linux-kernel - [PATCH] sysctl: Convert locking comments to lockdep assertions

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Message-Id: <20240629-sysctl-lockdep-v1-1-69196ce85225@weissschuh.net>
Date: Sat, 29 Jun 2024 19:24:31 +0200
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <kees@...nel.org>, 
 Joel Granados <j.granados@...sung.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH] sysctl: Convert locking comments to lockdep assertions

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@...ssschuh.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@...ssschuh.net>