[PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

[PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

[Anand Moon]

From: Anand Moon <linux.amoon@gmail.com>

pl330_tasklet tasklet uses the same spinlock pch->lock for safe IRQ locking.
It's safe to initialize pl330_tasklet tasklet after release of the locking.

Signed-off-by: Anand Moon <linux.amoon@gmail.com>
---
 drivers/dma/pl330.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
index 17ee758..df2cab1 100644
--- a/drivers/dma/pl330.c
+++ b/drivers/dma/pl330.c
@@ -2091,10 +2091,10 @@ static int pl330_alloc_chan_resources(struct dma_chan *chan)
 		return -ENOMEM;
 	}
 
-	tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
-
 	spin_unlock_irqrestore(&pch->lock, flags);
 
+	tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
+
 	return 1;
 }
 
-- 
1.9.1

Re: [PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

[Krzysztof Kozlowski]

2016-02-19 2:21 GMT+09:00 Anand Moon <linux.amoon@gmail.com>:
> From: Anand Moon <linux.amoon@gmail.com>
>
> pl330_tasklet tasklet uses the same spinlock pch->lock for safe IRQ locking.
> It's safe to initialize pl330_tasklet tasklet after release of the locking.

This is tasklet init, not tasklet execution (which you are referring
to in first sentence). I don't get how usage of spinlock during
execution guarantees the safeness during init... Please describe why
this is safe.

Best regards,
Krzysztof

>
> Signed-off-by: Anand Moon <linux.amoon@gmail.com>
> ---
>  drivers/dma/pl330.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
> index 17ee758..df2cab1 100644
> --- a/drivers/dma/pl330.c
> +++ b/drivers/dma/pl330.c
> @@ -2091,10 +2091,10 @@ static int pl330_alloc_chan_resources(struct dma_chan *chan)
>                 return -ENOMEM;
>         }
>
> -       tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
> -
>         spin_unlock_irqrestore(&pch->lock, flags);
>
> +       tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
> +
>         return 1;
>  }
>
> --
> 1.9.1
>
> --
> To unsubscribe from this list: send the line "unsubscribe dmaengine" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

[Anand Moon]

Hi Krzysztof,

On 19 February 2016 at 11:36, Krzysztof Kozlowski
<k.kozlowski@samsung.com> wrote:
> 2016-02-19 2:21 GMT+09:00 Anand Moon <linux.amoon@gmail.com>:
>> From: Anand Moon <linux.amoon@gmail.com>
>>
>> pl330_tasklet tasklet uses the same spinlock pch->lock for safe IRQ locking.
>> It's safe to initialize pl330_tasklet tasklet after release of the locking.
>
> This is tasklet init, not tasklet execution (which you are referring
> to in first sentence). I don't get how usage of spinlock during
> execution guarantees the safeness during init... Please describe why
> this is safe.
>
> Best regards,
> Krzysztof
>

http://lxr.free-electrons.com/source/drivers/dma/pl330.c#L1972

pl330_tasklet function which is initiated by tasklet_init is trying to lock
using same spin_unlock_irqsave/restore pch->lock.
So better release the pch->lock and then initialize  the tasklet_init.

Best Regards,
-Anand Moon

>>
>> Signed-off-by: Anand Moon <linux.amoon@gmail.com>
>> ---
>>  drivers/dma/pl330.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
>> index 17ee758..df2cab1 100644
>> --- a/drivers/dma/pl330.c
>> +++ b/drivers/dma/pl330.c
>> @@ -2091,10 +2091,10 @@ static int pl330_alloc_chan_resources(struct dma_chan *chan)
>>                 return -ENOMEM;
>>         }
>>
>> -       tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
>> -
>>         spin_unlock_irqrestore(&pch->lock, flags);
>>
>> +       tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
>> +
>>         return 1;
>>  }
>>
>> --
>> 1.9.1
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe dmaengine" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

[Krzysztof Kozlowski]

