Hi,
Commit 2f7021a8 ("cpufreq: protect 'policy->cpus' from offlining during
__gov_queue_work()") causes the following deadlock for me when using kernel
v3.10 on ARM EXYNOS4412:
[ 960.380000] INFO: task kworker/0:1:34 blocked for more than 120 seconds.
[ 960.385000] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
[ 960.390000] kworker/0:1 D c0613d88 0 34 2 0x00000000
[ 960.395000] Workqueue: events od_dbs_timer
[ 960.400000] [<c0613d88>] (__schedule+0x39c/0x7ec) from [<c06145e8>]
(schedule_preempt_disabled+0x24/0x34)
[ 960.410000] [<c06145e8>] (schedule_preempt_disabled+0x24/0x34) from
[<c0612fe4>] (__mutex_lock_slowpath+0x15c/0x21c)
[ 960.420000] [<c0612fe4>] (__mutex_lock_slowpath+0x15c/0x21c) from
[<c06130ec>] (mutex_lock+0x48/0x4c)
[ 960.430000] [<c06130ec>] (mutex_lock+0x48/0x4c) from [<c0027cdc>]
(get_online_cpus+0x2c/0x48)
[ 960.440000] [<c0027cdc>] (get_online_cpus+0x2c/0x48) from [<c03b059c>]
(gov_queue_work+0x1c/0xb8)
[ 960.450000] [<c03b059c>] (gov_queue_work+0x1c/0xb8) from [<c03afabc>]
(od_dbs_timer+0xa8/0x12c)
[ 960.455000] [<c03afabc>] (od_dbs_timer+0xa8/0x12c) from [<c003ecdc>]
(process_one_work+0x138/0x43c)
[ 960.465000] [<c003ecdc>] (process_one_work+0x138/0x43c) from [<c003f3d8>]
(worker_thread+0x134/0x3b8)
[ 960.475000] [<c003f3d8>] (worker_thread+0x134/0x3b8) from [<c0044df8>]
(kthread+0xa4/0xb0)
[ 960.485000] [<c0044df8>] (kthread+0xa4/0xb0) from [<c000ead8>]
(ret_from_fork+0x14/0x3c)
[ 960.490000] INFO: task bash:2497 blocked for more than 120 seconds.
[ 960.495000] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this
message.
[ 960.505000] bash D c0613d88 0 2497 2496 0x00000001
[ 960.510000] [<c0613d88>] (__schedule+0x39c/0x7ec) from [<c061244c>]
(schedule_timeout+0x14c/0x20c)
[ 960.520000] [<c061244c>] (schedule_timeout+0x14c/0x20c) from [<c0613774>]
(wait_for_common+0xac/0x150)
[ 960.530000] [<c0613774>] (wait_for_common+0xac/0x150) from [<c003deb8>]
(flush_work+0xa4/0x130)
[ 960.540000] [<c003deb8>] (flush_work+0xa4/0x130) from [<c003f9d4>]
(__cancel_work_timer+0x74/0x100)
[ 960.545000] [<c003f9d4>] (__cancel_work_timer+0x74/0x100) from [<c03b0dc8>]
(cpufreq_governor_dbs+0x4dc/0x630)
[ 960.555000] [<c03b0dc8>] (cpufreq_governor_dbs+0x4dc/0x630) from
[<c03ac70c>] (__cpufreq_governor+0x60/0x120)
[ 960.565000] [<c03ac70c>] (__cpufreq_governor+0x60/0x120) from [<c03ad1cc>]
(cpufreq_add_dev+0x2f4/0x4d8)
[ 960.575000] [<c03ad1cc>] (cpufreq_add_dev+0x2f4/0x4d8) from [<c060dcd8>]
(cpufreq_cpu_callback+0x54/0x5c)
[ 960.585000] [<c060dcd8>] (cpufreq_cpu_callback+0x54/0x5c) from [<c004a280>]
(notifier_call_chain+0x44/0x84)
[ 960.595000] [<c004a280>] (notifier_call_chain+0x44/0x84) from [<c0027c94>]
(__cpu_notify+0x2c/0x48)
[ 960.605000] [<c0027c94>] (__cpu_notify+0x2c/0x48) from [<c060b914>]
(_cpu_up+0x10c/0x15c)
[ 960.615000] [<c060b914>] (_cpu_up+0x10c/0x15c) from [<c060b9c8>]
(cpu_up+0x64/0x80)
[ 960.620000] [<c060b9c8>] (cpu_up+0x64/0x80) from [<c060a704>]
(store_online+0x4c/0x74)
[ 960.630000] [<c060a704>] (store_online+0x4c/0x74) from [<c02b88b4>]
(dev_attr_store+0x18/0x24)
[ 960.635000] [<c02b88b4>] (dev_attr_store+0x18/0x24) from [<c014f43c>]
(sysfs_write_file+0xfc/0x164)
[ 960.645000] [<c014f43c>] (sysfs_write_file+0xfc/0x164) from [<c00f6e70>]
(vfs_write+0xbc/0x184)
[ 960.655000] [<c00f6e70>] (vfs_write+0xbc/0x184) from [<c00f7208>]
(SyS_write+0x40/0x68)
[ 960.665000] [<c00f7208>] (SyS_write+0x40/0x68) from [<c000ea40>]
(ret_fast_syscall+0x0/0x30)
Tomek has also managed to got a lockdep info for the problem:
[ 36.570161]
[ 36.570233] ======================================================
[ 36.576376] [ INFO: possible circular locking dependency detected ]
[ 36.582637] 3.10.0-rc5-00336-g6905065-dirty #1069 Not tainted
[ 36.588355] -------------------------------------------------------
[ 36.594608] bash/2783 is trying to acquire lock:
[ 36.599205] ((&(&j_cdbs->work)->work)){+.+.+.}, at: [<c0042138>]
flush_work+0x0/0x27c
[ 36.607104]
[ 36.607104] but task is already holding lock:
[ 36.612917] (cpu_hotplug.lock){+.+.+.}, at: [<c0028cb0>]
cpu_hotplug_begin+0x2c/0x58
[ 36.620731]
[ 36.620731] which lock already depends on the new lock.
