linux-kernel - Re: [Linaro-acpi] [PATCH] Mailbox: Complete wait event only if Tx was successful

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Date:	Fri, 12 Dec 2014 12:47:26 -0500
From:	Ashwin Chaugule <ashwin.chaugule@...aro.org>
To:	Sudeep Holla <sudeep.holla@....com>
Cc:	"jaswinder.singh@...aro.org" <jaswinder.singh@...aro.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"patches@...aro.org" <patches@...aro.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"broonie@...nel.org" <broonie@...nel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Linaro-acpi] [PATCH] Mailbox: Complete wait event only if Tx was successful

On 12 December 2014 at 03:43, Sudeep Holla <sudeep.holla@....com> wrote:
> Hi Ashwin,

Hi,

> On Thursday 11 December 2014 01:46 AM, Ashwin Chaugule wrote:
>>
>> If a wait_for_completion_timeout() call returns due to a timeout,
>> the mbox code can still call complete() after returning from the wait.
>> This can cause subsequent transmissions on a channel to fail, since
>> the wait_for_completion_timeout() sees the completion variable
>> is !=0, caused by the erroneous complete() call, and immediately
>> returns without waiting for the time as expected by the client.
>>
>> Fix this by calling complete() only if the TX was successful.
>>
>> Signed-off-by: Ashwin Chaugule <ashwin.chaugule@...aro.org>
>> ---
>>   drivers/mailbox/mailbox.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
>> index 17e9e4a..4acaddb 100644
>> --- a/drivers/mailbox/mailbox.c
>> +++ b/drivers/mailbox/mailbox.c
>> @@ -101,7 +101,7 @@ static void tx_tick(struct mbox_chan *chan, int r)
>>         if (mssg && chan->cl->tx_done)
>>                 chan->cl->tx_done(chan->cl, mssg, r);
>>
>> -       if (chan->cl->tx_block)
>> +       if ((!r) && chan->cl->tx_block)
>>                 complete(&chan->tx_complete);
>
>
> Just curious to check if there's another possible race which is
> a different issue.
>
> Suppose the timer fired and indicated that the Tx is complete, then
> it tries to execute complete while the wait_for_completion_timeout timed
> out. Does that make sense ?
>
> So if yes, how about adding !completion_done(..) to the check while you
> are at this ?

Yea. Seems like another race condition. I'll add it along with this..

Thanks,
Ashwin
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