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* [PATCH] cpufreq: fix another race between PPC notification and vcpu_hotplug()
@ 2015-01-29  6:42 Ethan Zhao
  2015-01-29  8:38 ` Viresh Kumar
  0 siblings, 1 reply; 5+ messages in thread
From: Ethan Zhao @ 2015-01-29  6:42 UTC (permalink / raw)
  To: rjw, viresh.kumar; +Cc: linux-pm, linux-kernel, ethan.kernel, Ethan Zhao

There is race observed between PPC changed notification handler worker thread
and vcpu_hotplug() called within xenbus_thread() context.
It is shown as following WARNING:

 ------------[ cut here ]------------
 WARNING: CPU: 0 PID: 4 at include/linux/kref.h:47
 kobject_get+0x41/0x50()
 Modules linked in: acpi_cpufreq(+) nfsd auth_rpcgss nfs_acl
 lockd grace sunrpc xfs libcrc32c sd_mod ixgbe igb mdio ahci hwmon
 ...
 [   14.003548] CPU: 0 PID: 4 Comm: kworker/0:0 Not tainted
 ...
 [   14.003553] Workqueue: kacpi_notify acpi_os_execute_deferred
 [   14.003554]  0000000000000000 000000008c76682c ffff88094c793af8
 ffffffff81661b14
 [   14.003556]  0000000000000000 0000000000000000 ffff88094c793b38
 ffffffff81072b61
 [   14.003558]  ffff88094c793bd8 ffff8812491f8800 0000000000000292
 0000000000000000
 [   14.003560] Call Trace:
 [   14.003567]  [<ffffffff81661b14>] dump_stack+0x46/0x58
 [   14.003571]  [<ffffffff81072b61>] warn_slowpath_common+0x81/0xa0
 [   14.003572]  [<ffffffff81072c7a>] warn_slowpath_null+0x1a/0x20
 [   14.003574]  [<ffffffff812e16d1>] kobject_get+0x41/0x50
 [   14.003579]  [<ffffffff815262a5>] cpufreq_cpu_get+0x75/0xc0
 [   14.003581]  [<ffffffff81527c3e>] cpufreq_update_policy+0x2e/0x1f0
 [   14.003586]  [<ffffffff810b8cb2>] ? up+0x32/0x50
 [   14.003589]  [<ffffffff81381aa9>] ? acpi_ns_get_node+0xcb/0xf2
 [   14.003591]  [<ffffffff81381efd>] ? acpi_evaluate_object+0x22c/0x252
 [   14.003593]  [<ffffffff813824f6>] ? acpi_get_handle+0x95/0xc0
 [   14.003596]  [<ffffffff81360967>] ? acpi_has_method+0x25/0x40
 [   14.003601]  [<ffffffff81391e08>] acpi_processor_ppc_has_changed+0x77/0x82
 [   14.003604]  [<ffffffff81089566>] ? move_linked_works+0x66/0x90
 [   14.003606]  [<ffffffff8138e8ed>] acpi_processor_notify+0x58/0xe7
 [   14.003609]  [<ffffffff8137410c>] acpi_ev_notify_dispatch+0x44/0x5c
 [   14.003611]  [<ffffffff8135f293>] acpi_os_execute_deferred+0x15/0x22
 [   14.003614]  [<ffffffff8108c910>] process_one_work+0x160/0x410
 [   14.003616]  [<ffffffff8108d05b>] worker_thread+0x11b/0x520
 [   14.003617]  [<ffffffff8108cf40>] ? rescuer_thread+0x380/0x380
 [   14.003621]  [<ffffffff81092421>] kthread+0xe1/0x100
 [   14.003623]  [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0
 [   14.003628]  [<ffffffff81669ebc>] ret_from_fork+0x7c/0xb0
 [   14.003630]  [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0
 [   14.003631] ---[ end trace 89e66eb9795efdf7 ]---

