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Message-ID: <ZZu7Uf3kC1i3zho3@yilunxu-OptiPlex-7050>
Date: Mon, 8 Jan 2024 17:07:29 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Marco Pagani <marpagan@...hat.com>
Cc: Moritz Fischer <mdf@...nel.org>, Wu Hao <hao.wu@...el.com>,
Xu Yilun <yilun.xu@...el.com>, Tom Rix <trix@...hat.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
linux-kernel@...r.kernel.org, linux-fpga@...r.kernel.org
Subject: Re: [RFC PATCH v4 1/1] fpga: add an owner and use it to take the
low-level module's refcount
On Sat, Jan 06, 2024 at 12:15:26AM +0100, Marco Pagani wrote:
> Add a module owner field to the fpga_manager struct to take the
> low-level control module refcount instead of assuming that the parent
> device has a driver and using its owner pointer. The owner is now
> passed as an additional argument at registration time. To this end,
> the functions for registration have been modified to take an additional
> owner parameter and renamed to avoid conflicts. The old function names
> are now used for helper macros that automatically set the module that
> registers the fpga manager as the owner. This ensures compatibility
> with existing low-level control modules and reduces the chances of
> registering a manager without setting the owner.
>
> To detect when the owner module pointer becomes stale, set the mops
> pointer to null during fpga_mgr_unregister() and test it before taking
> the module's refcount. Use a mutex to protect against a crash that can
> happen if __fpga_mgr_get() gets suspended between testing the mops
> pointer and taking the refcount while the low-level module is being
> unloaded.
>
> Other changes: opportunistically move put_device() from __fpga_mgr_get()
> to fpga_mgr_get() and of_fpga_mgr_get() to improve code clarity since
> the device refcount in taken in these functions.
>
> Fixes: 654ba4cc0f3e ("fpga manager: ensure lifetime with of_fpga_mgr_get")
> Suggested-by: Xu Yilun <yilun.xu@...el.com>
> Signed-off-by: Marco Pagani <marpagan@...hat.com>
> ---
> drivers/fpga/fpga-mgr.c | 93 ++++++++++++++++++++++-------------
> include/linux/fpga/fpga-mgr.h | 80 +++++++++++++++++++++++++++---
> 2 files changed, 134 insertions(+), 39 deletions(-)
>
> diff --git a/drivers/fpga/fpga-mgr.c b/drivers/fpga/fpga-mgr.c
> index 06651389c592..d7bfbdfdf2fc 100644
> --- a/drivers/fpga/fpga-mgr.c
> +++ b/drivers/fpga/fpga-mgr.c
> @@ -664,20 +664,20 @@ static struct attribute *fpga_mgr_attrs[] = {
> };
> ATTRIBUTE_GROUPS(fpga_mgr);
>
> -static struct fpga_manager *__fpga_mgr_get(struct device *dev)
> +static struct fpga_manager *__fpga_mgr_get(struct device *mgr_dev)
> {
> struct fpga_manager *mgr;
>
> - mgr = to_fpga_manager(dev);
> + mgr = to_fpga_manager(mgr_dev);
>
> - if (!try_module_get(dev->parent->driver->owner))
> - goto err_dev;
> + mutex_lock(&mgr->mops_mutex);
>
> - return mgr;
> + if (!mgr->mops || !try_module_get(mgr->mops_owner))
Why move the owner out of struct fpga_manager_ops? The owner within the
ops struct makes more sense to me, it better illustrates what the mutex
is protecting.
