diff mbox series

[v2,1/2] module: update dependencies at try_module_get()

Message ID 3c7547d551558c9da02038dda45992f91b1f5141.1651314499.git.mchehab@kernel.org (mailing list archive)
State New
Headers show
Series Let userspace know when snd-hda-intel needs i915 | expand

Commit Message

Mauro Carvalho Chehab April 30, 2022, 10:30 a.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>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
---

See [PATCH v2 0/2] at: https://lore.kernel.org/all/cover.1651314499.git.mchehab@kernel.org/

 include/linux/module.h |  4 +++-
 kernel/module/main.c   | 35 +++++++++++++++++++++++++++++++++--
 2 files changed, 36 insertions(+), 3 deletions(-)

Comments

Greg Kroah-Hartman April 30, 2022, 12:04 p.m. UTC | #1
On Sat, Apr 30, 2022 at 11:30:58AM +0100, Mauro Carvalho Chehab wrote:
> 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>
> Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
> ---
> 
> See [PATCH v2 0/2] at: https://lore.kernel.org/all/cover.1651314499.git.mchehab@kernel.org/
> 
>  include/linux/module.h |  4 +++-
>  kernel/module/main.c   | 35 +++++++++++++++++++++++++++++++++--
>  2 files changed, 36 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 46d4d5f2516e..836851baaad4 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -620,7 +620,9 @@ 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(struct module *module, struct module *this);
> +
> +#define try_module_get(mod) __try_module_get(mod, THIS_MODULE)
>  
>  extern void module_put(struct module *module);
>  
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 05a42d8fcd7a..9f4416381e65 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -631,6 +631,35 @@ static int ref_module(struct module *a, struct module *b)
>  	return 0;
>  }
>  
> +static int ref_module_dependency(struct module *mod,
> +				       struct module *this)

This can be on one line, right?

> +{
> +	int ret;
> +
> +	if (!this || !this->name) {
> +		return -EINVAL;
> +	}

Did you run checkpatch on this?  Please do :)

> +
> +	if (mod == this)
> +		return 0;

How can this happen?

When people mistakenly call try_module_get(THIS_MODULE)?  We should
throw up a big warning when that happens anyway as that's always wrong.

But that's a different issue from this change, sorry for the noise.

> +
> +	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);

Meta comment, why do we only create links if we can unload things?

thanks,

greg k-h
Mauro Carvalho Chehab April 30, 2022, 1:38 p.m. UTC | #2
Em Sat, 30 Apr 2022 14:04:59 +0200
Greg KH <gregkh@linuxfoundation.org> escreveu:

> On Sat, Apr 30, 2022 at 11:30:58AM +0100, Mauro Carvalho Chehab wrote:

> Did you run checkpatch on this?  Please do :)
> 
> > +
> > +	if (mod == this)
> > +		return 0;  
> 
> How can this happen?
> When people mistakenly call try_module_get(THIS_MODULE)?  

Yes. There are lots of place where this is happening:

	$ git grep try_module_get\(THIS_MODULE|wc -l
	82

> We should
> throw up a big warning when that happens anyway as that's always wrong.
> 
> But that's a different issue from this change, sorry for the noise.

It sounds very weird to use try_module_get(THIS_MODULE).

We could add a WARN_ON() there - or something similar - but I would do it 
on a separate patch.

> 
> > +
> > +	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);  
> 
> Meta comment, why do we only create links if we can unload things?

Good question. I don't know for certain. This is the already existing 
pattern at add_usage_links() - see kernel/module/sysfs.c.

Also, lsmod uses sysfs links when showing dependencies.

Regards,
Mauro
David Laight May 1, 2022, 1:23 p.m. UTC | #3
From: Mauro Carvalho Chehab
> Sent: 30 April 2022 14:38
> 
> Em Sat, 30 Apr 2022 14:04:59 +0200
> Greg KH <gregkh@linuxfoundation.org> escreveu:
> 
> > On Sat, Apr 30, 2022 at 11:30:58AM +0100, Mauro Carvalho Chehab wrote:
> 
> > Did you run checkpatch on this?  Please do :)
> >
> > > +
> > > +	if (mod == this)
> > > +		return 0;
> >
> > How can this happen?
> > When people mistakenly call try_module_get(THIS_MODULE)?
> 
> Yes. There are lots of place where this is happening:
> 
> 	$ git grep try_module_get\(THIS_MODULE|wc -l
> 	82
> 
> > We should
> > throw up a big warning when that happens anyway as that's always wrong.
> >
> > But that's a different issue from this change, sorry for the noise.
> 
> It sounds very weird to use try_module_get(THIS_MODULE).
> 
> We could add a WARN_ON() there - or something similar - but I would do it
> on a separate patch.

You could add a compile-time check.
But a run-time one seems unnecessary.
Clearly try_module_get(THIS_MODULE) usually succeeds.

I think I can invent a case where it can fail:
The module count must be zero, and a module unload in progress.
The thread doing the unload is blocked somewhere.
Another thread makes a callback into the module for some request
that (for instance) would need to create a kernel thread.
It tries to get a reference for the thread.
So try_module_get(THIS_MODULE) is the right call - and will fail here.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
diff mbox series

Patch

diff --git a/include/linux/module.h b/include/linux/module.h
index 46d4d5f2516e..836851baaad4 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -620,7 +620,9 @@  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(struct module *module, struct module *this);
+
+#define try_module_get(mod) __try_module_get(mod, THIS_MODULE)
 
 extern void module_put(struct module *module);
 
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 05a42d8fcd7a..9f4416381e65 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -631,6 +631,35 @@  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)
 {
@@ -841,7 +870,7 @@  void __module_get(struct module *module)
 }
 EXPORT_SYMBOL(__module_get);
 
-bool try_module_get(struct module *module)
+bool __try_module_get(struct module *module, struct module *this)
 {
 	bool ret = true;
 
@@ -856,9 +885,11 @@  bool try_module_get(struct module *module)
 
 		preempt_enable();
 	}
+	if (ret)
+		ref_module_dependency(module, this);
 	return ret;
 }
-EXPORT_SYMBOL(try_module_get);
+EXPORT_SYMBOL(__try_module_get);
 
 void module_put(struct module *module)
 {