 Thread A: Workqueue: kacpi_notify

 acpi_processor_notify()
   acpi_processor_ppc_has_changed()
	 cpufreq_update_policy()
	   cpufreq_cpu_get()
             kobject_get()

 Thread B: xenbus_thread()

 xenbus_thread()
   msg->u.watch.handle->callback()
     handle_vcpu_hotplug_event()
       vcpu_hotplug()
         cpu_down()
           __cpu_notify(CPU_DOWN_PREPARE..)
             cpufreq_cpu_callback()
               __cpufreq_remove_dev_prepare()
                 update_policy_cpu()
                   kobject_move()

To avoid this race, cpufreq_cpu_get() should check the cpu is offline or not
and move the kobject_move() after up_write(&policy->rwsem) in function
update_policy_cpu() to be sure the updating to the policy was done in another
thread. 

But seems it is not complete fix because of some functions would schedule out
we could couldn't move them into sections proteced by rwsem directly, such as
the move_object().

Only passed buidling with v3.19-rc6.

Signed-off-by: Ethan Zhao <ethan.zhao@oracle.com>
---
 drivers/cpufreq/cpufreq.c | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 46bed4f..b5e2bb8 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -202,7 +202,7 @@ struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
 	struct cpufreq_policy *policy = NULL;
 	unsigned long flags;
 
-	if (cpufreq_disabled() || (cpu >= nr_cpu_ids))
+	if (cpufreq_disabled() || cpu_is_offline(cpu))
 		return NULL;
 
 	if (!down_read_trylock(&cpufreq_rwsem))
@@ -214,10 +214,18 @@ struct cpufreq_policy *cpufreq_cpu_get(unsigned int cpu)
 	if (cpufreq_driver) {
 		/* get the CPU */
 		policy = per_cpu(cpufreq_cpu_data, cpu);
-		if (policy)
-			kobject_get(&policy->kobj);
+		if (!policy)
+			goto out;
+
+		if (policy->cpu != cpu) {
+			policy = NULL;
+			goto out;
+		}
+
+		kobject_get(&policy->kobj);
 	}
 
+out:
 	read_unlock_irqrestore(&cpufreq_driver_lock, flags);
 
 	if (!policy)
@@ -1083,13 +1091,6 @@ static int update_policy_cpu(struct cpufreq_policy *policy, unsigned int cpu,
 	if (WARN_ON(cpu == policy->cpu))
 		return 0;
 
-	/* Move kobject to the new policy->cpu */
-	ret = kobject_move(&policy->kobj, &cpu_dev->kobj);
-	if (ret) {
-		pr_err("%s: Failed to move kobj: %d\n", __func__, ret);
-		return ret;
-	}
-
 	down_write(&policy->rwsem);
 
 	policy->last_cpu = policy->cpu;
@@ -1097,6 +1098,13 @@ static int update_policy_cpu(struct cpufreq_policy *policy, unsigned int cpu,
 
 	up_write(&policy->rwsem);
 
+	/* Move kobject to the new policy->cpu */
+	ret = kobject_move(&policy->kobj, &cpu_dev->kobj);
+	if (ret) {
+		pr_err("%s: Failed to move kobj: %d\n", __func__, ret);
+		return ret;
+	}
+
 	blocking_notifier_call_chain(&cpufreq_policy_notifier_list,
 			CPUFREQ_UPDATE_POLICY_CPU, policy);
 
-- 
1.8.3.1


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] cpufreq: fix another race between PPC notification and vcpu_hotplug()
  2015-01-29  6:42 [PATCH] cpufreq: fix another race between PPC notification and vcpu_hotplug() Ethan Zhao
@ 2015-01-29  8:38 ` Viresh Kumar
  2015-01-29 21:14   ` santosh shilimkar
  2015-01-30  1:44   ` ethan zhao
  0 siblings, 2 replies; 5+ messages in thread
From: Viresh Kumar @ 2015-01-29  8:38 UTC (permalink / raw)
  To: Ethan Zhao, santosh shilimkar
  Cc: Rafael J. Wysocki, linux-pm, Linux Kernel Mailing List, Ethan Zhao

Looks like you just save my time here, Santosh has also reported a
similar race in a personal mail..

