[PATCH V2] mxs/spi: Fix misuse of init_completion

[PATCH V2] mxs/spi: Fix misuse of init_completion

[Marek Vasut]

The init_completion() call does reinit not only the variable carrying
the flag that the completion finished, but also initialized the
waitqueue associated with the completion. On the contrary, the
INIT_WAITQUEUE() call only reinits the flag.

In case there was anything still stuck in the waitqueue, subsequent call
to init_completion() would be able to create possible race condition. This
patch uses the proper function and moves init_completion() into .probe() call
of the driver, to be issued only once.

Note that such scenario is impossible, since two threads can never enter the
mxs_spi_txrx_dma(), since whole this section is protected by mutex in SPI core.
This by no means allows this issue to exit though.

Signed-off-by: Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>
Cc: Chris Ball <cjb-2X9k7bc8m7Mdnm+yROfE0A@public.gmane.org>
Cc: Shawn Guo <shawn.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Cc: Mark Brown <broonie-yzvPICuk2AATkU/dhu1WVueM+bqZidxxQQ4Iyu8u01E@public.gmane.org>
Cc: Fabio Estevam <fabio.estevam-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
---
 drivers/spi/spi-mxs.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

V2: Update the patch description and snap a whip over myself for being lazy to
    write one in the first place!

diff --git a/drivers/spi/spi-mxs.c b/drivers/spi/spi-mxs.c
index 331f600..c965cc6 100644
--- a/drivers/spi/spi-mxs.c
+++ b/drivers/spi/spi-mxs.c
@@ -230,7 +230,7 @@ static int mxs_spi_txrx_dma(struct mxs_spi *spi, int cs,
 		return -EINVAL;
 	}
 
-	init_completion(&spi->c);
+	INIT_COMPLETION(spi->c);
 
 	if (*first)
 		pio |= BM_SSP_CTRL0_LOCK_CS;
@@ -560,6 +560,8 @@ static int __devinit mxs_spi_probe(struct platform_device *pdev)
 	ssp->devid = devid;
 	ssp->dma_channel = dma_channel;
 
+	init_completion(&spi->c);
+
 	ret = devm_request_irq(&pdev->dev, irq_err, mxs_ssp_irq_handler, 0,
 			       DRIVER_NAME, ssp);
 	if (ret)
-- 
1.7.10.4


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[PATCH V2] mxs/spi: Fix misuse of init_completion

[Marek Vasut]

The init_completion() call does reinit not only the variable carrying
the flag that the completion finished, but also initialized the
waitqueue associated with the completion. On the contrary, the
INIT_WAITQUEUE() call only reinits the flag.

In case there was anything still stuck in the waitqueue, subsequent call
to init_completion() would be able to create possible race condition. This
patch uses the proper function and moves init_completion() into .probe() call
of the driver, to be issued only once.

Note that such scenario is impossible, since two threads can never enter the
mxs_spi_txrx_dma(), since whole this section is protected by mutex in SPI core.
This by no means allows this issue to exit though.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chris Ball <cjb@laptop.org>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
---
 drivers/spi/spi-mxs.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

V2: Update the patch description and snap a whip over myself for being lazy to
    write one in the first place!

diff --git a/drivers/spi/spi-mxs.c b/drivers/spi/spi-mxs.c
index 331f600..c965cc6 100644
--- a/drivers/spi/spi-mxs.c
+++ b/drivers/spi/spi-mxs.c
@@ -230,7 +230,7 @@ static int mxs_spi_txrx_dma(struct mxs_spi *spi, int cs,
 		return -EINVAL;
 	}
 
-	init_completion(&spi->c);
+	INIT_COMPLETION(spi->c);
 
 	if (*first)
 		pio |= BM_SSP_CTRL0_LOCK_CS;
@@ -560,6 +560,8 @@ static int __devinit mxs_spi_probe(struct platform_device *pdev)
 	ssp->devid = devid;
 	ssp->dma_channel = dma_channel;
 
+	init_completion(&spi->c);
+
 	ret = devm_request_irq(&pdev->dev, irq_err, mxs_ssp_irq_handler, 0,
 			       DRIVER_NAME, ssp);
 	if (ret)
-- 
1.7.10.4

Re: [PATCH V2] mxs/spi: Fix misuse of init_completion

[Chris Ball]

Hi Marek,

On Thu, Aug 23 2012, Marek Vasut wrote:
> The init_completion() call does reinit not only the variable carrying
> the flag that the completion finished, but also initialized the
> waitqueue associated with the completion. On the contrary, the
> INIT_WAITQUEUE() call only reinits the flag.
>
> In case there was anything still stuck in the waitqueue, subsequent call
> to init_completion() would be able to create possible race condition. This
> patch uses the proper function and moves init_completion() into .probe() call
> of the driver, to be issued only once.
>
> Note that such scenario is impossible, since two threads can never enter the
> mxs_spi_txrx_dma(), since whole this section is protected by mutex in SPI core.
> This by no means allows this issue to exit though.
>
> Signed-off-by: Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>

Thanks for writing that up -- I appreciate seeing the explanation of the
problems this could have caused.

