Subject: [PATCH 06/28] module: Use RCU in find_module_all().
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Wed, 8 Jan 2025 10:04:35 +0100

The modules list and module::kallsyms can be accessed under RCU
assumption.

Remove module_assert_mutex_or_preempt() from find_module_all() so it can
be used under RCU protection without warnings. Update its callers to use
RCU protection instead of preempt_disable().

Cc: Jiri Kosina <[email-masked]>
Cc: Joe Lawrence <[email-masked]>
Cc: Josh Poimboeuf <[email-masked]>
Cc: Masami Hiramatsu <[email-masked]>
Cc: Mathieu Desnoyers <[email-masked]>
Cc: Miroslav Benes <[email-masked]>
Cc: Petr Mladek <[email-masked]>
Cc: Steven Rostedt <[email-masked]>
Cc: [email-masked]
Cc: [email-masked]
Reviewed-by: Petr Mladek <[email-masked]>
Acked-by: Peter Zijlstra (Intel) <[email-masked]>
Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 include/linux/module.h      |    2 +-
 kernel/livepatch/core.c     |    4 +---
 kernel/module/kallsyms.c    |    1 +
 kernel/module/main.c        |    6 ++----
 kernel/trace/trace_kprobe.c |    9 +++------
 5 files changed, 8 insertions(+), 14 deletions(-)

--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -666,7 +666,7 @@ static inline bool within_module(unsigne
 	return within_module_init(addr, mod) || within_module_core(addr, mod);
 }
 
-/* Search for module by name: must be in a RCU-sched critical section. */
+/* Search for module by name: must be in a RCU critical section. */
 struct module *find_module(const char *name);
 
 extern void __noreturn __module_put_and_kthread_exit(struct module *mod,
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -59,7 +59,7 @@ static void klp_find_object_module(struc
 	if (!klp_is_module(obj))
 		return;
 
-	rcu_read_lock_sched();
+	guard(rcu)();
 	/*
 	 * We do not want to block removal of patched modules and therefore
 	 * we do not take a reference here. The patches are removed by
@@ -75,8 +75,6 @@ static void klp_find_object_module(struc
 	 */
 	if (mod && mod->klp_alive)
 		obj->mod = mod;
-
-	rcu_read_unlock_sched();
 }
 
 static bool klp_initialized(void)
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -450,6 +450,7 @@ unsigned long module_kallsyms_lookup_nam
 	unsigned long ret;
 
 	/* Don't lock: we're in enough trouble already. */
+	guard(rcu)();
 	preempt_disable();
 	ret = __module_kallsyms_lookup_name(name);
 	preempt_enable();
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -374,16 +374,14 @@ bool find_symbol(struct find_symbol_arg
 }
 
 /*
- * Search for module by name: must hold module_mutex (or preempt disabled
- * for read-only access).
+ * Search for module by name: must hold module_mutex (or RCU for read-only
+ * access).
  */
 struct module *find_module_all(const char *name, size_t len,
 			       bool even_unformed)
 {
 	struct module *mod;
 
-	module_assert_mutex_or_preempt();
-
 	list_for_each_entry_rcu(mod, &modules, list,
 				lockdep_is_held(&module_mutex)) {
 		if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -124,9 +124,8 @@ static nokprobe_inline bool trace_kprobe
 	if (!p)
 		return true;
 	*p = '\0';
-	rcu_read_lock_sched();
-	ret = !!find_module(tk->symbol);
-	rcu_read_unlock_sched();
+	scoped_guard(rcu)
+		ret = !!find_module(tk->symbol);
 	*p = ':';
 
 	return ret;
@@ -796,12 +795,10 @@ static struct module *try_module_get_by_
 {
 	struct module *mod;
 
-	rcu_read_lock_sched();
+	guard(rcu)();
 	mod = find_module(name);
 	if (mod && !try_module_get(mod))
 		mod = NULL;
-	rcu_read_unlock_sched();
-
 	return mod;
 }
 #else