linux-kernel - [PATCH v2 14/28] module: Use RCU in all users of __module

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Message-ID: <20241220174731.514432-15-bigeasy@linutronix.de>
Date: Fri, 20 Dec 2024 18:41:28 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-modules@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Daniel Gomez <da.gomez@...sung.com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Petr Pavlu <petr.pavlu@...e.com>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH v2 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.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 include/linux/kallsyms.h | 3 +--
 kernel/module/kallsyms.c | 5 +----
 kernel/module/main.c     | 9 ++-------
 3 files changed, 4 insertions(+), 13 deletions(-)

diff --git a/include/linux/kallsyms.h b/include/linux/kallsyms.h
index 1c6a6c1704d8d..d5dd54c53ace6 100644
--- a/include/linux/kallsyms.h
+++ b/include/linux/kallsyms.h
@@ -55,12 +55,11 @@ static inline void *dereference_symbol_descriptor(void *ptr)
 	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;
 }
diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c
index 0e8ec6486d95c..00a60796327c0 100644
--- a/kernel/module/kallsyms.c
+++ b/kernel/module/kallsyms.c
@@ -316,7 +316,7 @@ void * __weak dereference_module_function_descriptor(struct module *mod,
 
 /*
  * 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,
@@ -330,7 +330,6 @@ int module_address_lookup(unsigned long addr,
 	struct module *mod;
 
 	guard(rcu)();
-	preempt_disable();
 	mod = __module_address(addr);
 	if (mod) {
 		if (modname)
@@ -348,8 +347,6 @@ int module_address_lookup(unsigned long addr,
 		if (sym)
 			ret = strscpy(namebuf, sym, KSYM_NAME_LEN);
 	}
-	preempt_enable();
-
 	return ret;
 }
 
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 74b9e9ddb4b65..80877741ac7e5 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -3649,13 +3649,8 @@ const struct exception_table_entry *search_module_extables(unsigned long addr)
  */
 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;
 }
 
 /**
-- 
2.45.2