linux-kernel - Re: [PATCH] mmc: atmel-mci: fix deadlock

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Date:	Tue, 15 May 2012 18:05:25 +0200
From:	Steffen Kühn <sk@...onit.com>
To:	"ludovic.desroches" <ludovic.desroches@...el.com>
CC:	Chris Ball <cjb@...top.org>, linux-mmc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Nicolas Ferre <nicolas.ferre@...el.com>
Subject: Re: [PATCH] mmc: atmel-mci: fix deadlock

Dear Ludovic,

in the meantime I have some new informations about the atmel-mci
deadlock problem: When you write permanently with

dd if=/dev/zero of=/dev/<device> bs=512

and removing the card you will get almost always a hang up. With
"printk" I have find out that the function "atmci_tasklet_func" doesn't
run anymore in this case.

I would ask you to add card inserting and removing during write and read
in your test cases.

Regards
Steffen


Am 09.05.2012 12:45, schrieb ludovic.desroches:
> Hi Steffen,
> 
> Le 05/09/2012 11:23 AM, Steffen Kühn a écrit :
>> solves a deadlock problem which appears when a mmc card is
>> removing and a process is reading from the card at the same time.
>> ---
>>   drivers/mmc/host/atmel-mci.c |    4 +++-
>>   1 files changed, 3 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/mmc/host/atmel-mci.c b/drivers/mmc/host/atmel-mci.c
>> index e94476b..effdc36 100644
>> --- a/drivers/mmc/host/atmel-mci.c
>> +++ b/drivers/mmc/host/atmel-mci.c
>> @@ -1499,8 +1499,10 @@ static void atmci_tasklet_func(unsigned long priv)
>> 			}
>>
>> 			if (!atmci_test_and_clear_pending(host,
>> -						EVENT_XFER_COMPLETE))
>> +						EVENT_XFER_COMPLETE)) {
>> +				host->stop_transfer(host);
>> 				break;
>> +            }
>>
>> 			atmci_set_completed(host, EVENT_XFER_COMPLETE);
>> 			prev_state = state = STATE_DATA_BUSY;
>> --
>> 1.7.2.5
> 
> Even if it solves your issue, I am not sure about the consequences of
> this fix even if it is working well in your case and with your hardware.
> 
> This condition allows to wait for the end of a transfer. The
> EVENT_XFER_COMPLETE flag is set when the dma transfer is complete (or pdc).
> If the transfer is not complete you will ask to stop it. I understand it
> could solve your issue but I am afraid it can also stop a transfer
> before its normal completion.
> 
> I am currently working on atmel-mci and the state machine would be
> changed.  So I prefer to wait the new atmel-mci version to take this
> patch. I will add your issue to my test cases.
> 
> 
> By the way, can you give me more details about your issue because I
> can't reproduce it on my side. If I remove the card while a process is
> reading from it, I also have I/O errors but I have no issue to detect a
> new card insertion.
> 
> 
> Regards
> 
> Ludovic

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