> + mgr = ERR_PTR(-ENODEV);
>
> -err_dev:
> - put_device(dev);
> - return ERR_PTR(-ENODEV);
> + mutex_unlock(&mgr->mops_mutex);
> +
> + return mgr;
> }
>
> static int fpga_mgr_dev_match(struct device *dev, const void *data)
> @@ -693,12 +693,18 @@ static int fpga_mgr_dev_match(struct device *dev, const void *data)
> */
> struct fpga_manager *fpga_mgr_get(struct device *dev)
> {
> - struct device *mgr_dev = class_find_device(&fpga_mgr_class, NULL, dev,
> - fpga_mgr_dev_match);
> + struct fpga_manager *mgr;
> + struct device *mgr_dev;
> +
> + mgr_dev = class_find_device(&fpga_mgr_class, NULL, dev, fpga_mgr_dev_match);
> if (!mgr_dev)
> return ERR_PTR(-ENODEV);
>
> - return __fpga_mgr_get(mgr_dev);
> + mgr = __fpga_mgr_get(mgr_dev);
> + if (IS_ERR(mgr))
> + put_device(mgr_dev);
> +
> + return mgr;
> }
> EXPORT_SYMBOL_GPL(fpga_mgr_get);
>
> @@ -711,13 +717,18 @@ EXPORT_SYMBOL_GPL(fpga_mgr_get);
> */
> struct fpga_manager *of_fpga_mgr_get(struct device_node *node)
> {
> - struct device *dev;
> + struct fpga_manager *mgr;
> + struct device *mgr_dev;
>
> - dev = class_find_device_by_of_node(&fpga_mgr_class, node);
> - if (!dev)
> + mgr_dev = class_find_device_by_of_node(&fpga_mgr_class, node);
> + if (!mgr_dev)
> return ERR_PTR(-ENODEV);
>
> - return __fpga_mgr_get(dev);
> + mgr = __fpga_mgr_get(mgr_dev);
> + if (IS_ERR(mgr))
> + put_device(mgr_dev);
> +
> + return mgr;
> }
> EXPORT_SYMBOL_GPL(of_fpga_mgr_get);
>
> @@ -727,7 +738,7 @@ EXPORT_SYMBOL_GPL(of_fpga_mgr_get);
> */
> void fpga_mgr_put(struct fpga_manager *mgr)
> {
> - module_put(mgr->dev.parent->driver->owner);
> + module_put(mgr->mops_owner);
> put_device(&mgr->dev);
> }
> EXPORT_SYMBOL_GPL(fpga_mgr_put);
> @@ -766,9 +777,10 @@ void fpga_mgr_unlock(struct fpga_manager *mgr)
> EXPORT_SYMBOL_GPL(fpga_mgr_unlock);
>
> /**
> - * fpga_mgr_register_full - create and register an FPGA Manager device
> + * __fpga_mgr_register_full - create and register an FPGA Manager device
> * @parent: fpga manager device from pdev
> * @info: parameters for fpga manager
> + * @owner: owner module containing the ops
> *
> * The caller of this function is responsible for calling fpga_mgr_unregister().
> * Using devm_fpga_mgr_register_full() instead is recommended.
> @@ -776,7 +788,8 @@ EXPORT_SYMBOL_GPL(fpga_mgr_unlock);
> * Return: pointer to struct fpga_manager pointer or ERR_PTR()
> */
> struct fpga_manager *
> -fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info)
> +__fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
> + struct module *owner)
> {
> const struct fpga_manager_ops *mops = info->mops;
> struct fpga_manager *mgr;
> @@ -803,6 +816,9 @@ fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *in
> }
>
> mutex_init(&mgr->ref_mutex);
> + mutex_init(&mgr->mops_mutex);
> +
> + mgr->mops_owner = owner;
>
> mgr->name = info->name;
> mgr->mops = info->mops;
> @@ -841,14 +857,15 @@ fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *in
>
> return ERR_PTR(ret);
> }
> -EXPORT_SYMBOL_GPL(fpga_mgr_register_full);
> +EXPORT_SYMBOL_GPL(__fpga_mgr_register_full);
>
> /**
> - * fpga_mgr_register - create and register an FPGA Manager device
> + * __fpga_mgr_register - create and register an FPGA Manager device
> * @parent: fpga manager device from pdev
> * @name: fpga manager name
> * @mops: pointer to structure of fpga manager ops
> * @priv: fpga manager private data
> + * @owner: owner module containing the ops
> *
> * The caller of this function is responsible for calling fpga_mgr_unregister().
