I want to sleep while holding a mutex

[Chan Kim]

> Yes that's correct. However I would recommend you look into how long the
> DMA bursts are before moving to a mutex. In addition softirqs are not
> internally locked and need to be implemented by the user for your
> information.
> Hope this Helps,
> Nick

Ok, thanks, I know the DMA burst can be quite long so I'll try sticking to mutex. 
I checked softirq and tasklet are in interrupt context, so I'll move the FIFO read stuff to workqueue.
Best regards,
Chan



보낸 사람 : "nick" <xerofoify at gmail.com>
보낸 날짜 : 2015-06-05 22:04:21 ( +09:00 )
받는 사람 : 김찬 <ckim at etri.re.kr>, kernelnewbies at kernelnewbies.org <kernelnewbies at kernelnewbies.org>
참조 : 
제목 : Re: I want to sleep while holding a mutex



On 2015-06-05 09:01 AM, Chan Kim wrote:
> 
>> While here is your issue your trying to sleep in an atomic/ non sleep able
>> context of your driver.
>> My best guess is in interrupt context but it could be somewhere else related
>> to your hardware.
>> Nick
> 
> For your information, I'm using smsc911x driver in linux ver 3.3.
> The FIFO burst write function is called inside ndo->start_xmit function (net device operation, I think it's process context)
> and FIFO burst read function is called from NAPI poll function. (it's in softirq context, is this a problem?).
> I remember somewhere reading the softirq is like interrupt context except the difference that interrupt is enabled during softirq processing.
> If softirq is where you should not sleep (in my case for DMA), then, I'll have to move it to workqueue or tasklet.
> Do you think my understanding sounds more like it?
> Chan
> 
Yes that's correct. However I would recommend you look into how long the DMA bursts are before moving to
a mutex. In addition softirqs are not internally locked and need to be implemented by the user for your
information.
Hope this Helps,
Nick 
> 
> 
> 보낸 사람 : "nick" 
> 보낸 날짜 : 2015-06-05 21:48:18 ( +09:00 )
> 받는 사람 : 김찬 , kernelnewbies at kernelnewbies.org 
> 참조 : 
> 제목 : Re: I want to sleep while holding a mutex
> 
> 
> 
> On 2015-06-05 08:45 AM, Chan Kim wrote:
>>
>>>>> Are you trying to use the mutex during a interrupt handler as you
>>>>> can't you need something atomic or not able to sleep like a spinlock.
>>>>> Nick
>>>>
>>>> I use mutex during FIFO burst write or burst read. I don't want other
>>> processes to mess up the FIFO access.
>>>> spinlock is not for long interval I understand.
>>>> Chan
>>>>
>>> That's during interrupt context. What you need to do is offload the data into
>>> main memory during interrupt context and lock with a spinlock. Afterwards
>>> you can use a mutex around the main work function called after the interrupt.
>>> Nick
>>
>>
>> I believe I lock_mutex and unlock_mutex are called in the process context. Both for transmission and for reception (rx is from softirq, it's ok.). It's only that the process is woken up by the interrupt routine. (ISR calls wake_up_interruptible). ISR doesn't lock or unlock any mutex.
>>
>> Chan
>>
> While here is your issue your trying to sleep in an atomic/ non sleep able context of your driver.
> My best guess is in interrupt context but it could be somewhere else related to your hardware.
> Nick
>>
>>
>> 보낸 사람 : "nick" 
>> 보낸 날짜 : 2015-06-05 21:40:20 ( +09:00 )
>> 받는 사람 : 김찬 , kernelnewbies at kernelnewbies.org 
>> 참조 : 
>> 제목 : Re: I want to sleep while holding a mutex
>>
>>
>>
>> On 2015-06-05 08:37 AM, 김찬 wrote:
>>>
>>>> Are you trying to use the mutex during a interrupt handler as you can't you
>>>> need something atomic or not able to sleep like a spinlock.
>>>> Nick
>>>
>>> I use mutex during FIFO burst write or burst read. I don't want other processes to mess up the FIFO access.
>>> spinlock is not for long interval I understand.
>>> Chan
>>>
>> That's during interrupt context. What you need to do is offload the data into main memory during interrupt
>> context and lock with a spinlock. Afterwards you can use a mutex around the main work function called 
>> after the interrupt.
>> Nick
>>> ________________________________
>>> 보낸 사람 : "nick" 
>>> 보낸 날짜 : 2015-06-05 21:34:25 ( +09:00 )
>>> 받는 사람 : 김찬 , kernelnewbies at kernelnewbies.org 
>>> 참조 :
>>> 제목 : Re: I want to sleep while holding a mutex
>>>
>>>
>>>
>>> On 2015-06-05 08:30 AM, Chan Kim wrote:
>>>> Hello,
>>>> I need to write to and read from a Ethernet chip's FIFO and for that I want to use DMA controller. So I modified an existing driver and made the process to sleep using wait_event_interruptible after triggering DMA transfer and made it woken up by ISR using wake_up_interruptible. My problem is that the original driver was using spinlock to protect the FIFO access. But as all know, while holding spinlock, I should not sleep. So I tried replacing spinlock with mutex. (Because, I might sleep while acquiring the mutex, and after getting the mutex, I'll sleep again after DMA trigger. I get woken up by the ISR, and I'll release the mutex. No problem! I thought. ) But I still get this 'scheduling while atomic BUG'. The question is : I need to go to sleep until DMA completion while holding a lock (for FIFO read and write). Isn't it ok to sleep while holding a mutex?
>>>> Best regards,
>>>> Chan Kim
>>>> _______________________________________________
>>>> Kernelnewbies mailing list
>>>> Kernelnewbies at kernelnewbies.org
>>>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>>>>
>>> Are you trying to use the mutex during a interrupt handler as you can't you need something
>>> atomic or not able to sleep like a spinlock.
>>> Nick