Re: [PATCH v2 2/4] rpmsg: core: use generic driver_override infrastructure

[Mathieu Poirier]

On Wed, 3 Jun 2026 at 21:52, Runyu Xiao <runyu.xiao@xxxxxxxxxx> wrote:
>
> RPMSG still keeps driver_override in bus-private storage.
>
> That private pointer can be updated from the sysfs driver_override
> attribute, and also from rpmsg_register_device_override(). Both paths
> replace the pointer and can free the old value.
>
> However, driver_match_device() can call rpmsg_dev_match() from
> __driver_attach() without holding the device lock, and rpmsg_dev_match()
> still dereferences that private pointer directly.
>
> This leaves the match path racing with concurrent driver_override
> updates, with the usual risk of comparing against freed memory.
>
> Switch rpmsg to the driver-core driver_override infrastructure. This
> removes the private storage, uses device_match_driver_override() for the
> locked read in rpmsg_dev_match(), and converts
> rpmsg_register_device_override() to device_set_driver_override() so the
> in-kernel override path uses the same core-managed storage. With that
> storage now owned by struct device, drop the remaining rpmsg transport
> release-path frees of rpdev->driver_override as well.
>
> Link: https://lore.kernel.org/driver-core/DGRGTIRHA62X.3RY09D9SOK77P@xxxxxxxxxx/
> Fixes: 39e47767ec9b ("rpmsg: Add driver_override device attribute for rpmsg_device")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Runyu Xiao <runyu.xiao@xxxxxxxxxx>
> ---
> drivers/rpmsg/qcom_glink_native.c |  2 --
> drivers/rpmsg/rpmsg_core.c        | 41 ++++++--------------------------------
> drivers/rpmsg/virtio_rpmsg_bus.c  |  1 -
> include/linux/rpmsg.h             |  4 ----

For the bottom 3:

