[PATCH] i2c: mxs: Fix misuse init_completion

[PATCH] i2c: mxs: Fix misuse 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_COMPLETION() 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_i2c_xfer_msg(), since whole this section is protected by mutex in I2C core.
This by no means allows this issue to exit though.

Signed-off-by: Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>
Cc: Fabio Estevam <fabio.estevam-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
Cc: Shawn Guo <shawn.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
Cc: Wolfram Sang <w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
---
 drivers/i2c/busses/i2c-mxs.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/i2c/busses/i2c-mxs.c b/drivers/i2c/busses/i2c-mxs.c
index 6ed53da..47d5d53 100644
--- a/drivers/i2c/busses/i2c-mxs.c
+++ b/drivers/i2c/busses/i2c-mxs.c
@@ -316,7 +316,7 @@ static int mxs_i2c_xfer_msg(struct i2c_adapter *adap, struct i2c_msg *msg,
 	if (msg->len == 0)
 		return -EINVAL;
 
-	init_completion(&i2c->cmd_complete);
+	INIT_COMPLETION(i2c->cmd_complete);
 	i2c->cmd_err = 0;
 
 	ret = mxs_i2c_dma_setup_xfer(adap, msg, flags);
@@ -473,6 +473,8 @@ static int __devinit mxs_i2c_probe(struct platform_device *pdev)
 	i2c->dev = dev;
 	i2c->speed = &mxs_i2c_95kHz_config;
 
+	init_completion(&i2c->cmd_complete);
+
 	if (dev->of_node) {
 		err = mxs_i2c_get_ofdata(i2c);
 		if (err)
-- 
1.7.10.4

Re: [PATCH] i2c: mxs: Fix misuse init_completion

[Marek Vasut]

Hi,

> 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_COMPLETION() 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_i2c_xfer_msg(), since whole this section is protected by mutex in
> I2C core. This by no means allows this issue to exit though.
> 
> Signed-off-by: Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>
> Cc: Fabio Estevam <fabio.estevam-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> Cc: Shawn Guo <shawn.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> Cc: Wolfram Sang <w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>

Why is this not applied / not in stable please?

Also, what about the other MXS I2C patches?

Thanks!

Best regards,
Marek Vasut

Re: [PATCH] i2c: mxs: Fix misuse init_completion

[Wolfram Sang]

> > 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_COMPLETION() 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_i2c_xfer_msg(), since whole this section is protected by mutex in
> > I2C core. This by no means allows this issue to exit though.
> > 
> > Signed-off-by: Marek Vasut <marex-ynQEQJNshbs@public.gmane.org>
> > Cc: Fabio Estevam <fabio.estevam-KZfg59tc24xl57MIdRCFDg@public.gmane.org>
> > Cc: Shawn Guo <shawn.guo-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> > Cc: Wolfram Sang <w.sang-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
> 
> Why is this not applied / not in stable please?

Thanks, applied. It will go to 3.8 but not to stable, since it is not
really a bugfix as you also mentioned.

> Also, what about the other MXS I2C patches?

Pending, obviously. New next branch probably this weekend.

Thanks,

   Wolfram