On 29 January 2015 at 12:12, Ethan Zhao <ethan.zhao@oracle.com> wrote:
> There is race observed between PPC changed notification handler worker thread
> and vcpu_hotplug() called within xenbus_thread() context.
> It is shown as following WARNING:
>
>  ------------[ cut here ]------------
>  WARNING: CPU: 0 PID: 4 at include/linux/kref.h:47
>  kobject_get+0x41/0x50()
>  Modules linked in: acpi_cpufreq(+) nfsd auth_rpcgss nfs_acl
>  lockd grace sunrpc xfs libcrc32c sd_mod ixgbe igb mdio ahci hwmon
>  ...
>  [   14.003548] CPU: 0 PID: 4 Comm: kworker/0:0 Not tainted
>  ...
>  [   14.003553] Workqueue: kacpi_notify acpi_os_execute_deferred
>  [   14.003554]  0000000000000000 000000008c76682c ffff88094c793af8
>  ffffffff81661b14
>  [   14.003556]  0000000000000000 0000000000000000 ffff88094c793b38
>  ffffffff81072b61
>  [   14.003558]  ffff88094c793bd8 ffff8812491f8800 0000000000000292
>  0000000000000000
>  [   14.003560] Call Trace:
>  [   14.003567]  [<ffffffff81661b14>] dump_stack+0x46/0x58
>  [   14.003571]  [<ffffffff81072b61>] warn_slowpath_common+0x81/0xa0
>  [   14.003572]  [<ffffffff81072c7a>] warn_slowpath_null+0x1a/0x20
>  [   14.003574]  [<ffffffff812e16d1>] kobject_get+0x41/0x50
>  [   14.003579]  [<ffffffff815262a5>] cpufreq_cpu_get+0x75/0xc0
>  [   14.003581]  [<ffffffff81527c3e>] cpufreq_update_policy+0x2e/0x1f0
>  [   14.003586]  [<ffffffff810b8cb2>] ? up+0x32/0x50
>  [   14.003589]  [<ffffffff81381aa9>] ? acpi_ns_get_node+0xcb/0xf2
>  [   14.003591]  [<ffffffff81381efd>] ? acpi_evaluate_object+0x22c/0x252
>  [   14.003593]  [<ffffffff813824f6>] ? acpi_get_handle+0x95/0xc0
>  [   14.003596]  [<ffffffff81360967>] ? acpi_has_method+0x25/0x40
>  [   14.003601]  [<ffffffff81391e08>] acpi_processor_ppc_has_changed+0x77/0x82
>  [   14.003604]  [<ffffffff81089566>] ? move_linked_works+0x66/0x90
>  [   14.003606]  [<ffffffff8138e8ed>] acpi_processor_notify+0x58/0xe7
>  [   14.003609]  [<ffffffff8137410c>] acpi_ev_notify_dispatch+0x44/0x5c
>  [   14.003611]  [<ffffffff8135f293>] acpi_os_execute_deferred+0x15/0x22
>  [   14.003614]  [<ffffffff8108c910>] process_one_work+0x160/0x410
>  [   14.003616]  [<ffffffff8108d05b>] worker_thread+0x11b/0x520
>  [   14.003617]  [<ffffffff8108cf40>] ? rescuer_thread+0x380/0x380
>  [   14.003621]  [<ffffffff81092421>] kthread+0xe1/0x100
>  [   14.003623]  [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0
>  [   14.003628]  [<ffffffff81669ebc>] ret_from_fork+0x7c/0xb0
>  [   14.003630]  [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0
>  [   14.003631] ---[ end trace 89e66eb9795efdf7 ]---
>
>  Thread A: Workqueue: kacpi_notify
>
>  acpi_processor_notify()
>    acpi_processor_ppc_has_changed()
>          cpufreq_update_policy()
>            cpufreq_cpu_get()
>              kobject_get()
>
>  Thread B: xenbus_thread()
>
>  xenbus_thread()
>    msg->u.watch.handle->callback()
>      handle_vcpu_hotplug_event()
>        vcpu_hotplug()
>          cpu_down()
>            __cpu_notify(CPU_DOWN_PREPARE..)
>              cpufreq_cpu_callback()
>                __cpufreq_remove_dev_prepare()
>                  update_policy_cpu()
>                    kobject_move()

