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SubjectRe: [PATCH] cpufreq: governor: Protect cpufreq governor_data
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Date
Hi folks,

On 08/14/2018 08:01 PM, Henry Willard wrote:
> If cppc_cpufreq.ko is deleted at the same time that tuned-adm is,
> changing profiles, there is a small chance that a race can occur
> between cpufreq_dbs_governor_exit() and cpufreq_dbs_governor_limits()
> resulting in a system failure when the latter tries to use
> policy->governor_data that has been freed by the former.
>
> This patch uses gov_dbs_data_mutex to synchronize access.
>
> Signed-off-by: Henry Willard <henry.willard@oracle.com>
> ---
> drivers/cpufreq/cpufreq_governor.c | 10 +++++++++-
> 1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c
> index 1d50e97d49f1..43416ee55849 100644
> --- a/drivers/cpufreq/cpufreq_governor.c
> +++ b/drivers/cpufreq/cpufreq_governor.c
> @@ -555,12 +555,20 @@ void cpufreq_dbs_governor_stop(struct cpufreq_policy *policy)
>
> void cpufreq_dbs_governor_limits(struct cpufreq_policy *policy)
> {
> - struct policy_dbs_info *policy_dbs = policy->governor_data;
> + struct policy_dbs_info *policy_dbs;
> +
> + /* Protect gov->gdbs_data against cpufreq_dbs_governor_exit */
> + mutex_lock(&gov_dbs_data_mutex);
> + policy_dbs = policy->governor_data;
> + if (!policy_dbs)
> + goto out;
>
> mutex_lock(&policy_dbs->update_mutex);
> cpufreq_policy_apply_limits(policy);
> gov_update_sample_delay(policy_dbs, 0);
>
> mutex_unlock(&policy_dbs->update_mutex);
> +out:
> + mutex_unlock(&gov_dbs_data_mutex);
> }
> EXPORT_SYMBOL_GPL(cpufreq_dbs_governor_limits);
>

Fedora has gotten a report[0] of possible circular locking which looks
like might have been introduced by this patch.

[0] https://bugzilla.redhat.com/show_bug.cgi?id=1627950

User-provided log (attached to the bug report) is:

======================================================
WARNING: possible circular locking dependency detected
4.19.0-0.rc2.git3.1.fc30.x86_64 #1 Not tainted
------------------------------------------------------
kworker/0:3/101 is trying to acquire lock:
000000003b2babfd ((work_completion)(&wfc.work)){+.+.}, at:
__flush_work+0x28c/0x320

but task is already holding lock:
0000000084d461de (&policy_dbs->update_mutex){+.+.}, at:
dbs_work_handler+0x2b/0x70

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #5 (&policy_dbs->update_mutex){+.+.}:
cpufreq_dbs_governor_limits+0x31/0x80
cpufreq_start_governor+0x65/0xa0
cpufreq_set_policy+0x2b7/0x330
cpufreq_init_policy+0x76/0xe0
cpufreq_online+0x535/0x6b0
cpufreq_add_dev+0x6b/0x80
subsys_interface_register+0xf3/0x150
cpufreq_register_driver+0x11e/0x230
powernowk8_init+0x134/0x18f [powernow_k8]
do_one_initcall+0x5d/0x2be
do_init_module+0x5a/0x210
load_module+0x2134/0x2400
__do_sys_init_module+0x150/0x1a0
do_syscall_64+0x60/0x1f0
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #4 (gov_dbs_data_mutex){+.+.}:
cpufreq_dbs_governor_init+0x117/0x240
cpufreq_init_governor+0x62/0xe0
cpufreq_set_policy+0x1ca/0x330
cpufreq_init_policy+0x76/0xe0
cpufreq_online+0x535/0x6b0
cpufreq_add_dev+0x6b/0x80
subsys_interface_register+0xf3/0x150
cpufreq_register_driver+0x11e/0x230
powernowk8_init+0x134/0x18f [powernow_k8]
do_one_initcall+0x5d/0x2be
do_init_module+0x5a/0x210
load_module+0x2134/0x2400
__do_sys_init_module+0x150/0x1a0
do_syscall_64+0x60/0x1f0
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #3 (&policy->rwsem){+.+.}:
cpufreq_policy_free+0xba/0x140
cpufreq_online+0xec/0x6b0
cpufreq_add_dev+0x6b/0x80
subsys_interface_register+0xf3/0x150
cpufreq_register_driver+0x11e/0x230
0xffffffffc05fc25a
do_one_initcall+0x5d/0x2be
do_init_module+0x5a/0x210
load_module+0x2134/0x2400
__do_sys_init_module+0x150/0x1a0
do_syscall_64+0x60/0x1f0
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #2 (subsys mutex#7){+.+.}:
subsys_interface_register+0x73/0x150
cpufreq_register_driver+0x11e/0x230
0xffffffffc05fc25a
do_one_initcall+0x5d/0x2be
do_init_module+0x5a/0x210
load_module+0x2134/0x2400
__do_sys_init_module+0x150/0x1a0
do_syscall_64+0x60/0x1f0
entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (cpu_hotplug_lock.rw_sem){.+.+}:
apply_workqueue_attrs+0x12/0x50
__alloc_workqueue_key+0x303/0x480
scsi_host_alloc+0x3be/0x450
ata_scsi_add_hosts+0xc9/0x150
ata_host_register+0x120/0x1d0
ata_host_activate+0xc1/0x140
svia_init_one+0x6c7/0x7f6 [sata_via]
local_pci_probe+0x41/0x90
work_for_cpu_fn+0x16/0x20
process_one_work+0x27d/0x5c0
worker_thread+0x3c/0x390
kthread+0x120/0x140
ret_from_fork+0x3a/0x50

