linux-kernel - Re: [PATCH] dmaengine: pl330: initialize tasklet after spin_unlock

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Message-ID: <CANAwSgS2WOxirQOP3Yh7Y56yQVKrGU-4FopaK7PXupmgz5UrNQ@mail.gmail.com>
Date:	Fri, 19 Feb 2016 12:09:59 +0530
From:	Anand Moon <linux.amoon@...il.com>
To:	Krzysztof Kozlowski <k.kozlowski@...sung.com>
Cc:	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	dmaengine@...r.kernel.org,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dmaengine: pl330: initialize tasklet after spin_unlock_irqrestore

Hi Krzysztof,

On 19 February 2016 at 11:36, Krzysztof Kozlowski
<k.kozlowski@...sung.com> wrote:
> 2016-02-19 2:21 GMT+09:00 Anand Moon <linux.amoon@...il.com>:
>> From: Anand Moon <linux.amoon@...il.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@...il.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
>>
>> --
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