Re: [PATCH v5 1/2] module: update dependencies at try_module_get()

Le 30/04/2022 à 22:04, Mauro Carvalho Chehab a écrit :

Sometimes, device drivers are bound into each other via try_module_get(), making such references invisible when looking at /proc/modules or lsmod.

Add a function to allow setting up module references for such cases, and call it when try_module_get() is used.

Reviewed-by: Dan Williams dan.j.williams@intel.com Reviewed-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Mauro Carvalho Chehab mchehab@kernel.org

---

See [PATCH v5 0/2] at: https://lore.kernel.org/all/cover.1651348913.git.mchehab@kernel.org/

include/linux/module.h | 8 ++++-- kernel/module/main.c | 65 +++++++++++++++++++++++++++++++++--------- 2 files changed, 56 insertions(+), 17 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h index 46d4d5f2516e..3d9d38c426b4 100644 --- a/include/linux/module.h +++ b/include/linux/module.h @@ -620,12 +620,12 @@ extern void __module_get(struct module *module);

/* This is the Right Way to get a module: if it fails, it's being removed,

• so pretend it's not there. */

-extern bool try_module_get(struct module *module); +extern bool try_module_get_owner(struct module *module, struct module *this);

You may want to remove that useless 'extern'.

'checkpatch --strict' will likely tell you to do so.

extern void module_put(struct module *module);

#else /*!CONFIG_MODULE_UNLOAD*/ -static inline bool try_module_get(struct module *module) +static inline bool try_module_get_owner(struct module *module, struct module *this) { return !module || module_is_live(module); } @@ -740,7 +740,7 @@ static inline void __module_get(struct module *module) { }

-static inline bool try_module_get(struct module *module) +static inline bool try_module_get_owner(struct module *module, struct module *this) { return true; } @@ -875,6 +875,8 @@ static inline bool module_sig_ok(struct module *module) } #endif /* CONFIG_MODULE_SIG */

+#define try_module_get(mod) try_module_get_owner(mod, THIS_MODULE)

• int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *, struct module *, unsigned long), void *data);

diff --git a/kernel/module/main.c b/kernel/module/main.c index 05a42d8fcd7a..218c4308bb7a 100644 --- a/kernel/module/main.c +++ b/kernel/module/main.c @@ -150,6 +150,24 @@ int unregister_module_notifier(struct notifier_block *nb) } EXPORT_SYMBOL(unregister_module_notifier);

+static bool __try_module_get(struct module *module) +{

• bool ret = true;
• if (module) {

• preempt_disable();
  

• /* Note: here, we can fail to get a reference */
  

• if (likely(module_is_live(module) &&
  

• 	   atomic_inc_not_zero(&module->refcnt) != 0))
  

• 	trace_module_get(module, _RET_IP_);
  

• else
  

• 	ret = false;
  

• preempt_enable();
  

• }
• return ret;

+}

• /*
  • We require a truly strong try_module_get(): 0 means success.
  • Otherwise an error is returned due to ongoing or failed

@@ -160,7 +178,7 @@ static inline int strong_try_module_get(struct module *mod) BUG_ON(mod && mod->state == MODULE_STATE_UNFORMED); if (mod && mod->state == MODULE_STATE_COMING) return -EBUSY;

• if (try_module_get(mod))

• if (__try_module_get(mod)) return 0; else return -ENOENT;

@@ -631,6 +649,33 @@ static int ref_module(struct module *a, struct module *b) return 0; }

+static int ref_module_dependency(struct module *mod, struct module *this)

What is 'this' ? Can we give it a more precise name ? Is it a child, a parent, a owner, something else ?

+{

• int ret;
• if (!this || !this->name)

• return -EINVAL;
  

• if (mod == this)

• return 0;
  

• mutex_lock(&module_mutex);
• ret = ref_module(this, mod);

+#ifdef CONFIG_MODULE_UNLOAD

Looks like that #ifdef could be avoided and replaced by IS_ENABLED(CONFIG_MODULE_UNLOAD)

Something like:

if (!IS_ENABLED(CONFIG_MODULE_UNLOAD) || ret) goto ret;

• if (ret)

• goto ret;
  

• ret = sysfs_create_link(mod->holders_dir,

• 		&this->mkobj.kobj, this->name);
  

+#endif

+ret:

• mutex_unlock(&module_mutex);
• return ret;

+}

• /* Clear the unload stuff of the module. */ static void module_unload_free(struct module *mod) {

@@ -841,24 +886,16 @@ void __module_get(struct module *module) } EXPORT_SYMBOL(__module_get);

-bool try_module_get(struct module *module) +bool try_module_get_owner(struct module *module, struct module *this)

Same here, what is 'this' exactly ?

{

• bool ret = true;

• int ret = __try_module_get(module);

• if (module) {

• preempt_disable();
  

• /* Note: here, we can fail to get a reference */
  

• if (likely(module_is_live(module) &&
  

• 	   atomic_inc_not_zero(&module->refcnt) != 0))
  

• 	trace_module_get(module, _RET_IP_);
  

• else
  

• 	ret = false;
  

• if (ret)

• ref_module_dependency(module, this);
  
  

• preempt_enable();
  

• } return ret; }

-EXPORT_SYMBOL(try_module_get); +EXPORT_SYMBOL(try_module_get_owner);

void module_put(struct module *module) {