Re: [PATCH] power: genpd: fix lockdep issue for all subdomains

Re: [PATCH] power: genpd: fix lockdep issue for all subdomains

[Ulf Hansson]

+linux-pm, Daniel Kurtz, Nicolas Boichat

On 4 January 2016 at 11:39, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> During genpd_poweron, genpd->lock is acquired recursively for each
> parent (master) domain, which are separate obejcts. This confuses
> lockdep, which considers every operation on genpd->lock as being done on
> the same lock class. This leads to the following false positive warning:
>
> =============================================
> [ INFO: possible recursive locking detected ]
> 4.4.0-rc4-xu3s #32 Not tainted
> ---------------------------------------------
> swapper/0/1 is trying to acquire lock:
>  (&genpd->lock){+.+...}, at: [<c0361550>] __genpd_poweron+0x64/0x108
>
> but task is already holding lock:
>  (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8
>
> other info that might help us debug this:
>  Possible unsafe locking scenario:
>
>        CPU0
>        ----
>   lock(&genpd->lock);
>   lock(&genpd->lock);
>
>  *** DEADLOCK ***
>
>  May be due to missing lock nesting notation
>
> 3 locks held by swapper/0/1:
>  #0:  (&dev->mutex){......}, at: [<c0350910>] __driver_attach+0x48/0x98
>  #1:  (&dev->mutex){......}, at: [<c0350920>] __driver_attach+0x58/0x98
>  #2:  (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8
>
> stack backtrace:
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.0-rc4-xu3s #32
> Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
> [<c0016c98>] (unwind_backtrace) from [<c00139c4>] (show_stack+0x10/0x14)
> [<c00139c4>] (show_stack) from [<c0270df0>] (dump_stack+0x84/0xc4)
> [<c0270df0>] (dump_stack) from [<c00780b8>] (__lock_acquire+0x1f88/0x215c)
> [<c00780b8>] (__lock_acquire) from [<c007886c>] (lock_acquire+0xa4/0xd0)
> [<c007886c>] (lock_acquire) from [<c0641f2c>] (mutex_lock_nested+0x70/0x4d4)
> [<c0641f2c>] (mutex_lock_nested) from [<c0361550>] (__genpd_poweron+0x64/0x108)
> [<c0361550>] (__genpd_poweron) from [<c0361b00>] (genpd_dev_pm_attach+0x170/0x1b8)
> [<c0361b00>] (genpd_dev_pm_attach) from [<c03520a8>] (platform_drv_probe+0x2c/0xac)
> [<c03520a8>] (platform_drv_probe) from [<c03507d4>] (driver_probe_device+0x208/0x2fc)
> [<c03507d4>] (driver_probe_device) from [<c035095c>] (__driver_attach+0x94/0x98)
> [<c035095c>] (__driver_attach) from [<c034ec14>] (bus_for_each_dev+0x68/0x9c)
> [<c034ec14>] (bus_for_each_dev) from [<c034fec8>] (bus_add_driver+0x1a0/0x218)
> [<c034fec8>] (bus_add_driver) from [<c035115c>] (driver_register+0x78/0xf8)
> [<c035115c>] (driver_register) from [<c0338488>] (exynos_drm_register_drivers+0x28/0x74)
> [<c0338488>] (exynos_drm_register_drivers) from [<c0338594>] (exynos_drm_init+0x6c/0xc4)
> [<c0338594>] (exynos_drm_init) from [<c00097f4>] (do_one_initcall+0x90/0x1dc)
> [<c00097f4>] (do_one_initcall) from [<c0895e08>] (kernel_init_freeable+0x158/0x1f8)
> [<c0895e08>] (kernel_init_freeable) from [<c063ecac>] (kernel_init+0x8/0xe8)
> [<c063ecac>] (kernel_init) from [<c000f7d0>] (ret_from_fork+0x14/0x24)
>
> This patch replaces mutex_lock with mutex_lock_nested() and uses
> recursion depth to annotate each genpd->lock operation with separate
> lockdep subclass.
>
> Reported-by: Anand Moon <linux.amoon@gmail.com>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>

Thanks for looking into this!

Daniel Kurtz, did also run into this issue [1] and reported it a while ago.
There where some discussions and Daniel also posted a patch trying to
solve the issue [2]. That approach didn't work out, and unfortunate I
haven't yet been able to look closer into the issue. Sorry about that!