> * Using devm_fpga_mgr_register() instead is recommended. This simple
> @@ -859,8 +876,8 @@ EXPORT_SYMBOL_GPL(fpga_mgr_register_full);
> * Return: pointer to struct fpga_manager pointer or ERR_PTR()
> */
> struct fpga_manager *
> -fpga_mgr_register(struct device *parent, const char *name,
> - const struct fpga_manager_ops *mops, void *priv)
> +__fpga_mgr_register(struct device *parent, const char *name,
> + const struct fpga_manager_ops *mops, void *priv, struct module *owner)
> {
> struct fpga_manager_info info = { 0 };
>
> @@ -868,9 +885,9 @@ fpga_mgr_register(struct device *parent, const char *name,
> info.mops = mops;
> info.priv = priv;
>
> - return fpga_mgr_register_full(parent, &info);
> + return __fpga_mgr_register_full(parent, &info, owner);
> }
> -EXPORT_SYMBOL_GPL(fpga_mgr_register);
> +EXPORT_SYMBOL_GPL(__fpga_mgr_register);
>
> /**
> * fpga_mgr_unregister - unregister an FPGA manager
> @@ -888,6 +905,12 @@ void fpga_mgr_unregister(struct fpga_manager *mgr)
> */
> fpga_mgr_fpga_remove(mgr);
>
> + mutex_lock(&mgr->mops_mutex);
> +
> + mgr->mops = NULL;
> +
> + mutex_unlock(&mgr->mops_mutex);
> +
> device_unregister(&mgr->dev);
> }
> EXPORT_SYMBOL_GPL(fpga_mgr_unregister);
> @@ -900,9 +923,10 @@ static void devm_fpga_mgr_unregister(struct device *dev, void *res)
> }
>
> /**
> - * devm_fpga_mgr_register_full - resource managed variant of fpga_mgr_register()
> + * __devm_fpga_mgr_register_full - resource managed variant of fpga_mgr_register()
> * @parent: fpga manager device from pdev
> * @info: parameters for fpga manager
> + * @owner: owner module containing the ops
> *
> * Return: fpga manager pointer on success, negative error code otherwise.
> *
> @@ -910,7 +934,8 @@ static void devm_fpga_mgr_unregister(struct device *dev, void *res)
> * function will be called automatically when the managing device is detached.
> */
> struct fpga_manager *
> -devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info)
> +__devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
> + struct module *owner)
> {
> struct fpga_mgr_devres *dr;
> struct fpga_manager *mgr;
> @@ -919,7 +944,7 @@ devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_inf
> if (!dr)
> return ERR_PTR(-ENOMEM);
>
> - mgr = fpga_mgr_register_full(parent, info);
> + mgr = __fpga_mgr_register_full(parent, info, owner);
> if (IS_ERR(mgr)) {
> devres_free(dr);
> return mgr;
> @@ -930,14 +955,15 @@ devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_inf
>
> return mgr;
> }
> -EXPORT_SYMBOL_GPL(devm_fpga_mgr_register_full);
> +EXPORT_SYMBOL_GPL(__devm_fpga_mgr_register_full);
>
> /**
> - * devm_fpga_mgr_register - resource managed variant of fpga_mgr_register()
> + * __devm_fpga_mgr_register - resource managed variant of fpga_mgr_register()
> * @parent: fpga manager device from pdev
> * @name: fpga manager name
> * @mops: pointer to structure of fpga manager ops
> * @priv: fpga manager private data
> + * @owner: owner module containing the ops
> *
> * Return: fpga manager pointer on success, negative error code otherwise.
> *
> @@ -946,8 +972,9 @@ EXPORT_SYMBOL_GPL(devm_fpga_mgr_register_full);
> * device is detached.
> */
> struct fpga_manager *
> -devm_fpga_mgr_register(struct device *parent, const char *name,
> - const struct fpga_manager_ops *mops, void *priv)
> +__devm_fpga_mgr_register(struct device *parent, const char *name,
> + const struct fpga_manager_ops *mops, void *priv,
> + struct module *owner)
> {
> struct fpga_manager_info info = { 0 };
>
> @@ -955,9 +982,9 @@ devm_fpga_mgr_register(struct device *parent, const char *name,
> info.mops = mops;
> info.priv = priv;
>
> - return devm_fpga_mgr_register_full(parent, &info);
> + return __devm_fpga_mgr_register_full(parent, &info, owner);
> }
> -EXPORT_SYMBOL_GPL(devm_fpga_mgr_register);
> +EXPORT_SYMBOL_GPL(__devm_fpga_mgr_register);
>
> static void fpga_mgr_dev_release(struct device *dev)
> {
> diff --git a/include/linux/fpga/fpga-mgr.h b/include/linux/fpga/fpga-mgr.h
> index 54f63459efd6..967540311462 100644
> --- a/include/linux/fpga/fpga-mgr.h
> +++ b/include/linux/fpga/fpga-mgr.h
> @@ -201,6 +201,8 @@ struct fpga_manager_ops {
> * @state: state of fpga manager
> * @compat_id: FPGA manager id for compatibility check.
> * @mops: pointer to struct of fpga manager ops
> + * @mops_mutex: protects mops from low-level module removal
> + * @mops_owner: module containing the mops
> * @priv: low level driver private date
> */
> struct fpga_manager {
> @@ -210,6 +212,8 @@ struct fpga_manager {
> enum fpga_mgr_states state;
> struct fpga_compat_id *compat_id;
> const struct fpga_manager_ops *mops;
> + struct mutex mops_mutex;
> + struct module *mops_owner;
> void *priv;
> };
>
> @@ -222,6 +226,7 @@ void fpga_image_info_free(struct fpga_image_info *info);
> int fpga_mgr_load(struct fpga_manager *mgr, struct fpga_image_info *info);
>
> int fpga_mgr_lock(struct fpga_manager *mgr);
> +
Why adding a line?
