Re: [PATCH 2/2] iio: iio-mux: kzalloc instead of devm_kzalloc to ensure page alignment

Jonathan Cameron
2024-12-08T18:15:38Z

On Mon, 02 Dec 2024 16:11:08 +0100
Matteo Martelli <matteomartelli3@gmail.com> wrote:

> During channel configuration, the iio-mux driver allocates a page with
> devm_kzalloc(PAGE_SIZE) to read channel ext_info. However, the resulting
> buffer points to an offset of the page due to the devres header sitting
> at the beginning of the allocated area. This leads to failure in the
> provider driver when sysfs_emit* helpers are used to format the ext_info
> attributes.
>
> Switch to plain kzalloc version. The devres version is not strictly
> necessary as the buffer is only accessed during the channel
> configuration phase. Rely on __free cleanup to deallocate the buffer.
> Also, move the ext_info handling into a new function to have the page
> buffer definition and assignment in one statement as suggested by
> cleanup documentation.
>
> Signed-off-by: Matteo Martelli <matteomartelli3@gmail.com>
This seems fine to me, but the diff ended up a bit complex, so I'd like
Peter to take a look as well before I apply it.

Do you have a board that is hitting this? If so, a fixes tag is definitely
appropriate. I think it is probably appropriate even it not.

Jonathan

> ---
> drivers/iio/multiplexer/iio-mux.c | 84 +++++++++++++++++++++------------------
> 1 file changed, 46 insertions(+), 38 deletions(-)
>
> diff --git a/drivers/iio/multiplexer/iio-mux.c b/drivers/iio/multiplexer/iio-mux.c
> index 2953403bef53bbe47a97a8ab1c475ed88d7f86d2..c309d991490c63ba4299f1cda7102f10dcf54982 100644
> --- a/drivers/iio/multiplexer/iio-mux.c
> +++ b/drivers/iio/multiplexer/iio-mux.c
> @@ -7,6 +7,7 @@
> * Author: Peter Rosin <peda@axentia.se>
> */
>
> +#include <linux/cleanup.h>
> #include <linux/err.h>
> #include <linux/iio/consumer.h>
> #include <linux/iio/iio.h>
> @@ -237,49 +238,18 @@ static ssize_t mux_write_ext_info(struct iio_dev *indio_dev, uintptr_t private,
> return ret;
> }
>
> -static int mux_configure_channel(struct device *dev, struct mux *mux,
> - u32 state, const char *label, int idx)
> +static int mux_configure_chan_ext_info(struct device *dev, struct mux *mux,
> + int idx, int num_ext_info)
> {
> struct mux_child *child = &mux->child[idx];
> - struct iio_chan_spec *chan = &mux->chan[idx];
> struct iio_chan_spec const *pchan = mux->parent->channel;
> - char *page = NULL;
> - int num_ext_info;
> int i;
> int ret;
>
> - chan->indexed = 1;
> - chan->output = pchan->output;
> - chan->datasheet_name = label;
> - chan->ext_info = mux->ext_info;
> -
> - ret = iio_get_channel_type(mux->parent, &chan->type);
> - if (ret < 0) {
> - dev_err(dev, "failed to get parent channel type\n");
> - return ret;
> - }
> -
> - if (iio_channel_has_info(pchan, IIO_CHAN_INFO_RAW))
> - chan->info_mask_separate |= BIT(IIO_CHAN_INFO_RAW);
> - if (iio_channel_has_info(pchan, IIO_CHAN_INFO_SCALE))
> - chan->info_mask_separate |= BIT(IIO_CHAN_INFO_SCALE);
> -
> - if (iio_channel_has_available(pchan, IIO_CHAN_INFO_RAW))
> - chan->info_mask_separate_available |= BIT(IIO_CHAN_INFO_RAW);
> -
> - if (state >= mux_control_states(mux->control)) {
> - dev_err(dev, "too many channels\n");
> - return -EINVAL;
> - }
> -
> - chan->channel = state;
> + char *page __free(kfree) = kzalloc(PAGE_SIZE, GFP_KERNEL);
> + if (!page)
> + return -ENOMEM;
>
> - num_ext_info = iio_get_channel_ext_info_count(mux->parent);
> - if (num_ext_info) {
> - page = devm_kzalloc(dev, PAGE_SIZE, GFP_KERNEL);
> - if (!page)
> - return -ENOMEM;
> - }
> child->ext_info_cache = devm_kcalloc(dev,
> num_ext_info,
> sizeof(*child->ext_info_cache),
> @@ -318,8 +288,46 @@ static int mux_configure_channel(struct device *dev, struct mux *mux,
> child->ext_info_cache[i].size = ret;
> }
>
> - if (page)
> - devm_kfree(dev, page);
> + return 0;
> +}
> +
> +static int mux_configure_channel(struct device *dev, struct mux *mux, u32 state,
> + const char *label, int idx)
> +{
> + struct iio_chan_spec *chan = &mux->chan[idx];
> + struct iio_chan_spec const *pchan = mux->parent->channel;
> + int num_ext_info;
> + int ret;
> +
> + chan->indexed = 1;
> + chan->output = pchan->output;
> + chan->datasheet_name = label;
> + chan->ext_info = mux->ext_info;
> +
> + ret = iio_get_channel_type(mux->parent, &chan->type);
> + if (ret < 0) {
> + dev_err(dev, "failed to get parent channel type\n");
> + return ret;
> + }
> +
> + if (iio_channel_has_info(pchan, IIO_CHAN_INFO_RAW))
> + chan->info_mask_separate |= BIT(IIO_CHAN_INFO_RAW);
> + if (iio_channel_has_info(pchan, IIO_CHAN_INFO_SCALE))
> + chan->info_mask_separate |= BIT(IIO_CHAN_INFO_SCALE);
> +
> + if (iio_channel_has_available(pchan, IIO_CHAN_INFO_RAW))
> + chan->info_mask_separate_available |= BIT(IIO_CHAN_INFO_RAW);
> +
> + if (state >= mux_control_states(mux->control)) {
> + dev_err(dev, "too many channels\n");
> + return -EINVAL;
> + }
> +
> + chan->channel = state;
> +
> + num_ext_info = iio_get_channel_ext_info_count(mux->parent);
> + if (num_ext_info)
> + return mux_configure_chan_ext_info(dev, mux, idx, num_ext_info);
>
> return 0;
> }
>