> ---
>  drivers/base/power/domain.c | 21 +++++++++++++--------
>  1 file changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
> index b803790..e02ddf6 100644
> --- a/drivers/base/power/domain.c
> +++ b/drivers/base/power/domain.c
> @@ -170,16 +170,15 @@ static void genpd_queue_power_off_work(struct generic_pm_domain *genpd)
>         queue_work(pm_wq, &genpd->power_off_work);
>  }
>
> -static int genpd_poweron(struct generic_pm_domain *genpd);
> -
>  /**
>   * __genpd_poweron - Restore power to a given PM domain and its masters.
>   * @genpd: PM domain to power up.
> + * @depth: nesting count for lockdep.
>   *
>   * Restore power to @genpd and all of its masters so that it is possible to
>   * resume a device belonging to it.
>   */
> -static int __genpd_poweron(struct generic_pm_domain *genpd)
> +static int __genpd_poweron(struct generic_pm_domain *genpd, unsigned int depth)
>  {
>         struct gpd_link *link;
>         int ret = 0;
> @@ -194,11 +193,16 @@ static int __genpd_poweron(struct generic_pm_domain *genpd)
>          * with it.
>          */
>         list_for_each_entry(link, &genpd->slave_links, slave_node) {
> -               genpd_sd_counter_inc(link->master);
> +               struct generic_pm_domain *master = link->master;
> +
> +               genpd_sd_counter_inc(master);
> +
> +               mutex_lock_nested(&master->lock, depth + 1);

Nested locks isn't a solution to a problem, but instead this tricks
lockdep about what goes on. Right?

I am wondering whether there's another option available which better
can instruct lockdep to not treat this as an error.

> +               ret = __genpd_poweron(master, depth + 1);
> +               mutex_unlock(&master->lock);
>
> -               ret = genpd_poweron(link->master);
>                 if (ret) {
> -                       genpd_sd_counter_dec(link->master);
> +                       genpd_sd_counter_dec(master);
>                         goto err;
>                 }
>         }
> @@ -230,11 +234,12 @@ static int genpd_poweron(struct generic_pm_domain *genpd)
>         int ret;
>
>         mutex_lock(&genpd->lock);
> -       ret = __genpd_poweron(genpd);
> +       ret = __genpd_poweron(genpd, 0);
>         mutex_unlock(&genpd->lock);
>         return ret;
>  }
>
> +
>  static int genpd_save_dev(struct generic_pm_domain *genpd, struct device *dev)
>  {
>         return GENPD_DEV_CALLBACK(genpd, int, save_state, dev);
> @@ -482,7 +487,7 @@ static int pm_genpd_runtime_resume(struct device *dev)
>         }
>
>         mutex_lock(&genpd->lock);
> -       ret = __genpd_poweron(genpd);
> +       ret = __genpd_poweron(genpd, 0);
>         mutex_unlock(&genpd->lock);
>
>         if (ret)
> --
> 1.9.2
>

Kind regards
Uffe

[1]
http://www.spinics.net/lists/arm-kernel/msg471025.html
[2]
http://www.spinics.net/lists/stable/msg113650.html

Re: [PATCH] power: genpd: fix lockdep issue for all subdomains

[Marek Szyprowski]