Reviewed-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>

>  4 files changed, 6 insertions(+), 42 deletions(-)
>
> diff --git a/drivers/rpmsg/rpmsg_core.c b/drivers/rpmsg/rpmsg_core.c
> index e7f7831d37f8..11d3007db5cd 100644
> --- a/drivers/rpmsg/rpmsg_core.c
> +++ b/drivers/rpmsg/rpmsg_core.c
> @@ -358,33 +358,6 @@ rpmsg_show_attr(src, src, "0x%x\n");
>  rpmsg_show_attr(dst, dst, "0x%x\n");
>  rpmsg_show_attr(announce, announce ? "true" : "false", "%s\n");
>
> -static ssize_t driver_override_store(struct device *dev,
> -                                    struct device_attribute *attr,
> -                                    const char *buf, size_t count)
> -{
> -       struct rpmsg_device *rpdev = to_rpmsg_device(dev);
> -       int ret;
> -
> -       ret = driver_set_override(dev, &rpdev->driver_override, buf, count);
> -       if (ret)
> -               return ret;
> -
> -       return count;
> -}
> -
> -static ssize_t driver_override_show(struct device *dev,
> -                                   struct device_attribute *attr, char *buf)
> -{
> -       struct rpmsg_device *rpdev = to_rpmsg_device(dev);
> -       ssize_t len;
> -
> -       device_lock(dev);
> -       len = sysfs_emit(buf, "%s\n", rpdev->driver_override);
> -       device_unlock(dev);
> -       return len;
> -}
> -static DEVICE_ATTR_RW(driver_override);
> -
>  static ssize_t modalias_show(struct device *dev,
>                              struct device_attribute *attr, char *buf)
>  {
> @@ -405,7 +378,6 @@ static struct attribute *rpmsg_dev_attrs[] = {
>         &dev_attr_dst.attr,
>         &dev_attr_src.attr,
>         &dev_attr_announce.attr,
> -       &dev_attr_driver_override.attr,
>         NULL,
>  };
>  ATTRIBUTE_GROUPS(rpmsg_dev);
> @@ -424,9 +396,11 @@ static int rpmsg_dev_match(struct device *dev, const struct device_driver *drv)
>         const struct rpmsg_driver *rpdrv = to_rpmsg_driver(drv);
>         const struct rpmsg_device_id *ids = rpdrv->id_table;
>         unsigned int i;
> +       int ret;
>
> -       if (rpdev->driver_override)
> -               return !strcmp(rpdev->driver_override, drv->name);
> +       ret = device_match_driver_override(dev, drv);
> +       if (ret >= 0)
> +               return ret;
>
>         if (ids)
>                 for (i = 0; ids[i].name[0]; i++)
> @@ -533,6 +507,7 @@ static void rpmsg_dev_remove(struct device *dev)
>
>  static const struct bus_type rpmsg_bus = {
>         .name           = "rpmsg",
> +       .driver_override = true,
>         .match          = rpmsg_dev_match,
>         .dev_groups     = rpmsg_dev_groups,
>         .uevent         = rpmsg_uevent,
> @@ -560,9 +535,7 @@ int rpmsg_register_device_override(struct rpmsg_device *rpdev,
>
>         device_initialize(dev);
>         if (driver_override) {
> -               ret = driver_set_override(dev, &rpdev->driver_override,
> -                                         driver_override,
> -                                         strlen(driver_override));
> +               ret = device_set_driver_override(dev, driver_override);
>                 if (ret) {
>                         dev_err(dev, "device_set_override failed: %d\n", ret);
>                         put_device(dev);
> @@ -573,8 +546,6 @@ int rpmsg_register_device_override(struct rpmsg_device *rpdev,
>         ret = device_add(dev);
>         if (ret) {
>                 dev_err(dev, "device_add failed: %d\n", ret);
> -               kfree(rpdev->driver_override);
> -               rpdev->driver_override = NULL;
>                 put_device(dev);
>         }
>
> diff --git a/drivers/rpmsg/qcom_glink_native.c b/drivers/rpmsg/qcom_glink_native.c
> index 401a4ece0c97..d9d4468e4cbd 100644
> --- a/drivers/rpmsg/qcom_glink_native.c
> +++ b/drivers/rpmsg/qcom_glink_native.c
> @@ -1626,7 +1626,6 @@ static void qcom_glink_rpdev_release(struct device *dev)
>  {
>         struct rpmsg_device *rpdev = to_rpmsg_device(dev);
>
> -       kfree(rpdev->driver_override);
>         kfree(rpdev);
>  }
>
> @@ -1862,7 +1861,6 @@ static void qcom_glink_device_release(struct device *dev)
>
>         /* Release qcom_glink_alloc_channel() reference */
>         kref_put(&channel->refcount, qcom_glink_channel_release);
> -       kfree(rpdev->driver_override);
>         kfree(rpdev);
>  }
>
> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c b/drivers/rpmsg/virtio_rpmsg_bus.c
> index 5ae15111fb4f..1b8bb05924af 100644
> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> @@ -374,7 +374,6 @@ static void virtio_rpmsg_release_device(struct device *dev)
>         struct rpmsg_device *rpdev = to_rpmsg_device(dev);
>         struct virtio_rpmsg_channel *vch = to_virtio_rpmsg_channel(rpdev);
>
> -       kfree(rpdev->driver_override);
>         kfree(vch);
>  }
>
> diff --git a/include/linux/rpmsg.h b/include/linux/rpmsg.h
> index 83266ce14642..2e40eb54155e 100644
> --- a/include/linux/rpmsg.h
> +++ b/include/linux/rpmsg.h
> @@ -41,9 +41,6 @@ struct rpmsg_channel_info {
>   * rpmsg_device - device that belong to the rpmsg bus
>   * @dev: the device struct
>   * @id: device id (used to match between rpmsg drivers and devices)
> - * @driver_override: driver name to force a match; do not set directly,
> - *                   because core frees it; use driver_set_override() to
> - *                   set or clear it.
>   * @src: local address
>   * @dst: destination address
>   * @ept: the rpmsg endpoint of this channel
> @@ -53,7 +50,6 @@ struct rpmsg_channel_info {
>  struct rpmsg_device {
>         struct device dev;
>         struct rpmsg_device_id id;
> -       const char *driver_override;
>         u32 src;
>         u32 dst;
>         struct rpmsg_endpoint *ept;
> --
> 2.34.1