[ 36.620731]
[ 36.628890]
[ 36.628890] the existing dependency chain (in reverse order) is:
[ 36.636355]
-> #2 (cpu_hotplug.lock){+.+.+.}:
[ 36.640867] [<c007c828>] lock_acquire+0x9c/0x130
[ 36.646075] [<c0643dc4>] mutex_lock_nested+0x68/0x3ec
[ 36.651716] [<c0028db0>] get_online_cpus+0x40/0x60
[ 36.657097] [<c03c2810>] gov_queue_work+0x1c/0xac
[ 36.662392] [<c03c18c4>] od_dbs_timer+0xb8/0x16c
[ 36.667600] [<c00415f8>] process_one_work+0x198/0x4d8
[ 36.673242] [<c0042998>] worker_thread+0x134/0x3e8
[ 36.678624] [<c0048ad8>] kthread+0xa8/0xb4
[ 36.683311] [<c000ee88>] ret_from_fork+0x14/0x2c
[ 36.688522]
-> #1 (&j_cdbs->timer_mutex){+.+.+.}:
[ 36.693380] [<c007c828>] lock_acquire+0x9c/0x130
[ 36.698588] [<c0643dc4>] mutex_lock_nested+0x68/0x3ec
[ 36.704229] [<c03c184c>] od_dbs_timer+0x40/0x16c
[ 36.709438] [<c00415f8>] process_one_work+0x198/0x4d8
[ 36.715080] [<c0042998>] worker_thread+0x134/0x3e8
[ 36.720461] [<c0048ad8>] kthread+0xa8/0xb4
[ 36.725148] [<c000ee88>] ret_from_fork+0x14/0x2c
[ 36.730360]
-> #0 ((&(&j_cdbs->work)->work)){+.+.+.}:
[ 36.735565] [<c007bb70>] __lock_acquire+0x17c0/0x1e64
[ 36.741206] [<c007c828>] lock_acquire+0x9c/0x130
[ 36.746414] [<c0042170>] flush_work+0x38/0x27c
[ 36.751449] [<c00424e8>] __cancel_work_timer+0x84/0x120
[ 36.757265] [<c03c3040>] cpufreq_governor_dbs+0x4f4/0x674
[ 36.763254] [<c03bdeac>] __cpufreq_governor+0x60/0x120
[ 36.768983] [<c03bfaa0>] __cpufreq_remove_dev.clone.4+0x7c/0x480
[ 36.775579] [<c06421d0>] cpufreq_cpu_callback+0x48/0x5c
[ 36.781396] [<c004e688>] notifier_call_chain+0x44/0x84
[ 36.787124] [<c0028c30>] __cpu_notify+0x2c/0x48
[ 36.792245] [<c063de9c>] _cpu_down+0xb4/0x238
[ 36.797193] [<c063e048>] cpu_down+0x28/0x3c
[ 36.801966] [<c063e9c0>] store_online+0x30/0x74
[ 36.807088] [<c02c9bbc>] dev_attr_store+0x18/0x24
[ 36.812382] [<c0166e08>] sysfs_write_file+0x104/0x18c
[ 36.818025] [<c010b704>] vfs_write+0xc8/0x194
[ 36.822973] [<c010bac0>] SyS_write+0x44/0x70
[ 36.827833] [<c000edc0>] ret_fast_syscall+0x0/0x48
[ 36.833218]
[ 36.833218] other info that might help us debug this:
[ 36.833218]
[ 36.841203] Chain exists of:
(&(&j_cdbs->work)->work) --> &j_cdbs->timer_mutex --> cpu_hotplug.lock
[ 36.850663] Possible unsafe locking scenario:
[ 36.850663]
[ 36.856565] CPU0 CPU1
[ 36.861079] ---- ----
[ 36.865591] lock(cpu_hotplug.lock);
[ 36.869237] lock(&j_cdbs->timer_mutex);
[ 36.875746] lock(cpu_hotplug.lock);
[ 36.881909] lock((&(&j_cdbs->work)->work));
[ 36.886250]
[ 36.886250] *** DEADLOCK ***
[ 36.886250]
[ 36.892163] 5 locks held by bash/2783:
[ 36.895886] #0: (sb_writers#7){.+.+.+}, at: [<c010b7cc>]
vfs_write+0x190/0x194
[ 36.903264] #1: (&buffer->mutex){+.+.+.}, at: [<c0166d2c>]
sysfs_write_file+0x28/0x18c
[ 36.911336] #2: (s_active#50){.+.+..}, at: [<c0166de4>]
sysfs_write_file+0xe0/0x18c
[ 36.919148] #3: (cpu_add_remove_lock){+.+.+.}, at: [<c063e02c>]
cpu_down+0xc/0x3c
