Re: [PATCH 2/4] firmware_loader: Move module refcounts to allow unloading

From: Russ Weight
Date: Thu Oct 31 2024 - 11:56:24 EST


On Tue, Oct 29, 2024 at 06:39:02PM +0000, Dionna Glaze wrote:
> If a kernel module registers a firmware upload API ops set, then it's
> unable to be moved due to effectively a cyclic reference that the module
> depends on the upload which depends on the module.
>
> Instead, only require the try_module_get when an upload is requested to
> disallow unloading a module only while the upload is in progress.
>
> Fixes: 97730bbb242cd ("firmware_loader: Add firmware-upload support")
>
> CC: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> CC: Russ Weight <russ.weight@xxxxxxxxx>
> CC: Danilo Krummrich <dakr@xxxxxxxxxx>
> CC: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> CC: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
> CC: Tianfei zhang <tianfei.zhang@xxxxxxxxx>
>
> Signed-off-by: Dionna Glaze <dionnaglaze@xxxxxxxxxx>
> Change-Id: Ifac9513de2f58a5120d4c0a681e969cd71cd3c68
> ---
> drivers/base/firmware_loader/sysfs_upload.c | 28 ++++++++++++++-------
> 1 file changed, 19 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/base/firmware_loader/sysfs_upload.c b/drivers/base/firmware_loader/sysfs_upload.c
> index 829270067d163..97b0ae855b5f0 100644
> --- a/drivers/base/firmware_loader/sysfs_upload.c
> +++ b/drivers/base/firmware_loader/sysfs_upload.c
> @@ -103,6 +103,10 @@ static ssize_t cancel_store(struct device *dev, struct device_attribute *attr,
> if (fwlp->progress == FW_UPLOAD_PROG_IDLE)
> ret = -ENODEV;
>
> + /*
> + * Not idle, so fw_upload_start already called try_module_get.
> + * No need to get/put around cancel.
> + */

I'm not sure why you think this comment is needed. I think it can
be removed


> fwlp->ops->cancel(fwlp->fw_upload);
> mutex_unlock(&fwlp->lock);
>
> @@ -164,11 +168,13 @@ static void fw_upload_main(struct work_struct *work)
> enum fw_upload_err ret;
> struct device *fw_dev;
> struct fw_upload *fwl;
> + struct module *module;

No need for a local variable here - module is only accessed once,
so just reference it as fwlp->module.

>
> fwlp = container_of(work, struct fw_upload_priv, work);
> fwl = fwlp->fw_upload;
> fw_sysfs = (struct fw_sysfs *)fwl->priv;
> fw_dev = &fw_sysfs->dev;
> + module = fwlp->module;
>
> fw_upload_update_progress(fwlp, FW_UPLOAD_PROG_PREPARING);
> ret = fwlp->ops->prepare(fwl, fwlp->data, fwlp->remaining_size);
> @@ -204,6 +210,7 @@ static void fw_upload_main(struct work_struct *work)
> fwlp->ops->cleanup(fwl);
>
> putdev_exit:
> + module_put(module);
> put_device(fw_dev->parent);
>
> /*
> @@ -238,7 +245,11 @@ int fw_upload_start(struct fw_sysfs *fw_sysfs)
> return 0;
> }
>
> +
Remove the extra blank line above.

> fwlp = fw_sysfs->fw_upload_priv;
> + if (!try_module_get(fwlp->module)) /* released in fw_upload_main */
> + return -EFAULT;
> +
> mutex_lock(&fwlp->lock);
>
> /* Do not interfere with an on-going fw_upload */
> @@ -310,13 +321,10 @@ firmware_upload_register(struct module *module, struct device *parent,
> return ERR_PTR(-EINVAL);
> }
>
> - if (!try_module_get(module))
> - return ERR_PTR(-EFAULT);
> -
> fw_upload = kzalloc(sizeof(*fw_upload), GFP_KERNEL);
> if (!fw_upload) {
> ret = -ENOMEM;
> - goto exit_module_put;
> + goto exit_err;
> }
>
> fw_upload_priv = kzalloc(sizeof(*fw_upload_priv), GFP_KERNEL);
> @@ -358,7 +366,7 @@ firmware_upload_register(struct module *module, struct device *parent,
> if (ret) {
> dev_err(fw_dev, "%s: device_register failed\n", __func__);
> put_device(fw_dev);
> - goto exit_module_put;
> + goto exit_err;
> }
>
> return fw_upload;
> @@ -372,8 +380,7 @@ firmware_upload_register(struct module *module, struct device *parent,
> free_fw_upload:
> kfree(fw_upload);
>
> -exit_module_put:
> - module_put(module);
> +exit_err:
>
> return ERR_PTR(ret);
> }
> @@ -387,7 +394,6 @@ void firmware_upload_unregister(struct fw_upload *fw_upload)
> {
> struct fw_sysfs *fw_sysfs = fw_upload->priv;
> struct fw_upload_priv *fw_upload_priv = fw_sysfs->fw_upload_priv;
> - struct module *module = fw_upload_priv->module;
>
> mutex_lock(&fw_upload_priv->lock);
> if (fw_upload_priv->progress == FW_UPLOAD_PROG_IDLE) {
> @@ -395,6 +401,11 @@ void firmware_upload_unregister(struct fw_upload *fw_upload)
> goto unregister;
> }
>
> + /*
> + * No need to try_module_get/module_put around the op since only the
> + * module itself will call unregister, usually when the refcount has
> + * dropped to zero and it's cleaning up dependencies to destroy itself.
> + */

This comment is not needed.

Thanks,
- Russ

> fw_upload_priv->ops->cancel(fw_upload);
> mutex_unlock(&fw_upload_priv->lock);
>
> @@ -403,6 +414,5 @@ void firmware_upload_unregister(struct fw_upload *fw_upload)
>
> unregister:
> device_unregister(&fw_sysfs->dev);
> - module_put(module);
> }
> EXPORT_SYMBOL_GPL(firmware_upload_unregister);
> --
> 2.47.0.163.g1226f6d8fa-goog
>