Where is the race ? How do you say this is racy ?

I am not sure if the problem is with kobject_move(), to me it looked like
the problem is with cpufreq_policy_put_kobj() and we tried to do kobject_get()
after the kobject has been freed..

I don't agree to the solution you gave, but lets first make sure what the
problem is, and then take any action against it.

Please try this patch and let us know if it fixes it for you:

diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
index 4473eba1d6b0..5ced9cca4822 100644
--- a/drivers/cpufreq/cpufreq.c
+++ b/drivers/cpufreq/cpufreq.c
@@ -1411,6 +1411,7 @@ static int __cpufreq_remove_dev_finish(struct device *dev,

        read_lock_irqsave(&cpufreq_driver_lock, flags);
        policy = per_cpu(cpufreq_cpu_data, cpu);
+       per_cpu(cpufreq_cpu_data, cpu) = NULL;
        read_unlock_irqrestore(&cpufreq_driver_lock, flags);

        if (!policy) {
@@ -1466,7 +1467,6 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
                }
        }

-       per_cpu(cpufreq_cpu_data, cpu) = NULL;
        return 0;
 }

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] cpufreq: fix another race between PPC notification and vcpu_hotplug()
  2015-01-29  8:38 ` Viresh Kumar
@ 2015-01-29 21:14   ` santosh shilimkar
  2015-01-30  1:44   ` ethan zhao
  1 sibling, 0 replies; 5+ messages in thread
From: santosh shilimkar @ 2015-01-29 21:14 UTC (permalink / raw)
  To: Viresh Kumar, Ethan Zhao
  Cc: Rafael J. Wysocki, linux-pm, Linux Kernel Mailing List, Ethan Zhao