[ 36.926787] #4: (cpu_hotplug.lock){+.+.+.}, at: [<c0028cb0>]
cpu_hotplug_begin+0x2c/0x58
[ 36.935032]
[ 36.935032] stack backtrace:
[ 36.939394] CPU: 1 PID: 2783 Comm: bash Not tainted
3.10.0-rc5-00336-g6905065-dirty #1069
[ 36.947591] [<c0015ed0>] (unwind_backtrace+0x0/0x13c) from [<c0012e58>]
(show_stack+0x10/0x14)
[ 36.956164] [<c0012e58>] (show_stack+0x10/0x14) from [<c0078a9c>]
(print_circular_bug+0x1c8/0x304)
[ 36.965105] [<c0078a9c>] (print_circular_bug+0x1c8/0x304) from [<c007bb70>]
(__lock_acquire+0x17c0/0x1e64)
[ 36.974735] [<c007bb70>] (__lock_acquire+0x17c0/0x1e64) from [<c007c828>]
(lock_acquire+0x9c/0x130)
[ 36.983767] [<c007c828>] (lock_acquire+0x9c/0x130) from [<c0042170>]
(flush_work+0x38/0x27c)
[ 36.992187] [<c0042170>] (flush_work+0x38/0x27c) from [<c00424e8>]
(__cancel_work_timer+0x84/0x120)
[ 37.001225] [<c00424e8>] (__cancel_work_timer+0x84/0x120) from [<c03c3040>]
(cpufreq_governor_dbs+0x4f4/0x674)
[ 37.011196] [<c03c3040>] (cpufreq_governor_dbs+0x4f4/0x674) from
[<c03bdeac>] (__cpufreq_governor+0x60/0x120)
[ 37.021087] [<c03bdeac>] (__cpufreq_governor+0x60/0x120) from [<c03bfaa0>]
(__cpufreq_remove_dev.clone.4+0x7c/0x480)
[ 37.031607] [<c03bfaa0>] (__cpufreq_remove_dev.clone.4+0x7c/0x480) from
[<c06421d0>] (cpufreq_cpu_callback+0x48/0x5c)
[ 37.042207] [<c06421d0>] (cpufreq_cpu_callback+0x48/0x5c) from [<c004e688>]
(notifier_call_chain+0x44/0x84)
[ 37.051910] [<c004e688>] (notifier_call_chain+0x44/0x84) from [<c0028c30>]
(__cpu_notify+0x2c/0x48)
[ 37.060931] [<c0028c30>] (__cpu_notify+0x2c/0x48) from [<c063de9c>]
(_cpu_down+0xb4/0x238)
[ 37.069177] [<c063de9c>] (_cpu_down+0xb4/0x238) from [<c063e048>]
(cpu_down+0x28/0x3c)
[ 37.077074] [<c063e048>] (cpu_down+0x28/0x3c) from [<c063e9c0>]
(store_online+0x30/0x74)
[ 37.085147] [<c063e9c0>] (store_online+0x30/0x74) from [<c02c9bbc>]
(dev_attr_store+0x18/0x24)
[ 37.093740] [<c02c9bbc>] (dev_attr_store+0x18/0x24) from [<c0166e08>]
(sysfs_write_file+0x104/0x18c)
[ 37.102852] [<c0166e08>] (sysfs_write_file+0x104/0x18c) from [<c010b704>]
(vfs_write+0xc8/0x194)
[ 37.111616] [<c010b704>] (vfs_write+0xc8/0x194) from [<c010bac0>]
(SyS_write+0x44/0x70)
[ 37.119613] [<c010bac0>] (SyS_write+0x44/0x70) from [<c000edc0>]
(ret_fast_syscall+0x0/0x48)
Reproducing the issue is very easy, i.e.:
# echo 0 > /sys/devices/system/cpu/cpu3/online
# echo 0 > /sys/devices/system/cpu/cpu2/online
# echo 0 > /sys/devices/system/cpu/cpu1/online
# while true;do echo 1 > /sys/devices/system/cpu/cpu1/online;echo 0 >
/sys/devices/system/cpu/cpu1/online;done
The commit in question (2f7021a8) was merged in v3.10-rc5 as a fix for
commit 031299b ("cpufreq: governors: Avoid unnecessary per cpu timer
interrupts") which was causing a kernel warning to show up.
Michael/Viresh: do you have some idea how to fix the issue?
Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics
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