Re: [PATCH] mfd: viperboard: allocate I/O buffer separately

Johan Hovold
2014-09-22T16:11:45Z

On Mon, Sep 22, 2014 at 05:46:52PM +0300, Octavian Purdila wrote:
> Currently the I/O buffer is allocated part of the device status
> structure, potentially sharing the same cache line with other members
> in this structure.
>
> Allocate the buffer separately, to avoid the I/O operations corrupting
> the device status structure due to cache line sharing.
>
> Compiled tested only, as I don't have access to hardware.
>
> Signed-off-by: Octavian Purdila <octavian.purdila@intel.com>
> ---

Change itself looks sane, although the driver's use of a shared buffer
and relying on undocumented locking is a different story.

However, you do more than your commit message claims below.

> drivers/mfd/viperboard.c | 16 ++++++++++------
> include/linux/mfd/viperboard.h | 2 +-
> 2 files changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/mfd/viperboard.c b/drivers/mfd/viperboard.c
> index e00f534..d27c131 100644
> --- a/drivers/mfd/viperboard.c
> +++ b/drivers/mfd/viperboard.c
> @@ -59,9 +59,13 @@ static int vprbrd_probe(struct usb_interface *interface,
>
> /* allocate memory for our device state and initialize it */
> vb = kzalloc(sizeof(*vb), GFP_KERNEL);
> - if (vb == NULL) {
> - dev_err(&interface->dev, "Out of memory\n");

Here you're also removing a redundant OOM message.

> + if (vb == NULL)
> return -ENOMEM;
> +
> + vb->buf = kzalloc(sizeof(struct vprbrd_i2c_write_msg), GFP_KERNEL);
> + if (vb->buf == NULL) {
> + ret = -ENOMEM;
> + goto error;
> }
>
> mutex_init(&vb->lock);
> @@ -103,10 +107,9 @@ static int vprbrd_probe(struct usb_interface *interface,
> return 0;
>
> error:
> - if (vb) {

And cleaning up the error path.

> - usb_put_dev(vb->usb_dev);
> - kfree(vb);
> - }
> + usb_put_dev(vb->usb_dev);
> + kfree(vb->buf);
> + kfree(vb);
>
> return ret;
> }

Don't mix fixes and clean ups like this, but rather submit them as
separate patches.

Johan