On 19.02.2016 15:39, Anand Moon wrote:
> Hi Krzysztof,
> 
> On 19 February 2016 at 11:36, Krzysztof Kozlowski
> <k.kozlowski@samsung.com> wrote:
>> 2016-02-19 2:21 GMT+09:00 Anand Moon <linux.amoon@gmail.com>:
>>> From: Anand Moon <linux.amoon@gmail.com>
>>>
>>> pl330_tasklet tasklet uses the same spinlock pch->lock for safe IRQ locking.
>>> It's safe to initialize pl330_tasklet tasklet after release of the locking.
>>
>> This is tasklet init, not tasklet execution (which you are referring
>> to in first sentence). I don't get how usage of spinlock during
>> execution guarantees the safeness during init... Please describe why
>> this is safe.
>>
>> Best regards,
>> Krzysztof
>>
> 
> http://lxr.free-electrons.com/source/drivers/dma/pl330.c#L1972
> 
> pl330_tasklet function which is initiated by tasklet_init is trying to lock
> using same spin_unlock_irqsave/restore pch->lock.

tasklet_init does not call pl330_tasklet (if this is what you mean by
"initiated"). What is the correlation? Why are you referring to the
locks in pl330_tasklet?

> So better release the pch->lock and then initialize  the tasklet_init.

Why "better"?

Best regards,
Krzysztof

> 
>>>
>>> Signed-off-by: Anand Moon <linux.amoon@gmail.com>
>>> ---
>>>  drivers/dma/pl330.c | 4 ++--
>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
>>> index 17ee758..df2cab1 100644
>>> --- a/drivers/dma/pl330.c
>>> +++ b/drivers/dma/pl330.c
>>> @@ -2091,10 +2091,10 @@ static int pl330_alloc_chan_resources(struct dma_chan *chan)
>>>                 return -ENOMEM;
>>>         }
>>>
>>> -       tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
>>> -
>>>         spin_unlock_irqrestore(&pch->lock, flags);
>>>
>>> +       tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
>>> +
>>>         return 1;
>>>  }
>>>
>>> --
>>> 1.9.1
>>>
>>> --
>>> To unsubscribe from this list: send the line "unsubscribe dmaengine" in
>>> the body of a message to majordomo@vger.kernel.org
>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> 
> 

Re: [PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

[Anand Moon]

Hi Krzysztof,

On 19 February 2016 at 12:50, Krzysztof Kozlowski
<k.kozlowski@samsung.com> wrote:
> On 19.02.2016 15:39, Anand Moon wrote:
>> Hi Krzysztof,
>>
>> On 19 February 2016 at 11:36, Krzysztof Kozlowski
>> <k.kozlowski@samsung.com> wrote:
>>> 2016-02-19 2:21 GMT+09:00 Anand Moon <linux.amoon@gmail.com>:
>>>> From: Anand Moon <linux.amoon@gmail.com>
>>>>
>>>> pl330_tasklet tasklet uses the same spinlock pch->lock for safe IRQ locking.
>>>> It's safe to initialize pl330_tasklet tasklet after release of the locking.
>>>
>>> This is tasklet init, not tasklet execution (which you are referring
>>> to in first sentence). I don't get how usage of spinlock during
>>> execution guarantees the safeness during init... Please describe why
>>> this is safe.
>>>
>>> Best regards,
>>> Krzysztof
>>>
>>
>> http://lxr.free-electrons.com/source/drivers/dma/pl330.c#L1972
>>
>> pl330_tasklet function which is initiated by tasklet_init is trying to lock
>> using same spin_unlock_irqsave/restore pch->lock.
>
> tasklet_init does not call pl330_tasklet (if this is what you mean by
> "initiated"). What is the correlation? Why are you referring to the
> locks in pl330_tasklet?
>
>> So better release the pch->lock and then initialize  the tasklet_init.
>
> Why "better"?
>
> Best regards,
> Krzysztof
>

On SMP arch, tasklet_init could spawn the pl330_tasklet routine,
it could be any CPU which could take up this task.
So just for good timing of Initialization of the pl330_tasklet after
spin_unlock_irqrestore.
That is what I can figure out.

My choice of words could be a problem.