On 1/29/2015 12:38 AM, Viresh Kumar wrote:
> Looks like you just save my time here, Santosh has also reported a
> similar race in a personal mail..
>
> On 29 January 2015 at 12:12, Ethan Zhao <ethan.zhao@oracle.com> wrote:
>> There is race observed between PPC changed notification handler worker thread
>> and vcpu_hotplug() called within xenbus_thread() context.
>> It is shown as following WARNING:
>>
>>   ------------[ cut here ]------------
>>   WARNING: CPU: 0 PID: 4 at include/linux/kref.h:47
>>   kobject_get+0x41/0x50()
>>   Modules linked in: acpi_cpufreq(+) nfsd auth_rpcgss nfs_acl
>>   lockd grace sunrpc xfs libcrc32c sd_mod ixgbe igb mdio ahci hwmon
>>   ...
>>   [   14.003548] CPU: 0 PID: 4 Comm: kworker/0:0 Not tainted
>>   ...
>>   [   14.003553] Workqueue: kacpi_notify acpi_os_execute_deferred
>>   [   14.003554]  0000000000000000 000000008c76682c ffff88094c793af8
>>   ffffffff81661b14
>>   [   14.003556]  0000000000000000 0000000000000000 ffff88094c793b38
>>   ffffffff81072b61
>>   [   14.003558]  ffff88094c793bd8 ffff8812491f8800 0000000000000292
>>   0000000000000000
>>   [   14.003560] Call Trace:
>>   [   14.003567]  [<ffffffff81661b14>] dump_stack+0x46/0x58
>>   [   14.003571]  [<ffffffff81072b61>] warn_slowpath_common+0x81/0xa0
>>   [   14.003572]  [<ffffffff81072c7a>] warn_slowpath_null+0x1a/0x20
>>   [   14.003574]  [<ffffffff812e16d1>] kobject_get+0x41/0x50
>>   [   14.003579]  [<ffffffff815262a5>] cpufreq_cpu_get+0x75/0xc0
>>   [   14.003581]  [<ffffffff81527c3e>] cpufreq_update_policy+0x2e/0x1f0
>>   [   14.003586]  [<ffffffff810b8cb2>] ? up+0x32/0x50
>>   [   14.003589]  [<ffffffff81381aa9>] ? acpi_ns_get_node+0xcb/0xf2
>>   [   14.003591]  [<ffffffff81381efd>] ? acpi_evaluate_object+0x22c/0x252
>>   [   14.003593]  [<ffffffff813824f6>] ? acpi_get_handle+0x95/0xc0
>>   [   14.003596]  [<ffffffff81360967>] ? acpi_has_method+0x25/0x40
>>   [   14.003601]  [<ffffffff81391e08>] acpi_processor_ppc_has_changed+0x77/0x82
>>   [   14.003604]  [<ffffffff81089566>] ? move_linked_works+0x66/0x90
>>   [   14.003606]  [<ffffffff8138e8ed>] acpi_processor_notify+0x58/0xe7
>>   [   14.003609]  [<ffffffff8137410c>] acpi_ev_notify_dispatch+0x44/0x5c
>>   [   14.003611]  [<ffffffff8135f293>] acpi_os_execute_deferred+0x15/0x22
>>   [   14.003614]  [<ffffffff8108c910>] process_one_work+0x160/0x410
>>   [   14.003616]  [<ffffffff8108d05b>] worker_thread+0x11b/0x520
>>   [   14.003617]  [<ffffffff8108cf40>] ? rescuer_thread+0x380/0x380
>>   [   14.003621]  [<ffffffff81092421>] kthread+0xe1/0x100
>>   [   14.003623]  [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0
>>   [   14.003628]  [<ffffffff81669ebc>] ret_from_fork+0x7c/0xb0
>>   [   14.003630]  [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0
>>   [   14.003631] ---[ end trace 89e66eb9795efdf7 ]---
>>
>>   Thread A: Workqueue: kacpi_notify
>>
>>   acpi_processor_notify()
>>     acpi_processor_ppc_has_changed()
>>           cpufreq_update_policy()
>>             cpufreq_cpu_get()
>>               kobject_get()
>>
>>   Thread B: xenbus_thread()
>>
>>   xenbus_thread()
>>     msg->u.watch.handle->callback()
>>       handle_vcpu_hotplug_event()
>>         vcpu_hotplug()
>>           cpu_down()
>>             __cpu_notify(CPU_DOWN_PREPARE..)
>>               cpufreq_cpu_callback()
>>                 __cpufreq_remove_dev_prepare()
>>                   update_policy_cpu()
>>                     kobject_move()
>
> Where is the race ? How do you say this is racy ?
>
> I am not sure if the problem is with kobject_move(), to me it looked like
> the problem is with cpufreq_policy_put_kobj() and we tried to do kobject_get()
> after the kobject has been freed..
>
> I don't agree to the solution you gave, but lets first make sure what the
> problem is, and then take any action against it.
>
> Please try this patch and let us know if it fixes it for you:
>
Yes it does fix the issue. Thanks Viresh

Regards,
Santosh

^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] cpufreq: fix another race between PPC notification and vcpu_hotplug()
  2015-01-29  8:38 ` Viresh Kumar
  2015-01-29 21:14   ` santosh shilimkar
@ 2015-01-30  1:44   ` ethan zhao
  2015-01-30  2:00     ` Viresh Kumar
  1 sibling, 1 reply; 5+ messages in thread
From: ethan zhao @ 2015-01-30  1:44 UTC (permalink / raw)
  To: Viresh Kumar
  Cc: santosh shilimkar, Rafael J. Wysocki, linux-pm,
	Linux Kernel Mailing List, Ethan Zhao

