Sometimes, device drivers are bound using indirect references,
which is not visible when looking at /proc/modules or lsmod.
Add a function to allow setting up module references for such
cases.
Reviewed-by: Dan Williams <[email protected]>
Signed-off-by: Mauro Carvalho Chehab <[email protected]>
---
See [PATCH 0/2] at: https://lore.kernel.org/all/[email protected]/
include/linux/module.h | 7 +++++++
kernel/module/main.c | 31 +++++++++++++++++++++++++++++++
2 files changed, 38 insertions(+)
diff --git a/include/linux/module.h b/include/linux/module.h
index 46d4d5f2516e..be74f807e41d 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -596,6 +596,8 @@ static inline bool within_module(unsigned long addr, const struct module *mod)
/* Search for module by name: must be in a RCU-sched critical section. */
struct module *find_module(const char *name);
+int module_add_named_dependency(const char *name, struct module *this);
+
/* Returns 0 and fills in value, defined and namebuf, or -ERANGE if
symnum out of range. */
int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
@@ -772,6 +774,11 @@ static inline int lookup_module_symbol_attrs(unsigned long addr, unsigned long *
return -ERANGE;
}
+static inline int module_add_named_dependency(const char *name, struct module *this)
+{
+ return 0;
+}
+
static inline int module_get_kallsym(unsigned int symnum, unsigned long *value,
char *type, char *name,
char *module_name, int *exported)
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 05a42d8fcd7a..dbd577ccc38c 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -631,6 +631,37 @@ static int ref_module(struct module *a, struct module *b)
return 0;
}
+int module_add_named_dependency(const char *name, struct module *this)
+{
+ struct module *mod;
+ int ret;
+
+ if (!name || !this || !this->name) {
+ return -EINVAL;
+ }
+
+ mutex_lock(&module_mutex);
+ mod = find_module(name);
+ if (!mod) {
+ ret = -EINVAL;
+ goto ret;
+ }
+
+ ret = ref_module(this, mod);
+ if (ret)
+ goto ret;
+
+#ifdef CONFIG_MODULE_UNLOAD
+ ret = sysfs_create_link(mod->holders_dir,
+ &this->mkobj.kobj, this->name);
+#endif
+
+ret:
+ mutex_unlock(&module_mutex);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(module_add_named_dependency);
+
/* Clear the unload stuff of the module. */
static void module_unload_free(struct module *mod)
{
--
2.35.1
HI Greg,
Em Fri, 29 Apr 2022 10:30:33 +0200
Greg KH <[email protected]> escreveu:
> On Fri, Apr 29, 2022 at 09:07:57AM +0100, Mauro Carvalho Chehab wrote:
> > Hi Daniel,
> >
> > Em Fri, 29 Apr 2022 09:54:10 +0200
> > Daniel Vetter <[email protected]> escreveu:
> >
> > > On Fri, Apr 29, 2022 at 07:31:15AM +0100, Mauro Carvalho Chehab wrote:
> > > > Sometimes, device drivers are bound using indirect references,
> > > > which is not visible when looking at /proc/modules or lsmod.
> > > >
> > > > Add a function to allow setting up module references for such
> > > > cases.
> > > >
> > > > Reviewed-by: Dan Williams <[email protected]>
> > > > Signed-off-by: Mauro Carvalho Chehab <[email protected]>
> > >
> > > This sounds like duct tape at the wrong level. We should have a
> > > device_link connecting these devices, and maybe device_link internally
> > > needs to make sure the respective driver modules stay around for long
> > > enough too. But open-coding this all over the place into every driver that
> > > has some kind of cross-driver dependency sounds terrible.
> > >
> > > Or maybe the bug is that the snd driver keeps accessing the hw/component
> > > side when that is just plain gone. Iirc there's still fundamental issues
> > > there on the sound side of things, which have been attempted to paper over
> > > by timeouts and stuff like that in the past instead of enforcing a hard
> > > link between the snd and i915 side.
> >
> > I agree with you that the device link between snd-hda and the DRM driver
> > should properly handle unbinding on both directions. This is something
> > that require further discussions with ALSA and DRM people, and we should
> > keep working on it.
> >
> > Yet, the binding between those drivers do exist, but, despite other
> > similar inter-driver bindings being properly reported by lsmod, this one
> > is invisible for userspace.
> >
> > What this series does is to make such binding visible. As simple as that.
>
> It also increases the reference count, and creates a user/kernel api
> with the symlinks, right? Will the reference count increase prevent the
> modules from now being unloadable?
>
> This feels like a very "weak" link between modules that should not be
> needed if reference counting is implemented properly (so that things are
> cleaned up in the correct order.)
The refcount increment exists even without this patch, as
hda_component_master_bind() at sound/hda/hdac_component.c uses
try_module_get() when it creates the device link.
This series won't change anything with that regards. The only difference
is that it will now properly report userspace that snd-hda will be
using something inside the DRM driver (basically, it uses the DRM driver
to power-control the HDA hardware on modern CPU/GPUs).