Best regards,
-Anand Moon

>>
>>>>
>>>> Signed-off-by: Anand Moon <linux.amoon@gmail.com>
>>>> ---
>>>>  drivers/dma/pl330.c | 4 ++--
>>>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/dma/pl330.c b/drivers/dma/pl330.c
>>>> index 17ee758..df2cab1 100644
>>>> --- a/drivers/dma/pl330.c
>>>> +++ b/drivers/dma/pl330.c
>>>> @@ -2091,10 +2091,10 @@ static int pl330_alloc_chan_resources(struct dma_chan *chan)
>>>>                 return -ENOMEM;
>>>>         }
>>>>
>>>> -       tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
>>>> -
>>>>         spin_unlock_irqrestore(&pch->lock, flags);
>>>>
>>>> +       tasklet_init(&pch->task, pl330_tasklet, (unsigned long) pch);
>>>> +
>>>>         return 1;
>>>>  }
>>>>
>>>> --
>>>> 1.9.1
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe dmaengine" in
>>>> the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
>>
>

Re: [PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

[Lars-Peter Clausen]

On 02/19/2016 09:10 AM, Anand Moon wrote:
> Hi Krzysztof,
> 
> On 19 February 2016 at 12:50, Krzysztof Kozlowski
> <k.kozlowski@samsung.com> wrote:
>> On 19.02.2016 15:39, Anand Moon wrote:
>>> Hi Krzysztof,
>>>
>>> On 19 February 2016 at 11:36, Krzysztof Kozlowski
>>> <k.kozlowski@samsung.com> wrote:
>>>> 2016-02-19 2:21 GMT+09:00 Anand Moon <linux.amoon@gmail.com>:
>>>>> From: Anand Moon <linux.amoon@gmail.com>
>>>>>
>>>>> pl330_tasklet tasklet uses the same spinlock pch->lock for safe IRQ locking.
>>>>> It's safe to initialize pl330_tasklet tasklet after release of the locking.
>>>>
>>>> This is tasklet init, not tasklet execution (which you are referring
>>>> to in first sentence). I don't get how usage of spinlock during
>>>> execution guarantees the safeness during init... Please describe why
>>>> this is safe.
>>>>
>>>> Best regards,
>>>> Krzysztof
>>>>
>>>
>>> http://lxr.free-electrons.com/source/drivers/dma/pl330.c#L1972
>>>
>>> pl330_tasklet function which is initiated by tasklet_init is trying to lock
>>> using same spin_unlock_irqsave/restore pch->lock.
>>
>> tasklet_init does not call pl330_tasklet (if this is what you mean by
>> "initiated"). What is the correlation? Why are you referring to the
>> locks in pl330_tasklet?
>>
>>> So better release the pch->lock and then initialize  the tasklet_init.
>>
>> Why "better"?
>>
>> Best regards,
>> Krzysztof
>>
> 
> On SMP arch, tasklet_init could spawn the pl330_tasklet routine,
> it could be any CPU which could take up this task.
> So just for good timing of Initialization of the pl330_tasklet after
> spin_unlock_irqrestore.
> That is what I can figure out.

Hi,

tasklet_init() does not spwan the tasklet function, tasklet_schedule() does
that.

But there is still room for optimization here. If you want to move the
tasklet_init() call please move it into pl330_probe() next to where the
channel is allocated. There is no need to re-initialize the tasklet each
time the channel is requested.

- Lars

Re: [PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

[Anand Moon]

hi Lars-Peter,

On 19 February 2016 at 13:45, Lars-Peter Clausen <lars@metafoo.de> wrote:
> On 02/19/2016 09:10 AM, Anand Moon wrote:
>> Hi Krzysztof,
>>
>> On 19 February 2016 at 12:50, Krzysztof Kozlowski
>> <k.kozlowski@samsung.com> wrote:
>>> On 19.02.2016 15:39, Anand Moon wrote:
>>>> Hi Krzysztof,
>>>>
>>>> On 19 February 2016 at 11:36, Krzysztof Kozlowski
>>>> <k.kozlowski@samsung.com> wrote:
>>>>> 2016-02-19 2:21 GMT+09:00 Anand Moon <linux.amoon@gmail.com>:
>>>>>> From: Anand Moon <linux.amoon@gmail.com>
>>>>>>
>>>>>> pl330_tasklet tasklet uses the same spinlock pch->lock for safe IRQ locking.
>>>>>> It's safe to initialize pl330_tasklet tasklet after release of the locking.
>>>>>
>>>>> This is tasklet init, not tasklet execution (which you are referring
>>>>> to in first sentence). I don't get how usage of spinlock during
>>>>> execution guarantees the safeness during init... Please describe why
>>>>> this is safe.
>>>>>
>>>>> Best regards,
>>>>> Krzysztof
>>>>>
>>>>
>>>> http://lxr.free-electrons.com/source/drivers/dma/pl330.c#L1972
>>>>
>>>> pl330_tasklet function which is initiated by tasklet_init is trying to lock
>>>> using same spin_unlock_irqsave/restore pch->lock.
>>>
>>> tasklet_init does not call pl330_tasklet (if this is what you mean by
>>> "initiated"). What is the correlation? Why are you referring to the
>>> locks in pl330_tasklet?
>>>
>>>> So better release the pch->lock and then initialize  the tasklet_init.
>>>
>>> Why "better"?
>>>
>>> Best regards,
>>> Krzysztof
>>>
>>
>> On SMP arch, tasklet_init could spawn the pl330_tasklet routine,
>> it could be any CPU which could take up this task.
>> So just for good timing of Initialization of the pl330_tasklet after
>> spin_unlock_irqrestore.
>> That is what I can figure out.
>
> Hi,
>
> tasklet_init() does not spwan the tasklet function, tasklet_schedule() does
> that.
>
> But there is still room for optimization here. If you want to move the
> tasklet_init() call please move it into pl330_probe() next to where the
> channel is allocated. There is no need to re-initialize the tasklet each
> time the channel is requested.
>
> - Lars
>