Viresh,

On 2015/1/29 16:38, Viresh Kumar wrote:
> Looks like you just save my time here, Santosh has also reported a
> similar race in a personal mail..
  As you know, Santosh is in the same cage as me.
>
> On 29 January 2015 at 12:12, Ethan Zhao <ethan.zhao@oracle.com> wrote:
>> There is race observed between PPC changed notification handler worker thread
>> and vcpu_hotplug() called within xenbus_thread() context.
>> It is shown as following WARNING:
>>
>>   ------------[ cut here ]------------
>>   WARNING: CPU: 0 PID: 4 at include/linux/kref.h:47
>>   kobject_get+0x41/0x50()
>>   Modules linked in: acpi_cpufreq(+) nfsd auth_rpcgss nfs_acl
>>   lockd grace sunrpc xfs libcrc32c sd_mod ixgbe igb mdio ahci hwmon
>>   ...
>>   [   14.003548] CPU: 0 PID: 4 Comm: kworker/0:0 Not tainted
>>   ...
>>   [   14.003553] Workqueue: kacpi_notify acpi_os_execute_deferred
>>   [   14.003554]  0000000000000000 000000008c76682c ffff88094c793af8
>>   ffffffff81661b14
>>   [   14.003556]  0000000000000000 0000000000000000 ffff88094c793b38
>>   ffffffff81072b61
>>   [   14.003558]  ffff88094c793bd8 ffff8812491f8800 0000000000000292
>>   0000000000000000
>>   [   14.003560] Call Trace:
>>   [   14.003567]  [<ffffffff81661b14>] dump_stack+0x46/0x58
>>   [   14.003571]  [<ffffffff81072b61>] warn_slowpath_common+0x81/0xa0
>>   [   14.003572]  [<ffffffff81072c7a>] warn_slowpath_null+0x1a/0x20
>>   [   14.003574]  [<ffffffff812e16d1>] kobject_get+0x41/0x50
>>   [   14.003579]  [<ffffffff815262a5>] cpufreq_cpu_get+0x75/0xc0
>>   [   14.003581]  [<ffffffff81527c3e>] cpufreq_update_policy+0x2e/0x1f0
>>   [   14.003586]  [<ffffffff810b8cb2>] ? up+0x32/0x50
>>   [   14.003589]  [<ffffffff81381aa9>] ? acpi_ns_get_node+0xcb/0xf2
>>   [   14.003591]  [<ffffffff81381efd>] ? acpi_evaluate_object+0x22c/0x252
>>   [   14.003593]  [<ffffffff813824f6>] ? acpi_get_handle+0x95/0xc0
>>   [   14.003596]  [<ffffffff81360967>] ? acpi_has_method+0x25/0x40
>>   [   14.003601]  [<ffffffff81391e08>] acpi_processor_ppc_has_changed+0x77/0x82
>>   [   14.003604]  [<ffffffff81089566>] ? move_linked_works+0x66/0x90
>>   [   14.003606]  [<ffffffff8138e8ed>] acpi_processor_notify+0x58/0xe7
>>   [   14.003609]  [<ffffffff8137410c>] acpi_ev_notify_dispatch+0x44/0x5c
>>   [   14.003611]  [<ffffffff8135f293>] acpi_os_execute_deferred+0x15/0x22
>>   [   14.003614]  [<ffffffff8108c910>] process_one_work+0x160/0x410
>>   [   14.003616]  [<ffffffff8108d05b>] worker_thread+0x11b/0x520
>>   [   14.003617]  [<ffffffff8108cf40>] ? rescuer_thread+0x380/0x380
>>   [   14.003621]  [<ffffffff81092421>] kthread+0xe1/0x100
>>   [   14.003623]  [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0
>>   [   14.003628]  [<ffffffff81669ebc>] ret_from_fork+0x7c/0xb0
>>   [   14.003630]  [<ffffffff81092340>] ? kthread_create_on_node+0x1b0/0x1b0
>>   [   14.003631] ---[ end trace 89e66eb9795efdf7 ]---
>>
>>   Thread A: Workqueue: kacpi_notify
>>
>>   acpi_processor_notify()
>>     acpi_processor_ppc_has_changed()
>>           cpufreq_update_policy()
>>             cpufreq_cpu_get()
>>               kobject_get()
>>
>>   Thread B: xenbus_thread()
>>
>>   xenbus_thread()
>>     msg->u.watch.handle->callback()
>>       handle_vcpu_hotplug_event()
>>         vcpu_hotplug()
>>           cpu_down()
>>             __cpu_notify(CPU_DOWN_PREPARE..)
>>               cpufreq_cpu_callback()
>>                 __cpufreq_remove_dev_prepare()
>>                   update_policy_cpu()
>>                     kobject_move()
> Where is the race ? How do you say this is racy ?
You see it. the policy had been moved to another CPU, you want the Thread A
continue to get the policy and update it ?
>
> I am not sure if the problem is with kobject_move(), to me it looked like
> the problem is with cpufreq_policy_put_kobj() and we tried to do kobject_get()
> after the kobject has been freed..
>
> I don't agree to the solution you gave, but lets first make sure what the
> problem is, and then take any action against it.
  Please take a look at the code I composed, I thought of it whole night.

