From: javi.merino@arm•com (Javi Merino)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH v2] ARM: pl330: Fix a race condition
Date: Fri, 09 Dec 2011 14:52:23 +0000 [thread overview]
Message-ID: <4EE220A7.5070101@arm.com> (raw)
In-Reply-To: <CABb+yY0f8xxAj+rFeZ4e61Sfk0+0bMsAiZ-H5AeY4cfCd_VE5g@mail.gmail.com>
On 09/12/11 14:15, Jassi Brar wrote:
> On Fri, Dec 9, 2011 at 7:11 PM, Javi Merino <javi.merino@arm•com> wrote:
>> On 09/12/11 13:04, Jassi Brar wrote:
>>> Hi Javi,
>>>
>>> On 9 December 2011 17:28, Javi Merino <javi.merino@arm•com> wrote:
>>>>
>>>>>>>> Javi, could you please check if you too get the memcpy failure with
>>>>>>>> dmatest ?
>>>>>>>
>>>>> Ok, I think I've just reproduced it in my end with the kernel's dmatest
>>>>> module. After the first transaction it looks like the dma test wasn't
>>>>> able to issue any more transactions.
>>>>>
>>>> If you submit a transaction, it finishes and there's nothing else to run,
>>>> pl330_update() calls _start() but there is nothing to send. This is all
>>>> right. Then, if another transaction is submitted, pl330_submit_req() will
>>>> put it in buffer 0 again. This time, the PC of the DMA is in the last
>>>> instruction of buffer 0 (the DMAEND of the *previous* transaction that
>>>> finished long ago) so _thrd_active() thinks that this buffer is active,
>>>>
>>> Many thanks for the in-depth analysis.
>>>
>>> Though before the PC check, the IS_FREE() should return true since
>>> pl330_update() does MARK_FREE()
>>>
>>> Could you please check if the client's callback function called
>>> successfully for the
>>> first submitted transfer ?
>>
>> Yes, it calls MARK_FREE() and indeed in pl330_update(), _thrd_active()
>> returns 0. The problem comes when, afterwards, pl330_submit_req()
>> introduces a new request and chooses the same buffer. Then, IS_FREE()
>> returns false (obviously) but the PC of the DMA is at the end of the
>> buffer, so _thrd_active() claims that it is active so pl330_chan_ctrl()
>> doesn't start it.
>>
> OK, I see what you mean.
> We need to be able to differentiate between 'programmed' state
> and 'running' state.
> So instead of employing _state() or another marker, we'd rather
> alternate between buff 0 & 1 as a workaround.
>
> That is, I am ok with your following fix.
>
> - idx = IS_FREE(&thrd->req[0]) ? 0 : 1;
> + idx = IS_FREE(&thrd->req[1 - thrd->lstenq]) ? 1 - thrd->lstenq
> : thrd->lstenq;
No, see my last comment in the previous email. I think this freezes the
DMA in the following scenario:
pl330_submit_req()
pl330_chan_ctrl(PL33O_OP_START)
... wait for the transfer to finish ...
pl330_update()
...
pl330_submit_req()
pl330_submit_req()
pl330_chan_ctrl(PL330_OP_START)
The pl330 won't start because of the same reason, we have a request in
buffer 0 and _thrd_active() would say that it is active. This can
happen if drivers/dma/pl330.c:fill_queues() introduces two requests
before calling pl330_chan_ctrl(), which I'm not entirely sure that it
can't happen.
I think the best solution would be to revert
ee3f615819404a9438b2dd01b7a39f276d2737f2 and go back to my original
patch (in the beginning of this thread):
http://article.gmane.org/gmane.linux.ports.arm.kernel/133110
What do you think? Thanks,
Javi
next prev parent reply other threads:[~2011-12-09 14:52 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-19 17:11 [PATCH] ARM: pl330: Fix a race condition Javi Merino
2011-09-19 18:07 ` Jassi Brar
2011-09-20 13:36 ` Javi Merino
2011-10-05 12:57 ` Javi Merino
2011-10-06 9:10 ` [PATCH v2] " Javi Merino
2011-11-05 19:05 ` Thomas Abraham
2011-11-07 10:48 ` Javi Merino
2011-11-07 11:03 ` Thomas Abraham
2011-11-28 8:23 ` Boojin Kim
2011-11-28 16:36 ` Javi Merino
2011-11-29 3:41 ` Boojin Kim
2011-11-29 9:53 ` Javi Merino
2011-11-29 10:37 ` Jassi Brar
2011-12-07 7:52 ` Kukjin Kim
2011-12-07 10:01 ` Javi Merino
2011-12-07 20:54 ` Javi Merino
2011-12-09 11:58 ` Javi Merino
2011-12-09 13:04 ` Jassi Brar
2011-12-09 13:41 ` Javi Merino
2011-12-09 14:15 ` Jassi Brar
2011-12-09 14:52 ` Javi Merino [this message]
2011-12-09 16:50 ` Jassi Brar
2011-12-09 19:50 ` Javi Merino
2011-12-11 10:51 ` Jassi Brar
2011-12-11 15:09 ` Javi Merino
2011-12-11 17:10 ` Jassi Brar
2011-12-11 17:42 ` Javi Merino
2011-12-11 19:27 ` [PATCH] ARM: PL330: Fix driver freeze Javi Merino
2011-12-15 17:48 ` Javi Merino
2011-12-16 9:01 ` Tushar Behera
2011-12-16 6:27 ` Jassi Brar
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