-
Btw, this is not the only case where userspace invisible bindings between
two driver happen within the Kernel. On media, DVB drivers attach
the frontend/tuner drivers using I2C bus on a way where lsmod doesn't
current report any dependencies. See, for instance, PCTV 290e driver
(partial) dependency chain:
$ lsmod
Module Size Used by
rc_pinnacle_pctv_hd 16384 0
em28xx_rc 20480 0
tda18271 53248 1
cxd2820r 45056 1
em28xx_dvb 36864 0
dvb_core 155648 2 cxd2820r,em28xx_dvb
em28xx 106496 2 em28xx_rc,em28xx_dvb
tveeprom 28672 1 em28xx
videobuf2_vmalloc 20480 1 uvcvideo
videobuf2_memops 20480 1 videobuf2_vmalloc
videobuf2_common 69632 4 videobuf2_vmalloc,videobuf2_v4l2,uvcvideo,videobuf2_memops
videodev 266240 4 videobuf2_v4l2,uvcvideo,videobuf2_common,em28xx
mc 65536 6 videodev,videobuf2_v4l2,uvcvideo,dvb_core,videobuf2_common,em28xx
In the above example, tda18271 is an I2C tuner driver which talks
to the hardware via the I2C bus registered by the em28xx driver.
It is loaded during em28xx probing time.
Again, lsmod doesn't show such dependencies. One can't remove the
tuner driver without first removing the em28xx driver, which is
the one that increments its refcount.
-
Back to the snd-hda issue, the problem is not with refcount. It is, instead,
to provide a way for userspace to know what's the correct order to
remove/unbind modules.
Regards,
Mauro
On Fri, Apr 29, 2022 at 07:31:15AM +0100, Mauro Carvalho Chehab wrote:
> Sometimes, device drivers are bound using indirect references,
> which is not visible when looking at /proc/modules or lsmod.
>
> Add a function to allow setting up module references for such
> cases.
>
> Reviewed-by: Dan Williams <[email protected]>
> Signed-off-by: Mauro Carvalho Chehab <[email protected]>
This sounds like duct tape at the wrong level. We should have a
device_link connecting these devices, and maybe device_link internally
needs to make sure the respective driver modules stay around for long
enough too. But open-coding this all over the place into every driver that
has some kind of cross-driver dependency sounds terrible.
Or maybe the bug is that the snd driver keeps accessing the hw/component
side when that is just plain gone. Iirc there's still fundamental issues
there on the sound side of things, which have been attempted to paper over
by timeouts and stuff like that in the past instead of enforcing a hard
link between the snd and i915 side.
Adding Greg for device model questions like this.
-Daniel
> ---
>
> See [PATCH 0/2] at: https://lore.kernel.org/all/[email protected]/
>
> include/linux/module.h | 7 +++++++
> kernel/module/main.c | 31 +++++++++++++++++++++++++++++++
> 2 files changed, 38 insertions(+)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 46d4d5f2516e..be74f807e41d 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -596,6 +596,8 @@ static inline bool within_module(unsigned long addr, const struct module *mod)
> /* Search for module by name: must be in a RCU-sched critical section. */
> struct module *find_module(const char *name);
>
> +int module_add_named_dependency(const char *name, struct module *this);
> +
> /* Returns 0 and fills in value, defined and namebuf, or -ERANGE if
> symnum out of range. */
> int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
> @@ -772,6 +774,11 @@ static inline int lookup_module_symbol_attrs(unsigned long addr, unsigned long *
> return -ERANGE;
> }
>
> +static inline int module_add_named_dependency(const char *name, struct module *this)
> +{
> + return 0;
> +}
> +
> static inline int module_get_kallsym(unsigned int symnum, unsigned long *value,
> char *type, char *name,
> char *module_name, int *exported)
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 05a42d8fcd7a..dbd577ccc38c 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -631,6 +631,37 @@ static int ref_module(struct module *a, struct module *b)
> return 0;
> }
>
> +int module_add_named_dependency(const char *name, struct module *this)
> +{
> + struct module *mod;
> + int ret;
> +
> + if (!name || !this || !this->name) {
> + return -EINVAL;
> + }
> +
> + mutex_lock(&module_mutex);
> + mod = find_module(name);
> + if (!mod) {
> + ret = -EINVAL;
> + goto ret;
> + }
> +
> + ret = ref_module(this, mod);
> + if (ret)
> + goto ret;
> +
> +#ifdef CONFIG_MODULE_UNLOAD
> + ret = sysfs_create_link(mod->holders_dir,
> + &this->mkobj.kobj, this->name);
> +#endif
> +
> +ret:
> + mutex_unlock(&module_mutex);
> + return ret;
> +}
> +EXPORT_SYMBOL_GPL(module_add_named_dependency);
> +
> /* Clear the unload stuff of the module. */
> static void module_unload_free(struct module *mod)
> {
> --
> 2.35.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch