diff mbox series

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

Message ID ad2a9fe66cf502e2e2e2325f1f04d0fae36aa82b.1651348913.git.mchehab@kernel.org
State Superseded
Headers show
Series Let userspace know when snd-hda-intel needs i915 | expand

Commit Message

Mauro Carvalho Chehab April 30, 2022, 8:04 p.m. UTC 
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(-)

Comments

Mauro Carvalho Chehab May 9, 2022, 4:56 p.m. UTC | #1 
Em Thu, 5 May 2022 23:35:29 +0200
Andi Shyti <andi.shyti@linux.intel.com> escreveu:

> Hi Mauro,
> 
> [...]
> 
> > +static int ref_module_dependency(struct module *mod, struct module *this)
> > +{
> > +	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
> > +	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)
> >  {
> > -	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);  
> 
> do we care about the return value here?

I don't think it should care about the return value, as a failure to
create a sysfs node for the holder or to add it to the holders list
is not fatal: modules can still continue working without that.

Also, I opted to be conservative here: currently, not creating these
doesn't cause try_module_get() to fail. I'm not sure what would be the
impact if this starts to fail.

So, right now, I'm opting to just ignore the return value. Perhaps
in the future this could a warning (similarly to what sysfs create
link does).

Regards,
Mauro

> 
> Andi
> 
> >  
> > -		preempt_enable();
> > -	}
> >  	return ret;
> >  }
> > -EXPORT_SYMBOL(try_module_get);
> > +EXPORT_SYMBOL(try_module_get_owner);
> >  
> >  void module_put(struct module *module)
> >  {
> > -- 
> > 2.35.1  



Thanks,
Mauro
diff mbox series

Patch

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);
 
 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)
+{
+	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
+	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)
 {
-	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)
 {