-> #0 ((work_completion)(&wfc.work)){+.+.}:
__flush_work+0x2ac/0x320
work_on_cpu+0x9b/0xd0
powernowk8_target+0x33/0x50 [powernow_k8]
__cpufreq_driver_target+0x2d2/0x580
od_dbs_update+0xbb/0x190
dbs_work_handler+0x3a/0x70
process_one_work+0x27d/0x5c0
worker_thread+0x3c/0x390
kthread+0x120/0x140
ret_from_fork+0x3a/0x50

other info that might help us debug this:
Chain exists of:
(work_completion)(&wfc.work) --> gov_dbs_data_mutex -->
&policy_dbs->update_mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&policy_dbs->update_mutex);
lock(gov_dbs_data_mutex);
lock(&policy_dbs->update_mutex);
lock((work_completion)(&wfc.work));

*** DEADLOCK ***
3 locks held by kworker/0:3/101:
#0: 000000009eaebf60 ((wq_completion)"events"){+.+.}, at:
process_one_work+0x1f3/0x5c0
#1: 00000000ac2fb241 ((work_completion)(&policy_dbs->work)){+.+.}, at:
process_one_work+0x1f3/0x5c0
#2: 0000000084d461de (&policy_dbs->update_mutex){+.+.}, at:
dbs_work_handler+0x2b/0x70

stack backtrace:
CPU: 0 PID: 101 Comm: kworker/0:3 Not tainted
4.19.0-0.rc2.git3.1.fc30.x86_64 #1
Hardware name: Acer Aspire T135/K8VM800MAE, BIOS R01-A3 06/27/2005
Workqueue: events dbs_work_handler
Call Trace:
dump_stack+0x85/0xc0
print_circular_bug.isra.36.cold.55+0x15c/0x195
__lock_acquire+0x139a/0x16c0
? __lock_acquire+0x112b/0x16c0
lock_acquire+0x9e/0x180
? __flush_work+0x28c/0x320
__flush_work+0x2ac/0x320
? __flush_work+0x28c/0x320
? native_sched_clock+0x3e/0xa0
? mark_held_locks+0x57/0x80
? queue_work_on+0x5d/0x90
? lockdep_hardirqs_on+0xed/0x180
work_on_cpu+0x9b/0xd0
? work_is_static_object+0x10/0x10
? write_new_fid+0xe0/0xe0 [powernow_k8]
powernowk8_target+0x33/0x50 [powernow_k8]
__cpufreq_driver_target+0x2d2/0x580
od_dbs_update+0xbb/0x190
dbs_work_handler+0x3a/0x70
process_one_work+0x27d/0x5c0
worker_thread+0x3c/0x390
? process_one_work+0x5c0/0x5c0
kthread+0x120/0x140
? kthread_create_worker_on_cpu+0x70/0x70
ret_from_fork+0x3a/0x50
clocksource: timekeeping watchdog on CPU0: Marking clocksource 'tsc' as
unstable because the skew is too large:
clocksource: 'acpi_pm' wd_now: 61cb7c wd_last:
5e7744 mask: ffffff
clocksource: 'tsc' cs_now: 2b9d83ad41 cs_last:
299dc3ef91 mask: ffffffffffffffff
tsc: Marking TSC unstable due to clocksource watchdog
TSC found unstable after boot, most likely due to broken BIOS. Use
'tsc=unstable'.
sched_clock: Marking unstable (55064379271, 12383389)<-(55179340298,
-102501740)
clocksource: Switched to clocksource acpi_pm


Cheers,
Jeremy

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