- Chris.
-- 
Chris Ball   <cjb-2X9k7bc8m7Mdnm+yROfE0A@public.gmane.org>   <http://printf.net/>
One Laptop Per Child

------------------------------------------------------------------------------
Live Security Virtual Conference
Exclusive live event will cover all the ways today's security and 
threat landscape has changed and how IT managers can respond. Discussions 
will include endpoint security, mobile security and the latest in malware 
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/

[PATCH V2] mxs/spi: Fix misuse of init_completion

[Chris Ball]

Hi Marek,

On Thu, Aug 23 2012, Marek Vasut wrote:
> The init_completion() call does reinit not only the variable carrying
> the flag that the completion finished, but also initialized the
> waitqueue associated with the completion. On the contrary, the
> INIT_WAITQUEUE() call only reinits the flag.
>
> In case there was anything still stuck in the waitqueue, subsequent call
> to init_completion() would be able to create possible race condition. This
> patch uses the proper function and moves init_completion() into .probe() call
> of the driver, to be issued only once.
>
> Note that such scenario is impossible, since two threads can never enter the
> mxs_spi_txrx_dma(), since whole this section is protected by mutex in SPI core.
> This by no means allows this issue to exit though.
>
> Signed-off-by: Marek Vasut <marex@denx.de>

Thanks for writing that up -- I appreciate seeing the explanation of the
problems this could have caused.

- Chris.
-- 
Chris Ball   <cjb@laptop.org>   <http://printf.net/>
One Laptop Per Child

Re: [PATCH V2] mxs/spi: Fix misuse of init_completion

[Marek Vasut]

Dear Chris Ball,

> Hi Marek,
> 
> On Thu, Aug 23 2012, Marek Vasut wrote:
> > The init_completion() call does reinit not only the variable carrying
> > the flag that the completion finished, but also initialized the
> > waitqueue associated with the completion. On the contrary, the
> > INIT_WAITQUEUE() call only reinits the flag.

Darn, it's INIT_COMPLETION() of course.

> > In case there was anything still stuck in the waitqueue, subsequent call
> > to init_completion() would be able to create possible race condition.
> > This patch uses the proper function and moves init_completion() into
> > .probe() call of the driver, to be issued only once.
> > 
> > Note that such scenario is impossible, since two threads can never enter
> > the mxs_spi_txrx_dma(), since whole this section is protected by mutex
> > in SPI core. This by no means allows this issue to exit though.
> > 
> > Signed-off-by: Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>
> 
> Thanks for writing that up -- I appreciate seeing the explanation of the
> problems this could have caused.

You're very welcome, I was really lazy, sorry about that and thanks for pushing 
me ;-) I hope someone might eventually even find this explanation useful.

> - Chris.

Best regards,
Marek Vasut

------------------------------------------------------------------------------
Live Security Virtual Conference
Exclusive live event will cover all the ways today's security and 
threat landscape has changed and how IT managers can respond. Discussions 
will include endpoint security, mobile security and the latest in malware 
threats. http://www.accelacomm.com/jaw/sfrnl04242012/114/50122263/

[PATCH V2] mxs/spi: Fix misuse of init_completion

[Marek Vasut]

Dear Chris Ball,

> Hi Marek,
> 
> On Thu, Aug 23 2012, Marek Vasut wrote:
> > The init_completion() call does reinit not only the variable carrying
> > the flag that the completion finished, but also initialized the
> > waitqueue associated with the completion. On the contrary, the
> > INIT_WAITQUEUE() call only reinits the flag.

Darn, it's INIT_COMPLETION() of course.

> > In case there was anything still stuck in the waitqueue, subsequent call
> > to init_completion() would be able to create possible race condition.
> > This patch uses the proper function and moves init_completion() into
> > .probe() call of the driver, to be issued only once.
> > 
> > Note that such scenario is impossible, since two threads can never enter
> > the mxs_spi_txrx_dma(), since whole this section is protected by mutex
> > in SPI core. This by no means allows this issue to exit though.
> > 
> > Signed-off-by: Marek Vasut <marex@denx.de>
> 
> Thanks for writing that up -- I appreciate seeing the explanation of the
> problems this could have caused.

You're very welcome, I was really lazy, sorry about that and thanks for pushing 
me ;-) I hope someone might eventually even find this explanation useful.

> - Chris.

Best regards,
Marek Vasut