[ 17.604640] driver_attach+0x50/0x5c
[ 17.608808] bus_add_driver+0x2ac/0x2f8
[ 17.613240] driver_register+0x180/0x1c8
[ 17.617761] __platform_driver_register+0x9c/0xac
[ 17.623092] dt_cpufreq_platdrv_init+0x28/0x1000 [cpufreq_dt]
[ 17.629449] do_one_initcall+0x59c/0xab0
[ 17.633970] do_init_module+0x174/0x450
[ 17.638402] load_module+0x3a40/0x3b60
[ 17.642747] sys_finit_module+0x150/0x168
[ 17.647350] el0_svc_naked+0x30/0x34
[ 17.651506]
[ 17.651506] other info that might help us debug this:
[ 17.651506]
[ 17.659624] Chain exists of:
[ 17.659624] &sb->s_type->i_mutex_key#3 --> subsys mutex#6 --> opp_table_lock
[ 17.659624]
[ 17.671440] Possible unsafe locking scenario:
[ 17.671440]
[ 17.677445] CPU0 CPU1
[ 17.682039] ---- ----
[ 17.686631] lock(opp_table_lock);
[ 17.690197] lock(subsys mutex#6);
[ 17.696315] lock(opp_table_lock);
[ 17.702421] lock(&sb->s_type->i_mutex_key#3);
[ 17.707051]
[ 17.707051] *** DEADLOCK ***
[ 17.707051]
[ 17.713070] 4 locks held by systemd-udevd/1538:
[ 17.717663] #0: (____ptrval____) (&dev->mutex){....}, at: __driver_attach+0x134/0x1e4
[ 17.725760] #1: (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: cpufreq_register_driver+0xd8/0x278
[ 17.735517] #2: (____ptrval____) (subsys mutex#6){+.+.}, at: subsys_interface_register+0x10c/0x264
[ 17.744761] #3: (____ptrval____) (opp_table_lock){+.+.}, at: dev_pm_opp_get_opp_table+0xac/0x310
[ 17.753811]
[ 17.753811] stack backtrace:
[ 17.758252] CPU: 4 PID: 1538 Comm: systemd-udevd Not tainted 4.18.0-rc6 #3
[ 17.765215] Hardware name: Renesas Salvator-X board based on r8a7795 ES2.0+ (DT)
[ 17.772708] Call trace:
[ 17.775209] dump_backtrace+0x0/0x27c
[ 17.778931] show_stack+0x24/0x30
[ 17.782313] dump_stack+0x13c/0x1b0
[ 17.785868] print_circular_bug.isra.12+0x2a8/0x3f8
[ 17.790826] check_prev_add.constprop.20+0x1a4/0xb24
[ 17.795869] __lock_acquire+0x1968/0x1f4c
[ 17.799948] lock_acquire+0x578/0x5c0
[ 17.803675] down_write+0xb8/0x148
[ 17.807143] start_creating+0xbc/0x140
[ 17.810962] debugfs_create_dir+0x2c/0x1b0
[ 17.815125] opp_debug_register+0xc4/0x10c
[ 17.819287] _add_opp_dev+0x178/0x1d8
[ 17.823012] dev_pm_opp_get_opp_table+0x134/0x310
[ 17.827789] dev_pm_opp_set_regulators+0x38/0x300
[ 17.832596] cpufreq_init+0x198/0x3e0 [cpufreq_dt]
[ 17.837464] cpufreq_online+0x3f0/0xcd4
[ 17.841366] cpufreq_add_dev+0x164/0x17c
[ 17.845360] subsys_interface_register+0x244/0x264
[ 17.850228] cpufreq_register_driver+0x178/0x278
[ 17.854943] dt_cpufreq_probe+0x158/0x178 [cpufreq_dt]
[ 17.860158] platform_drv_probe+0xa4/0x134
[ 17.864326] driver_probe_device+0x36c/0x488
[ 17.868670] __driver_attach+0x150/0x1e4
[ 17.872661] bus_for_each_dev+0x110/0x138
[ 17.876740] driver_attach+0x50/0x5c
[ 17.880381] bus_add_driver+0x2ac/0x2f8
[ 17.884287] driver_register+0x180/0x1c8
[ 17.888283] __platform_driver_register+0x9c/0xac
[ 17.893087] dt_cpufreq_platdrv_init+0x28/0x1000 [cpufreq_dt]
[ 17.898918] do_one_initcall+0x59c/0xab0
[ 17.902912] do_init_module+0x174/0x450
[ 17.906818] load_module+0x3a40/0x3b60
[ 17.910636] sys_finit_module+0x150/0x168
[ 17.914712] el0_svc_naked+0x30/0x34

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