linux-kernel - Re: [PATCH] 3.19-rc4: Fix race condition in i.MX serial port driver

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Message-ID: <trinity-9d19a383-9282-48e7-bcaf-2da48e937031-1422713009062@3capp-gmx-bs71>
Date:	Sat, 31 Jan 2015 15:03:29 +0100
From:	"Michael Doswald" <michael.doswald@....net>
To:	"Greg KH" <greg@...ah.com>
Cc:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] 3.19-rc4: Fix race condition in i.MX serial port driver

On 31.01.2015 00:25, Greg KH wrote:
>> Under pressure, the imx.c device driver may transfer the same data multiple
>> times. 
>>
>> Reason: 
>> Function imx_dma_tx checks for an active DMA transfer by calling
>> dmaengine_tx_status. The return value may indicate that no transfer is 
>> running while the dma_tx_callback function is still being executed. In 
>> this case the xmit->tail pointer may not be updated to the correct value 
>> when imx_dma_tx initiates a new DMA transfer, which will result in a DMA
>> transfer with the same base address as the previous one.
>>
>> Patch:
>> Use existing dma_is_txing variable to guard DMA transfer initiation instead
>> of dmaengine_tx_status. Clear dma_is_txing at the end of the DMA callback
>> function therefore extending the critical section where the port lock is
>> held. Critical section extension is in line with the callback function 
>> of other drivers, e.g. serial-tegra.c (tegra_uart_tx_dma_complete).
>>  
>>  
>> Signed-off-by: Michael Doswald <michael.doswald@....net>
>> ---
>>  drivers/tty/serial/imx.c | 11 ++++-------
>>  1 file changed, 4 insertions(+), 7 deletions(-)
>
> Fails to apply to my tree :(
>

Hi,

I'm sorry, it seems I made the mistake to create the patch against 3.19-rc3 instead of rc4. I just saw that the rc4 tree already contains a patch which fixes the exact same problem (commit 42f752b3fbcfee9c27e4f6f6216e60e130ba98c8 by Dirk Behme).

Thank you for notifying me.

Regards,
Michael
 
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