Hello,

On 2016-01-19 16:25, Ulf Hansson wrote:
> +linux-pm, Daniel Kurtz, Nicolas Boichat
>
> On 4 January 2016 at 11:39, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
>> During genpd_poweron, genpd->lock is acquired recursively for each
>> parent (master) domain, which are separate obejcts. This confuses
>> lockdep, which considers every operation on genpd->lock as being done on
>> the same lock class. This leads to the following false positive warning:
>>
>> =============================================
>> [ INFO: possible recursive locking detected ]
>> 4.4.0-rc4-xu3s #32 Not tainted
>> ---------------------------------------------
>> swapper/0/1 is trying to acquire lock:
>>   (&genpd->lock){+.+...}, at: [<c0361550>] __genpd_poweron+0x64/0x108
>>
>> but task is already holding lock:
>>   (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8
>>
>> other info that might help us debug this:
>>   Possible unsafe locking scenario:
>>
>>         CPU0
>>         ----
>>    lock(&genpd->lock);
>>    lock(&genpd->lock);
>>
>>   *** DEADLOCK ***
>>
>>   May be due to missing lock nesting notation
>>
>> 3 locks held by swapper/0/1:
>>   #0:  (&dev->mutex){......}, at: [<c0350910>] __driver_attach+0x48/0x98
>>   #1:  (&dev->mutex){......}, at: [<c0350920>] __driver_attach+0x58/0x98
>>   #2:  (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8
>>
>> stack backtrace:
>> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.0-rc4-xu3s #32
>> Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
>> [<c0016c98>] (unwind_backtrace) from [<c00139c4>] (show_stack+0x10/0x14)
>> [<c00139c4>] (show_stack) from [<c0270df0>] (dump_stack+0x84/0xc4)
>> [<c0270df0>] (dump_stack) from [<c00780b8>] (__lock_acquire+0x1f88/0x215c)
>> [<c00780b8>] (__lock_acquire) from [<c007886c>] (lock_acquire+0xa4/0xd0)
>> [<c007886c>] (lock_acquire) from [<c0641f2c>] (mutex_lock_nested+0x70/0x4d4)
>> [<c0641f2c>] (mutex_lock_nested) from [<c0361550>] (__genpd_poweron+0x64/0x108)
>> [<c0361550>] (__genpd_poweron) from [<c0361b00>] (genpd_dev_pm_attach+0x170/0x1b8)
>> [<c0361b00>] (genpd_dev_pm_attach) from [<c03520a8>] (platform_drv_probe+0x2c/0xac)
>> [<c03520a8>] (platform_drv_probe) from [<c03507d4>] (driver_probe_device+0x208/0x2fc)
>> [<c03507d4>] (driver_probe_device) from [<c035095c>] (__driver_attach+0x94/0x98)
>> [<c035095c>] (__driver_attach) from [<c034ec14>] (bus_for_each_dev+0x68/0x9c)
>> [<c034ec14>] (bus_for_each_dev) from [<c034fec8>] (bus_add_driver+0x1a0/0x218)
>> [<c034fec8>] (bus_add_driver) from [<c035115c>] (driver_register+0x78/0xf8)
>> [<c035115c>] (driver_register) from [<c0338488>] (exynos_drm_register_drivers+0x28/0x74)
>> [<c0338488>] (exynos_drm_register_drivers) from [<c0338594>] (exynos_drm_init+0x6c/0xc4)
>> [<c0338594>] (exynos_drm_init) from [<c00097f4>] (do_one_initcall+0x90/0x1dc)
>> [<c00097f4>] (do_one_initcall) from [<c0895e08>] (kernel_init_freeable+0x158/0x1f8)
>> [<c0895e08>] (kernel_init_freeable) from [<c063ecac>] (kernel_init+0x8/0xe8)
>> [<c063ecac>] (kernel_init) from [<c000f7d0>] (ret_from_fork+0x14/0x24)
>>
>> This patch replaces mutex_lock with mutex_lock_nested() and uses
>> recursion depth to annotate each genpd->lock operation with separate
>> lockdep subclass.
>>
>> Reported-by: Anand Moon <linux.amoon@gmail.com>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Thanks for looking into this!
>
> Daniel Kurtz, did also run into this issue [1] and reported it a while ago.
> There where some discussions and Daniel also posted a patch trying to
> solve the issue [2]. That approach didn't work out, and unfortunate I
> haven't yet been able to look closer into the issue. Sorry about that!
>
>> ---
>>   drivers/base/power/domain.c | 21 +++++++++++++--------
>>   1 file changed, 13 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
>> index b803790..e02ddf6 100644
>> --- a/drivers/base/power/domain.c
>> +++ b/drivers/base/power/domain.c
>> @@ -170,16 +170,15 @@ static void genpd_queue_power_off_work(struct generic_pm_domain *genpd)
>>          queue_work(pm_wq, &genpd->power_off_work);
>>   }
>>
>> -static int genpd_poweron(struct generic_pm_domain *genpd);
>> -
>>   /**
>>    * __genpd_poweron - Restore power to a given PM domain and its masters.
>>    * @genpd: PM domain to power up.
>> + * @depth: nesting count for lockdep.
>>    *
>>    * Restore power to @genpd and all of its masters so that it is possible to
>>    * resume a device belonging to it.
>>    */
>> -static int __genpd_poweron(struct generic_pm_domain *genpd)
>> +static int __genpd_poweron(struct generic_pm_domain *genpd, unsigned int depth)
>>   {
>>          struct gpd_link *link;
>>          int ret = 0;
>> @@ -194,11 +193,16 @@ static int __genpd_poweron(struct generic_pm_domain *genpd)
>>           * with it.
>>           */
>>          list_for_each_entry(link, &genpd->slave_links, slave_node) {
>> -               genpd_sd_counter_inc(link->master);
>> +               struct generic_pm_domain *master = link->master;
>> +
>> +               genpd_sd_counter_inc(master);
>> +
>> +               mutex_lock_nested(&master->lock, depth + 1);
> Nested locks isn't a solution to a problem, but instead this tricks
> lockdep about what goes on. Right?

