[PATCH v6 3/4] module: set holders when symbol_get() is used

[Mauro Carvalho Chehab <mchehab@kernel.org>]

Some Kernel modules use symbol_get() or symbol_request() in order
to bind into other drivers. That's the case, for instance, of
media dvb drivers that hook the frontend drivers via I2C using
dvb_attach() macro.

When such bindings happen, one needs first to unload/unbind the
driver that got the symbol before being able to unload/unbind the
module that contains the needed symbol.

Add a logic to document it via /proc/modules and via lsmod.

Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>
---

See [PATCH v6 0/4] at: https://lore.kernel.org/all/cover.1652113087.git.mchehab@kernel.org/

 drivers/mtd/chips/gen_probe.c           | 4 ++--
 include/linux/module.h                  | 4 ++--
 kernel/module/main.c                    | 3 ++-
 samples/hw_breakpoint/data_breakpoint.c | 2 +-
 4 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/chips/gen_probe.c b/drivers/mtd/chips/gen_probe.c
index 4d4f97841016..f1e97633ac09 100644
--- a/drivers/mtd/chips/gen_probe.c
+++ b/drivers/mtd/chips/gen_probe.c
@@ -208,10 +208,10 @@ static inline struct mtd_info *cfi_cmdset_unknown(struct map_info *map,
 	if (!probename)
 		return NULL;
 
-	probe_function = __symbol_get(probename);
+	probe_function = __symbol_get(probename, THIS_MODULE);
 	if (!probe_function) {
 		request_module("cfi_cmdset_%4.4X", type);
-		probe_function = __symbol_get(probename);
+		probe_function = __symbol_get(probename, THIS_MODULE);
 	}
 	kfree(probename);
 
diff --git a/include/linux/module.h b/include/linux/module.h
index a66b9be92ef5..07a77c2618b5 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -298,8 +298,8 @@ struct notifier_block;
 
 extern int modules_disabled; /* for sysctl */
 /* Get/put a kernel symbol (calls must be symmetric) */
-void *__symbol_get(const char *symbol);
-#define symbol_get(x) ((typeof(&x))(__symbol_get(__stringify(x))))
+void *__symbol_get(const char *symbol, struct module *this);
+#define symbol_get(x) ((typeof(&x))(__symbol_get(__stringify(x), THIS_MODULE)))
 
 /* modules using other modules: kdb wants to see this. */
 struct module_use {
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 6044aeba0f18..ec1baa67d6e7 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -1259,7 +1259,7 @@ static void free_module(struct module *mod)
 #endif
 }
 
-void *__symbol_get(const char *symbol)
+void *__symbol_get(const char *symbol, struct module *this)
 {
 	struct find_symbol_arg fsa = {
 		.name	= symbol,
@@ -1273,6 +1273,7 @@ void *__symbol_get(const char *symbol)
 		return NULL;
 	}
 	preempt_enable();
+	ref_module_dependency(fsa.owner, this);
 	return (void *)kernel_symbol_value(fsa.sym);
 }
 EXPORT_SYMBOL_GPL(__symbol_get);
diff --git a/samples/hw_breakpoint/data_breakpoint.c b/samples/hw_breakpoint/data_breakpoint.c
index 418c46fe5ffc..30b3261a894b 100644
--- a/samples/hw_breakpoint/data_breakpoint.c
+++ b/samples/hw_breakpoint/data_breakpoint.c
@@ -41,7 +41,7 @@ static int __init hw_break_module_init(void)
 {
 	int ret;
 	struct perf_event_attr attr;
-	void *addr = __symbol_get(ksym_name);
+	void *addr = __symbol_get(ksym_name, THIS_MODULE);
 
 	if (!addr)
 		return -ENXIO;
-- 
2.35.3