The assertions work as well as the comment to inform developers about
locking expectations.
Additionally they are validated by lockdep at runtime, making sure the
expectations are met.

Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
---
Tested against the sysctl selftests and normal desktop usage.
---
 fs/proc/proc_sysctl.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index b1c2c0b82116..1d9d789fbd3e 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -17,6 +17,7 @@
 #include <linux/bpf-cgroup.h>
 #include <linux/mount.h>
 #include <linux/kmemleak.h>
+#include <linux/lockdep.h>
 #include "internal.h"
 
 #define list_for_each_table_entry(entry, header)	\
@@ -104,7 +105,6 @@ static int namecmp(const char *name1, int len1, const char *name2, int len2)
 	return cmp;
 }
 
-/* Called under sysctl_lock */
 static struct ctl_table *find_entry(struct ctl_table_header **phead,
 	struct ctl_dir *dir, const char *name, int namelen)
 {
@@ -112,6 +112,8 @@ static struct ctl_table *find_entry(struct ctl_table_header **phead,
 	struct ctl_table *entry;
 	struct rb_node *node = dir->root.rb_node;
 
+	lockdep_assert_held(&sysctl_lock);
+
 	while (node)
 	{
 		struct ctl_node *ctl_node;
@@ -258,18 +260,20 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
 	return err;
 }
 
-/* called under sysctl_lock */
 static int use_table(struct ctl_table_header *p)
 {
+	lockdep_assert_held(&sysctl_lock);
+
 	if (unlikely(p->unregistering))
 		return 0;
 	p->used++;
 	return 1;
 }
 
-/* called under sysctl_lock */
 static void unuse_table(struct ctl_table_header *p)
 {
+	lockdep_assert_held(&sysctl_lock);
+
 	if (!--p->used)
 		if (unlikely(p->unregistering))
 			complete(p->unregistering);
@@ -280,9 +284,11 @@ static void proc_sys_invalidate_dcache(struct ctl_table_header *head)
 	proc_invalidate_siblings_dcache(&head->inodes, &sysctl_lock);
 }
 
-/* called under sysctl_lock, will reacquire if has to wait */
 static void start_unregistering(struct ctl_table_header *p)
 {
+	/* will reacquire if has to wait */
+	lockdep_assert_held(&sysctl_lock);
+
 	/*
 	 * if p->used is 0, nobody will ever touch that entry again;
 	 * we'll eliminate all paths to it before dropping sysctl_lock

---
base-commit: 27b31deb900dfcec60820d8d3e48f6de9ae9a18e
change-id: 20240629-sysctl-lockdep-26c90b73a786

Best regards,
-- 
Thomas Weißschuh <linux@weissschuh.net>

On Sat, Jun 29, 2024 at 07:24:31PM +0200, Thomas Weißschuh wrote:
> The assertions work as well as the comment to inform developers about
> locking expectations.
> Additionally they are validated by lockdep at runtime, making sure the
> expectations are met.

Sorry for the late reply (was in PTO). Will put this to sysctl-testing
so I can queue it for 6.13. It is a bit late to put it into 6.12.

Best and thx for the patch

-- 

Joel Granados