The only difference between mutex_lock_nested and mutex_lock is the way
it is interpreted by deplock. The additional argument is deplock subclass
of the lock. The name of this function is imho a bit misleading.

> I am wondering whether there's another option available which better
> can instruct lockdep to not treat this as an error.

Similar solution is already applied in regulators and i2c cores, see
regulator_lock_supply() and i2c_del_adapter() functions.

>> +               ret = __genpd_poweron(master, depth + 1);
>> +               mutex_unlock(&master->lock);
>>
>> -               ret = genpd_poweron(link->master);
>>                  if (ret) {
>> -                       genpd_sd_counter_dec(link->master);
>> +                       genpd_sd_counter_dec(master);
>>                          goto err;
>>                  }
>>          }
>> @@ -230,11 +234,12 @@ static int genpd_poweron(struct generic_pm_domain *genpd)
>>          int ret;
>>
>>          mutex_lock(&genpd->lock);
>> -       ret = __genpd_poweron(genpd);
>> +       ret = __genpd_poweron(genpd, 0);
>>          mutex_unlock(&genpd->lock);
>>          return ret;
>>   }
>>
>> +
>>   static int genpd_save_dev(struct generic_pm_domain *genpd, struct device *dev)
>>   {
>>          return GENPD_DEV_CALLBACK(genpd, int, save_state, dev);
>> @@ -482,7 +487,7 @@ static int pm_genpd_runtime_resume(struct device *dev)
>>          }
>>
>>          mutex_lock(&genpd->lock);
>> -       ret = __genpd_poweron(genpd);
>> +       ret = __genpd_poweron(genpd, 0);
>>          mutex_unlock(&genpd->lock);
>>
>>          if (ret)
>> --
>> 1.9.2
>>
> Kind regards
> Uffe
>
> [1]
> http://www.spinics.net/lists/arm-kernel/msg471025.html
> [2]
> http://www.spinics.net/lists/stable/msg113650.html
>
>

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland

Re: [PATCH] power: genpd: fix lockdep issue for all subdomains

[Ulf Hansson]

[...]

