From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 8 Jan 2025 10:04:43 +0100
Subject: [PATCH 14/28] module: Use RCU in all users of __module_address().

__module_address() can be invoked within a RCU section, there is no
requirement to have preemption disabled.

Replace the preempt_disable() section around __module_address() with
RCU.

Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20250108090457.512198-15-bigeasy@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/kallsyms.h |    3 +--
 kernel/module/kallsyms.c |    5 +----
 kernel/module/main.c     |    9 ++-------
 3 files changed, 4 insertions(+), 13 deletions(-)

@ include/linux/kallsyms.h:58 @ static inline void *dereference_symbol_d
 	if (is_ksym_addr((unsigned long)ptr))
 		return ptr;
 
-	preempt_disable();
+	guard(rcu)();
 	mod = __module_address((unsigned long)ptr);
 
 	if (mod)
 		ptr = dereference_module_function_descriptor(mod, ptr);
-	preempt_enable();
 #endif
 	return ptr;
 }
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@ include/linux/kallsyms.h:319 @ void * __weak dereference_module_functio
 
 /*
  * For kallsyms to ask for address resolution.  NULL means not found.  Careful
- * not to lock to avoid deadlock on oopses, simply disable preemption.
+ * not to lock to avoid deadlock on oopses, RCU is enough.
  */
 int module_address_lookup(unsigned long addr,
 			  unsigned long *size,
@ include/linux/kallsyms.h:333 @ int module_address_lookup(unsigned long
 	struct module *mod;
 
 	guard(rcu)();
-	preempt_disable();
 	mod = __module_address(addr);
 	if (mod) {
 		if (modname)
@ include/linux/kallsyms.h:350 @ int module_address_lookup(unsigned long
 		if (sym)
 			ret = strscpy(namebuf, sym, KSYM_NAME_LEN);
 	}
-	preempt_enable();
-
 	return ret;
 }
 
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@ include/linux/kallsyms.h:3734 @ const struct exception_table_entry *sear
  */
 bool is_module_address(unsigned long addr)
 {
-	bool ret;
-
-	preempt_disable();
-	ret = __module_address(addr) != NULL;
-	preempt_enable();
-
-	return ret;
+	guard(rcu)();
+	return __module_address(addr) != NULL;
 }
 
 /**