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

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Date:	Fri, 30 Jan 2015 15:25:09 -0800
From:	Greg KH <greg@...ah.com>
To:	Michael Doswald <michael.doswald@....net>
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 Tue, Jan 13, 2015 at 05:07:08PM +0100, Michael Doswald 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 :(

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