>>> During genpd_poweron, genpd->lock is acquired recursively for each
>>> parent (master) domain, which are separate obejcts. This confuses
>>> lockdep, which considers every operation on genpd->lock as being done on
>>> the same lock class. This leads to the following false positive warning:
>>>
>>> =============================================
>>> [ INFO: possible recursive locking detected ]
>>> 4.4.0-rc4-xu3s #32 Not tainted
>>> ---------------------------------------------
>>> swapper/0/1 is trying to acquire lock:
>>>   (&genpd->lock){+.+...}, at: [<c0361550>] __genpd_poweron+0x64/0x108
>>>
>>> but task is already holding lock:
>>>   (&genpd->lock){+.+...}, at: [<c0361af8>]
>>> genpd_dev_pm_attach+0x168/0x1b8
>>>
>>> other info that might help us debug this:
>>>   Possible unsafe locking scenario:
>>>
>>>         CPU0
>>>         ----
>>>    lock(&genpd->lock);
>>>    lock(&genpd->lock);
>>>
>>>   *** DEADLOCK ***
>>>
>>>   May be due to missing lock nesting notation
>>>
>>> 3 locks held by swapper/0/1:
>>>   #0:  (&dev->mutex){......}, at: [<c0350910>] __driver_attach+0x48/0x98
>>>   #1:  (&dev->mutex){......}, at: [<c0350920>] __driver_attach+0x58/0x98
>>>   #2:  (&genpd->lock){+.+...}, at: [<c0361af8>]
>>> genpd_dev_pm_attach+0x168/0x1b8
>>>
>>> stack backtrace:
>>> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.0-rc4-xu3s #32
>>> Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
>>> [<c0016c98>] (unwind_backtrace) from [<c00139c4>] (show_stack+0x10/0x14)
>>> [<c00139c4>] (show_stack) from [<c0270df0>] (dump_stack+0x84/0xc4)
>>> [<c0270df0>] (dump_stack) from [<c00780b8>]
>>> (__lock_acquire+0x1f88/0x215c)
>>> [<c00780b8>] (__lock_acquire) from [<c007886c>] (lock_acquire+0xa4/0xd0)
>>> [<c007886c>] (lock_acquire) from [<c0641f2c>]
>>> (mutex_lock_nested+0x70/0x4d4)
>>> [<c0641f2c>] (mutex_lock_nested) from [<c0361550>]
>>> (__genpd_poweron+0x64/0x108)
>>> [<c0361550>] (__genpd_poweron) from [<c0361b00>]
>>> (genpd_dev_pm_attach+0x170/0x1b8)
>>> [<c0361b00>] (genpd_dev_pm_attach) from [<c03520a8>]
>>> (platform_drv_probe+0x2c/0xac)
>>> [<c03520a8>] (platform_drv_probe) from [<c03507d4>]
>>> (driver_probe_device+0x208/0x2fc)
>>> [<c03507d4>] (driver_probe_device) from [<c035095c>]
>>> (__driver_attach+0x94/0x98)
>>> [<c035095c>] (__driver_attach) from [<c034ec14>]
>>> (bus_for_each_dev+0x68/0x9c)
>>> [<c034ec14>] (bus_for_each_dev) from [<c034fec8>]
>>> (bus_add_driver+0x1a0/0x218)
>>> [<c034fec8>] (bus_add_driver) from [<c035115c>]
>>> (driver_register+0x78/0xf8)
>>> [<c035115c>] (driver_register) from [<c0338488>]
>>> (exynos_drm_register_drivers+0x28/0x74)
>>> [<c0338488>] (exynos_drm_register_drivers) from [<c0338594>]
>>> (exynos_drm_init+0x6c/0xc4)
>>> [<c0338594>] (exynos_drm_init) from [<c00097f4>]
>>> (do_one_initcall+0x90/0x1dc)
>>> [<c00097f4>] (do_one_initcall) from [<c0895e08>]
>>> (kernel_init_freeable+0x158/0x1f8)
>>> [<c0895e08>] (kernel_init_freeable) from [<c063ecac>]
>>> (kernel_init+0x8/0xe8)
>>> [<c063ecac>] (kernel_init) from [<c000f7d0>] (ret_from_fork+0x14/0x24)
>>>
>>> This patch replaces mutex_lock with mutex_lock_nested() and uses
>>> recursion depth to annotate each genpd->lock operation with separate
>>> lockdep subclass.
>>>
>>> Reported-by: Anand Moon <linux.amoon@gmail.com>
>>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>>

Acked-by: Ulf Hansson <ulf.hansson@linaro.org>

You didn't send this to linux-pm so probably you should resend it, so
Rafael can pick it up.

[...]

>
> The only difference between mutex_lock_nested and mutex_lock is the way
> it is interpreted by deplock. The additional argument is deplock subclass
> of the lock. The name of this function is imho a bit misleading.

:-) Of course you are absolutely right. Thanks!

[...]

Kind regards
Uffe

[PATCH RESEND] power: genpd: fix lockdep issue for all subdomains

[Marek Szyprowski]

During genpd_poweron, genpd->lock is acquired recursively for each
parent (master) domain, which are separate objects. This confuses
lockdep, which considers every operation on genpd->lock as being done on
the same lock class. This leads to the following false positive warning:

=============================================
[ INFO: possible recursive locking detected ]
4.4.0-rc4-xu3s #32 Not tainted
---------------------------------------------
swapper/0/1 is trying to acquire lock:
 (&genpd->lock){+.+...}, at: [<c0361550>] __genpd_poweron+0x64/0x108

but task is already holding lock:
 (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&genpd->lock);
  lock(&genpd->lock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by swapper/0/1:
 #0:  (&dev->mutex){......}, at: [<c0350910>] __driver_attach+0x48/0x98
 #1:  (&dev->mutex){......}, at: [<c0350920>] __driver_attach+0x58/0x98
 #2:  (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8