  Thanks,
  Ethan
>
> Please try this patch and let us know if it fixes it for you:
>
> diff --git a/drivers/cpufreq/cpufreq.c b/drivers/cpufreq/cpufreq.c
> index 4473eba1d6b0..5ced9cca4822 100644
> --- a/drivers/cpufreq/cpufreq.c
> +++ b/drivers/cpufreq/cpufreq.c
> @@ -1411,6 +1411,7 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
>
>          read_lock_irqsave(&cpufreq_driver_lock, flags);
>          policy = per_cpu(cpufreq_cpu_data, cpu);
> +       per_cpu(cpufreq_cpu_data, cpu) = NULL;
>          read_unlock_irqrestore(&cpufreq_driver_lock, flags);
>
>          if (!policy) {
> @@ -1466,7 +1467,6 @@ static int __cpufreq_remove_dev_finish(struct device *dev,
>                  }
>          }
>
> -       per_cpu(cpufreq_cpu_data, cpu) = NULL;
>          return 0;
>   }


^ permalink raw reply	[flat|nested] 5+ messages in thread

* Re: [PATCH] cpufreq: fix another race between PPC notification and vcpu_hotplug()
  2015-01-30  1:44   ` ethan zhao
@ 2015-01-30  2:00     ` Viresh Kumar
  0 siblings, 0 replies; 5+ messages in thread
From: Viresh Kumar @ 2015-01-30  2:00 UTC (permalink / raw)
  To: ethan zhao
  Cc: santosh shilimkar, Rafael J. Wysocki, linux-pm,
	Linux Kernel Mailing List, Ethan Zhao

On 30 January 2015 at 07:14, ethan zhao <ethan.zhao@oracle.com> wrote:
>  Please take a look at the code I composed, I thought of it whole night.

Santosh has already tested my patch and it worked for him. And that is
the right solution I believe.

^ permalink raw reply	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2015-01-30  2:00 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2015-01-29  6:42 [PATCH] cpufreq: fix another race between PPC notification and vcpu_hotplug() Ethan Zhao
2015-01-29  8:38 ` Viresh Kumar
2015-01-29 21:14   ` santosh shilimkar
2015-01-30  1:44   ` ethan zhao
2015-01-30  2:00     ` Viresh Kumar

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