> void fpga_mgr_unlock(struct fpga_manager *mgr);
>
> struct fpga_manager *of_fpga_mgr_get(struct device_node *node);
> @@ -230,18 +235,81 @@ struct fpga_manager *fpga_mgr_get(struct device *dev);
>
> void fpga_mgr_put(struct fpga_manager *mgr);
>
> +/**
> + * fpga_mgr_register_full - create and register an FPGA Manager device
> + * @parent: fpga manager device from pdev
> + * @info: parameters for fpga manager
> + *
> + * The caller of this function is responsible for calling fpga_mgr_unregister().
> + * Using devm_fpga_mgr_register_full() instead is recommended.
> + *
> + * Return: pointer to struct fpga_manager pointer or ERR_PTR()
> + */
No need to duplicate the doc, just remove it.
Same for the rest of code.
> +#define fpga_mgr_register_full(parent, info) \
> + __fpga_mgr_register_full(parent, info, THIS_MODULE)
> +
Delete the line, and ...
> struct fpga_manager *
> -fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info);
> +__fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
> + struct module *owner);
Add a line here, to make the related functions packed.
Same for the rest of code.
> +/**
> + * fpga_mgr_register - create and register an FPGA Manager device
> + * @parent: fpga manager device from pdev
> + * @name: fpga manager name
> + * @mops: pointer to structure of fpga manager ops
> + * @priv: fpga manager private data
> + *
> + * The caller of this function is responsible for calling fpga_mgr_unregister().
> + * Using devm_fpga_mgr_register() instead is recommended. This simple
> + * version of the register function should be sufficient for most users. The
> + * fpga_mgr_register_full() function is available for users that need to pass
> + * additional, optional parameters.
> + *
> + * Return: pointer to struct fpga_manager pointer or ERR_PTR()
> + */
> +#define fpga_mgr_register(parent, name, mops, priv) \
> + __fpga_mgr_register(parent, name, mops, priv, THIS_MODULE)
>
> struct fpga_manager *
> -fpga_mgr_register(struct device *parent, const char *name,
> - const struct fpga_manager_ops *mops, void *priv);
> +__fpga_mgr_register(struct device *parent, const char *name,
> + const struct fpga_manager_ops *mops, void *priv, struct module *owner);
> +
> void fpga_mgr_unregister(struct fpga_manager *mgr);
>
> +/**
> + * devm_fpga_mgr_register_full - resource managed variant of fpga_mgr_register()
> + * @parent: fpga manager device from pdev
> + * @info: parameters for fpga manager
> + *
> + * Return: fpga manager pointer on success, negative error code otherwise.
> + *
> + * This is the devres variant of fpga_mgr_register_full() for which the unregister
> + * function will be called automatically when the managing device is detached.
> + */
> +#define devm_fpga_mgr_register_full(parent, info) \
> + __devm_fpga_mgr_register_full(parent, info, THIS_MODULE)
> +
> struct fpga_manager *
> -devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info);
> +__devm_fpga_mgr_register_full(struct device *parent, const struct fpga_manager_info *info,
> + struct module *owner);
> +/**
> + * devm_fpga_mgr_register - resource managed variant of fpga_mgr_register()
> + * @parent: fpga manager device from pdev
> + * @name: fpga manager name
> + * @mops: pointer to structure of fpga manager ops
> + * @priv: fpga manager private data
> + *
> + * Return: fpga manager pointer on success, negative error code otherwise.
> + *
> + * This is the devres variant of fpga_mgr_register() for which the
> + * unregister function will be called automatically when the managing
> + * device is detached.
> + */
> +#define devm_fpga_mgr_register(parent, name, mops, priv) \
> + __devm_fpga_mgr_register(parent, name, mops, priv, THIS_MODULE)
> +
> struct fpga_manager *
> -devm_fpga_mgr_register(struct device *parent, const char *name,
> - const struct fpga_manager_ops *mops, void *priv);
> +__devm_fpga_mgr_register(struct device *parent, const char *name,
> + const struct fpga_manager_ops *mops, void *priv,
> + struct module *owner);
>
> #endif /*_LINUX_FPGA_MGR_H */
> --
> 2.43.0
>
>
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