stack backtrace:
CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.0-rc4-xu3s #32
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[<c0016c98>] (unwind_backtrace) from [<c00139c4>] (show_stack+0x10/0x14)
[<c00139c4>] (show_stack) from [<c0270df0>] (dump_stack+0x84/0xc4)
[<c0270df0>] (dump_stack) from [<c00780b8>] (__lock_acquire+0x1f88/0x215c)
[<c00780b8>] (__lock_acquire) from [<c007886c>] (lock_acquire+0xa4/0xd0)
[<c007886c>] (lock_acquire) from [<c0641f2c>] (mutex_lock_nested+0x70/0x4d4)
[<c0641f2c>] (mutex_lock_nested) from [<c0361550>] (__genpd_poweron+0x64/0x108)
[<c0361550>] (__genpd_poweron) from [<c0361b00>] (genpd_dev_pm_attach+0x170/0x1b8)
[<c0361b00>] (genpd_dev_pm_attach) from [<c03520a8>] (platform_drv_probe+0x2c/0xac)
[<c03520a8>] (platform_drv_probe) from [<c03507d4>] (driver_probe_device+0x208/0x2fc)
[<c03507d4>] (driver_probe_device) from [<c035095c>] (__driver_attach+0x94/0x98)
[<c035095c>] (__driver_attach) from [<c034ec14>] (bus_for_each_dev+0x68/0x9c)
[<c034ec14>] (bus_for_each_dev) from [<c034fec8>] (bus_add_driver+0x1a0/0x218)
[<c034fec8>] (bus_add_driver) from [<c035115c>] (driver_register+0x78/0xf8)
[<c035115c>] (driver_register) from [<c0338488>] (exynos_drm_register_drivers+0x28/0x74)
[<c0338488>] (exynos_drm_register_drivers) from [<c0338594>] (exynos_drm_init+0x6c/0xc4)
[<c0338594>] (exynos_drm_init) from [<c00097f4>] (do_one_initcall+0x90/0x1dc)
[<c00097f4>] (do_one_initcall) from [<c0895e08>] (kernel_init_freeable+0x158/0x1f8)
[<c0895e08>] (kernel_init_freeable) from [<c063ecac>] (kernel_init+0x8/0xe8)
[<c063ecac>] (kernel_init) from [<c000f7d0>] (ret_from_fork+0x14/0x24)

This patch replaces mutex_lock with mutex_lock_nested() and uses
recursion depth to annotate each genpd->lock operation with separate
lockdep subclass.

Reported-by: Anand Moon <linux.amoon@gmail.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Anand Moon <linux.amoon@gmail.com>
Tested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
---
 drivers/base/power/domain.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index b803790..e02ddf6 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -170,16 +170,15 @@ static void genpd_queue_power_off_work(struct generic_pm_domain *genpd)
 	queue_work(pm_wq, &genpd->power_off_work);
 }
 
-static int genpd_poweron(struct generic_pm_domain *genpd);
-
 /**
  * __genpd_poweron - Restore power to a given PM domain and its masters.
  * @genpd: PM domain to power up.
+ * @depth: nesting count for lockdep.
  *
  * Restore power to @genpd and all of its masters so that it is possible to
  * resume a device belonging to it.
  */
-static int __genpd_poweron(struct generic_pm_domain *genpd)
+static int __genpd_poweron(struct generic_pm_domain *genpd, unsigned int depth)
 {
 	struct gpd_link *link;
 	int ret = 0;
@@ -194,11 +193,16 @@ static int __genpd_poweron(struct generic_pm_domain *genpd)
 	 * with it.
 	 */
 	list_for_each_entry(link, &genpd->slave_links, slave_node) {
-		genpd_sd_counter_inc(link->master);
+		struct generic_pm_domain *master = link->master;
+
+		genpd_sd_counter_inc(master);
+
+		mutex_lock_nested(&master->lock, depth + 1);
+		ret = __genpd_poweron(master, depth + 1);
+		mutex_unlock(&master->lock);
 
-		ret = genpd_poweron(link->master);
 		if (ret) {
-			genpd_sd_counter_dec(link->master);
+			genpd_sd_counter_dec(master);
 			goto err;
 		}
 	}
@@ -230,11 +234,12 @@ static int genpd_poweron(struct generic_pm_domain *genpd)
 	int ret;
 
 	mutex_lock(&genpd->lock);
-	ret = __genpd_poweron(genpd);
+	ret = __genpd_poweron(genpd, 0);
 	mutex_unlock(&genpd->lock);
 	return ret;
 }
 
+
 static int genpd_save_dev(struct generic_pm_domain *genpd, struct device *dev)
 {
 	return GENPD_DEV_CALLBACK(genpd, int, save_state, dev);
@@ -482,7 +487,7 @@ static int pm_genpd_runtime_resume(struct device *dev)
 	}
 
 	mutex_lock(&genpd->lock);
-	ret = __genpd_poweron(genpd);
+	ret = __genpd_poweron(genpd, 0);
 	mutex_unlock(&genpd->lock);
 
 	if (ret)
-- 
1.9.2

Re: [PATCH RESEND] power: genpd: fix lockdep issue for all subdomains

[Ulf Hansson]

