module: Use RCU in find_module_all().

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 protected]>
Cc: Joe Lawrence <[email protected]>
Cc: Josh Poimboeuf <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Miroslav Benes <[email protected]>
Cc: Petr Mladek <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Sebastian Andrzej Siewior <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Reviewed-by: Petr Mladek <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Petr Pavlu <[email protected]>

Author: Sebastian Andrzej Siewior

include/linux/module.h

@@ -666,7 +666,7 @@ static inline bool within_module(unsigned long addr, const struct module *mod)
 	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,

kernel/livepatch/core.c

@@ -59,7 +59,7 @@ static void klp_find_object_module(struct klp_object *obj)
 	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(struct klp_object *obj)
 	 */
 	if (mod && mod->klp_alive)
 		obj->mod = mod;
-
-	rcu_read_unlock_sched();
 }
 
 static bool klp_initialized(void)

kernel/module/kallsyms.c

@@ -450,6 +450,7 @@ unsigned long module_kallsyms_lookup_name(const char *name)
 	unsigned long ret;
 
 	/* Don't lock: we're in enough trouble already. */
+	guard(rcu)();
 	preempt_disable();
 	ret = __module_kallsyms_lookup_name(name);
 	preempt_enable();

kernel/module/main.c

@@ -374,16 +374,14 @@ bool find_symbol(struct find_symbol_arg *fsa)
 }
 
 /*
- * 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)

kernel/trace/trace_kprobe.c

@@ -124,9 +124,8 @@ static nokprobe_inline bool trace_kprobe_module_exist(struct trace_kprobe *tk)
 	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_name(const char *name)
 {
 	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