[PATCH v2] cgroup: Fix compilation issue due to cgroup_mutex not being exported

[gaoxu]

When adding folio_memcg function call in the zram module for
Android 16-6.12, the following error occurs during compilation:
ERROR: modpost: "cgroup_mutex" [../soc-repo/zram.ko] undefined!

This error is caused by the indirect call to lockdep_is_held(&cgroup_mutex)
within folio_memcg. The export setting for cgroup_mutex is controlled by
the CONFIG_PROVE_RCU macro. If CONFIG_LOCKDEP is enabled while
CONFIG_PROVE_RCU is not, this compilation error will occur.

To resolve this issue, add a parallel macro CONFIG_LOCKDEP control to
ensure cgroup_mutex is properly exported when needed.

Signed-off-by: gao xu <gaoxu2@xxxxxxxxx>
---
v1 -> v2: update the notes of the description above DEFINE_MUTEX(cgroup_mutex)
per Kamalesh's suggestion.
---
 kernel/cgroup/cgroup.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 447ac857e..c1bc51058 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -84,13 +84,13 @@
  * css_set_lock protects task->cgroups pointer, the list of css_set
  * objects, and the chain of tasks off each css_set.
  *
- * These locks are exported if CONFIG_PROVE_RCU so that accessors in
- * cgroup.h can use them for lockdep annotations.
+ * These locks are exported if CONFIG_PROVE_RCU or CONFIG_LOCKDEP so that
+ * accessors in cgroup.h can use them for lockdep annotations.
  */
 DEFINE_MUTEX(cgroup_mutex);
 DEFINE_SPINLOCK(css_set_lock);
 
-#ifdef CONFIG_PROVE_RCU
+#if (defined CONFIG_PROVE_RCU || defined CONFIG_LOCKDEP)
 EXPORT_SYMBOL_GPL(cgroup_mutex);
 EXPORT_SYMBOL_GPL(css_set_lock);
 #endif
-- 
2.17.1