On 20 January 2016 at 10:13, Marek Szyprowski <m.szyprowski@samsung.com> wrote:
> During genpd_poweron, genpd->lock is acquired recursively for each
> parent (master) domain, which are separate objects. This confuses
> lockdep, which considers every operation on genpd->lock as being done on
> the same lock class. This leads to the following false positive warning:
>
> =============================================
> [ INFO: possible recursive locking detected ]
> 4.4.0-rc4-xu3s #32 Not tainted
> ---------------------------------------------
> swapper/0/1 is trying to acquire lock:
>  (&genpd->lock){+.+...}, at: [<c0361550>] __genpd_poweron+0x64/0x108
>
> but task is already holding lock:
>  (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8
>
> other info that might help us debug this:
>  Possible unsafe locking scenario:
>
>        CPU0
>        ----
>   lock(&genpd->lock);
>   lock(&genpd->lock);
>
>  *** DEADLOCK ***
>
>  May be due to missing lock nesting notation
>
> 3 locks held by swapper/0/1:
>  #0:  (&dev->mutex){......}, at: [<c0350910>] __driver_attach+0x48/0x98
>  #1:  (&dev->mutex){......}, at: [<c0350920>] __driver_attach+0x58/0x98
>  #2:  (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8
>
> stack backtrace:
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.0-rc4-xu3s #32
> Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
> [<c0016c98>] (unwind_backtrace) from [<c00139c4>] (show_stack+0x10/0x14)
> [<c00139c4>] (show_stack) from [<c0270df0>] (dump_stack+0x84/0xc4)
> [<c0270df0>] (dump_stack) from [<c00780b8>] (__lock_acquire+0x1f88/0x215c)
> [<c00780b8>] (__lock_acquire) from [<c007886c>] (lock_acquire+0xa4/0xd0)
> [<c007886c>] (lock_acquire) from [<c0641f2c>] (mutex_lock_nested+0x70/0x4d4)
> [<c0641f2c>] (mutex_lock_nested) from [<c0361550>] (__genpd_poweron+0x64/0x108)
> [<c0361550>] (__genpd_poweron) from [<c0361b00>] (genpd_dev_pm_attach+0x170/0x1b8)
> [<c0361b00>] (genpd_dev_pm_attach) from [<c03520a8>] (platform_drv_probe+0x2c/0xac)
> [<c03520a8>] (platform_drv_probe) from [<c03507d4>] (driver_probe_device+0x208/0x2fc)
> [<c03507d4>] (driver_probe_device) from [<c035095c>] (__driver_attach+0x94/0x98)
> [<c035095c>] (__driver_attach) from [<c034ec14>] (bus_for_each_dev+0x68/0x9c)
> [<c034ec14>] (bus_for_each_dev) from [<c034fec8>] (bus_add_driver+0x1a0/0x218)
> [<c034fec8>] (bus_add_driver) from [<c035115c>] (driver_register+0x78/0xf8)
> [<c035115c>] (driver_register) from [<c0338488>] (exynos_drm_register_drivers+0x28/0x74)
> [<c0338488>] (exynos_drm_register_drivers) from [<c0338594>] (exynos_drm_init+0x6c/0xc4)
> [<c0338594>] (exynos_drm_init) from [<c00097f4>] (do_one_initcall+0x90/0x1dc)
> [<c00097f4>] (do_one_initcall) from [<c0895e08>] (kernel_init_freeable+0x158/0x1f8)
> [<c0895e08>] (kernel_init_freeable) from [<c063ecac>] (kernel_init+0x8/0xe8)
> [<c063ecac>] (kernel_init) from [<c000f7d0>] (ret_from_fork+0x14/0x24)
>
> This patch replaces mutex_lock with mutex_lock_nested() and uses
> recursion depth to annotate each genpd->lock operation with separate
> lockdep subclass.
>
> Reported-by: Anand Moon <linux.amoon@gmail.com>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Tested-by: Anand Moon <linux.amoon@gmail.com>
> Tested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
> Acked-by: Ulf Hansson <ulf.hansson@linaro.org>

To be consistent with earlier changes, I would prefer to have the
prefix of the commit message header to "PM / Domains:".

Although you can likely leave that to be amended by Rafael, if he also
thinks it's good idea.

