[PATCH v3 1/2] module: update dependencies at try_module_get()

Mauro Carvalho Chehab
2022-04-30T13:43:29Z

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 v3 0/2] at: https://lore.kernel.org/all/cover.1651326000.git.mchehab@kernel.org/

include/linux/module.h | 4 +++-
kernel/module/main.c | 33 +++++++++++++++++++++++++++++++--
2 files changed, 34 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..d63ebf52392b 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -631,6 +631,33 @@ 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)
{
@@ -841,7 +868,7 @@ 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 +883,11 @@ 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)
{
--
2.35.1