Thanks for clearing my miss-concept.

Best Regards.
-Anand moon

Re: [PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

[Anand Moon]

Hi Krzysztof,

On 19 February 2016 at 13:45, Lars-Peter Clausen <lars@metafoo.de> wrote:
> On 02/19/2016 09:10 AM, Anand Moon wrote:
>> Hi Krzysztof,
>>
>> On 19 February 2016 at 12:50, Krzysztof Kozlowski
>> <k.kozlowski@samsung.com> wrote:
>>> On 19.02.2016 15:39, Anand Moon wrote:
>>>> Hi Krzysztof,
>>>>
>>>> On 19 February 2016 at 11:36, Krzysztof Kozlowski
>>>> <k.kozlowski@samsung.com> wrote:
>>>>> 2016-02-19 2:21 GMT+09:00 Anand Moon <linux.amoon@gmail.com>:
>>>>>> From: Anand Moon <linux.amoon@gmail.com>
>>>>>>
>>>>>> pl330_tasklet tasklet uses the same spinlock pch->lock for safe IRQ locking.
>>>>>> It's safe to initialize pl330_tasklet tasklet after release of the locking.
>>>>>
>>>>> This is tasklet init, not tasklet execution (which you are referring
>>>>> to in first sentence). I don't get how usage of spinlock during
>>>>> execution guarantees the safeness during init... Please describe why
>>>>> this is safe.
>>>>>
>>>>> Best regards,
>>>>> Krzysztof
>>>>>
>>>>
>>>> http://lxr.free-electrons.com/source/drivers/dma/pl330.c#L1972
>>>>
>>>> pl330_tasklet function which is initiated by tasklet_init is trying to lock
>>>> using same spin_unlock_irqsave/restore pch->lock.
>>>
>>> tasklet_init does not call pl330_tasklet (if this is what you mean by
>>> "initiated"). What is the correlation? Why are you referring to the
>>> locks in pl330_tasklet?
>>>
>>>> So better release the pch->lock and then initialize  the tasklet_init.
>>>
>>> Why "better"?
>>>
>>> Best regards,
>>> Krzysztof
>>>
>>
>> On SMP arch, tasklet_init could spawn the pl330_tasklet routine,
>> it could be any CPU which could take up this task.
>> So just for good timing of Initialization of the pl330_tasklet after
>> spin_unlock_irqrestore.
>> That is what I can figure out.
>
> Hi,
>
> tasklet_init() does not spwan the tasklet function, tasklet_schedule() does
> that.
>
> But there is still room for optimization here. If you want to move the
> tasklet_init() call please move it into pl330_probe() next to where the
> channel is allocated. There is no need to re-initialize the tasklet each
> time the channel is requested.
>
> - Lars
>

After looking at the history of the change logs. I found below changes.

commit da331ba8e9c5de72a27e50f71105395bba6eebe0
Author: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Date:   Wed Jul 3 15:00:43 2013 -0700

    drivers/dma/pl330.c: fix locking in pl330_free_chan_resources()

    tasklet_kill() may sleep so call it before taking pch->lock.

---------------------------------------------
sorry for the noise.
Next time I will be more careful.

-Anand Moon