Kind regards
Uffe

Re: [PATCH RESEND] power: genpd: fix lockdep issue for all subdomains

[Rafael J. Wysocki]

On Wednesday, January 20, 2016 10:13:42 AM Marek Szyprowski wrote:
> During genpd_poweron, genpd->lock is acquired recursively for each
> parent (master) domain, which are separate objects. This confuses
> lockdep, which considers every operation on genpd->lock as being done on
> the same lock class. This leads to the following false positive warning:
> 
> =============================================
> [ INFO: possible recursive locking detected ]
> 4.4.0-rc4-xu3s #32 Not tainted
> ---------------------------------------------
> swapper/0/1 is trying to acquire lock:
>  (&genpd->lock){+.+...}, at: [<c0361550>] __genpd_poweron+0x64/0x108
> 
> but task is already holding lock:
>  (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8
> 
> other info that might help us debug this:
>  Possible unsafe locking scenario:
> 
>        CPU0
>        ----
>   lock(&genpd->lock);
>   lock(&genpd->lock);
> 
>  *** DEADLOCK ***
> 
>  May be due to missing lock nesting notation
> 
> 3 locks held by swapper/0/1:
>  #0:  (&dev->mutex){......}, at: [<c0350910>] __driver_attach+0x48/0x98
>  #1:  (&dev->mutex){......}, at: [<c0350920>] __driver_attach+0x58/0x98
>  #2:  (&genpd->lock){+.+...}, at: [<c0361af8>] genpd_dev_pm_attach+0x168/0x1b8
> 
> stack backtrace:
> CPU: 0 PID: 1 Comm: swapper/0 Not tainted 4.4.0-rc4-xu3s #32
> Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
> [<c0016c98>] (unwind_backtrace) from [<c00139c4>] (show_stack+0x10/0x14)
> [<c00139c4>] (show_stack) from [<c0270df0>] (dump_stack+0x84/0xc4)
> [<c0270df0>] (dump_stack) from [<c00780b8>] (__lock_acquire+0x1f88/0x215c)
> [<c00780b8>] (__lock_acquire) from [<c007886c>] (lock_acquire+0xa4/0xd0)
> [<c007886c>] (lock_acquire) from [<c0641f2c>] (mutex_lock_nested+0x70/0x4d4)
> [<c0641f2c>] (mutex_lock_nested) from [<c0361550>] (__genpd_poweron+0x64/0x108)
> [<c0361550>] (__genpd_poweron) from [<c0361b00>] (genpd_dev_pm_attach+0x170/0x1b8)
> [<c0361b00>] (genpd_dev_pm_attach) from [<c03520a8>] (platform_drv_probe+0x2c/0xac)
> [<c03520a8>] (platform_drv_probe) from [<c03507d4>] (driver_probe_device+0x208/0x2fc)
> [<c03507d4>] (driver_probe_device) from [<c035095c>] (__driver_attach+0x94/0x98)
> [<c035095c>] (__driver_attach) from [<c034ec14>] (bus_for_each_dev+0x68/0x9c)
> [<c034ec14>] (bus_for_each_dev) from [<c034fec8>] (bus_add_driver+0x1a0/0x218)
> [<c034fec8>] (bus_add_driver) from [<c035115c>] (driver_register+0x78/0xf8)
> [<c035115c>] (driver_register) from [<c0338488>] (exynos_drm_register_drivers+0x28/0x74)
> [<c0338488>] (exynos_drm_register_drivers) from [<c0338594>] (exynos_drm_init+0x6c/0xc4)
> [<c0338594>] (exynos_drm_init) from [<c00097f4>] (do_one_initcall+0x90/0x1dc)
> [<c00097f4>] (do_one_initcall) from [<c0895e08>] (kernel_init_freeable+0x158/0x1f8)
> [<c0895e08>] (kernel_init_freeable) from [<c063ecac>] (kernel_init+0x8/0xe8)
> [<c063ecac>] (kernel_init) from [<c000f7d0>] (ret_from_fork+0x14/0x24)
> 
> This patch replaces mutex_lock with mutex_lock_nested() and uses
> recursion depth to annotate each genpd->lock operation with separate
> lockdep subclass.
> 
> Reported-by: Anand Moon <linux.amoon@gmail.com>
> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> Tested-by: Anand Moon <linux.amoon@gmail.com>
> Tested-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
> Acked-by: Ulf Hansson <ulf.hansson@linaro.org>

Applied (with a minor subject change), thanks!

Rafael