[PATCH] locking/mutex: add MUTEX_WARN_ON to warn invalid mutex

[PATCH] locking/mutex: add MUTEX_WARN_ON to warn invalid mutex

[buckzhang1212]

From: "buck.zhang" <buckzhang1212@yeah.net>

Here is a kernel exception about mutex and I can recreate it stably.
First we define a struct contains a mutex.
Then allocate this struct by kmalloc without calling mutex_init.
Finally when multiple tasks call mutex_lock together,kernel will panic.
This lock is used normally when only one task is using  at a time.
the exception reason is that lock->wait_list is an invalid kernel list.
I want to add more warnings when enable CONFIG_DEBUG_MUTEXES
kernel crash log:
Unable to handle kernel NULL pointer dereference at virtual address 0000000
pc: __mutex_add_waiter+0x68/0x160
lr: __mutex_add_waiter+0x128/0x160
sp: ffffffc0866f3ac0
x29: ffffffc0866f3ad0 x28: ffffff8095148000 x27: 0000000000000000
.............
x2: ffffffc0866f3b18 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
__mutex_add_waiter+0x68/0x160
__mutex_lock+0x48c/0x119c
__mutex_lock_slowpath+0x1c/0x2c
mutex_lock+0x48/0x144
Test case:
struct chip_mutex {
	struct mutex tmutex;
};
static void work_handler1(struct chip_mutex *cmutex)
{
        mutex_lock(&(cmutex->tmutex));
}
static void work_handler2(struct chip_mutex *cmutex)
{
         mutex_lock(&(cmutex->tmutex));
}
static void chip_tmutex(void)
{
	struct chip_mutex *cmutex;
	cmutex = kzalloc(sizeof(struct chip_mutex),GFP_KERNEL);
	work_handler1(cmutex);
	------
	work_handler2(cmutex);
}

Signed-off-by: buck.zhang <buckzhang1212@yeah.net>
---
 kernel/locking/mutex.c |  2 ++
 kernel/locking/mutex.h | 11 +++++++++++
 2 files changed, 13 insertions(+)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index de7d6702c..318d98f2f 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -574,6 +574,8 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
 
 	might_sleep();
 
+	/* In case the mutex is uninitiated, add more warning */
+	MUTEX_WARN_ON(mutex_waitlist_invalid(&lock->wait_list));
 	MUTEX_WARN_ON(lock->magic != lock);
 
 	ww = container_of(lock, struct ww_mutex, base);
diff --git a/kernel/locking/mutex.h b/kernel/locking/mutex.h
index 2e8080a9b..4aaaad10d 100644
--- a/kernel/locking/mutex.h
+++ b/kernel/locking/mutex.h
@@ -48,6 +48,7 @@ static inline struct task_struct *__mutex_owner(struct mutex *lock)
 }
 
 #ifdef CONFIG_DEBUG_MUTEXES
+
 extern void debug_mutex_lock_common(struct mutex *lock,
 				    struct mutex_waiter *waiter);
 extern void debug_mutex_wake_waiter(struct mutex *lock,
@@ -61,6 +62,15 @@ extern void debug_mutex_remove_waiter(struct mutex *lock, struct mutex_waiter *w
 extern void debug_mutex_unlock(struct mutex *lock);
 extern void debug_mutex_init(struct mutex *lock, const char *name,
 			     struct lock_class_key *key);
+
+/*
+ * list_invalid - tests whether mutex-> waitlist  is invalid
+ * @head: the list to test.
+ */
+static inline int mutex_waitlist_invalid(const struct list_head *head)
+{
+	return (unsigned long) READ_ONCE(head->next) < PAGE_OFFSET;
+}
 #else /* CONFIG_DEBUG_MUTEXES */
 # define debug_mutex_lock_common(lock, waiter)		do { } while (0)
 # define debug_mutex_wake_waiter(lock, waiter)		do { } while (0)
@@ -69,5 +79,6 @@ extern void debug_mutex_init(struct mutex *lock, const char *name,
 # define debug_mutex_remove_waiter(lock, waiter, ti)	do { } while (0)
 # define debug_mutex_unlock(lock)			do { } while (0)
 # define debug_mutex_init(lock, name, key)		do { } while (0)
+# define mutex_waitlist_invalid()			do { } while (0)
 #endif /* !CONFIG_DEBUG_MUTEXES */
 #endif /* CONFIG_PREEMPT_RT */
-- 
2.17.1

Re: [PATCH] locking/mutex: add MUTEX_WARN_ON to warn invalid mutex

[Waiman Long]

On 9/27/25 4:00 AM, buckzhang1212@yeah.net wrote:
> From: "buck.zhang" <buckzhang1212@yeah.net>
>
> Here is a kernel exception about mutex and I can recreate it stably.
> First we define a struct contains a mutex.
> Then allocate this struct by kmalloc without calling mutex_init.
> Finally when multiple tasks call mutex_lock together,kernel will panic.
> This lock is used normally when only one task is using  at a time.
> the exception reason is that lock->wait_list is an invalid kernel list.
> I want to add more warnings when enable CONFIG_DEBUG_MUTEXES
> kernel crash log:
> Unable to handle kernel NULL pointer dereference at virtual address 0000000
> pc: __mutex_add_waiter+0x68/0x160
> lr: __mutex_add_waiter+0x128/0x160
> sp: ffffffc0866f3ac0
> x29: ffffffc0866f3ad0 x28: ffffff8095148000 x27: 0000000000000000
> .............
> x2: ffffffc0866f3b18 x1 : 0000000000000000 x0 : 0000000000000000
> Call trace:
> __mutex_add_waiter+0x68/0x160
> __mutex_lock+0x48c/0x119c
> __mutex_lock_slowpath+0x1c/0x2c
> mutex_lock+0x48/0x144
> Test case:
> struct chip_mutex {
> 	struct mutex tmutex;
> };
> static void work_handler1(struct chip_mutex *cmutex)
> {
>          mutex_lock(&(cmutex->tmutex));
> }
> static void work_handler2(struct chip_mutex *cmutex)
> {
>           mutex_lock(&(cmutex->tmutex));
> }
> static void chip_tmutex(void)
> {
> 	struct chip_mutex *cmutex;
> 	cmutex = kzalloc(sizeof(struct chip_mutex),GFP_KERNEL);
> 	work_handler1(cmutex);
> 	------
> 	work_handler2(cmutex);
> }
>
> Signed-off-by: buck.zhang <buckzhang1212@yeah.net>
> ---
>   kernel/locking/mutex.c |  2 ++
>   kernel/locking/mutex.h | 11 +++++++++++
>   2 files changed, 13 insertions(+)
>
> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> index de7d6702c..318d98f2f 100644
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -574,6 +574,8 @@ __mutex_lock_common(struct mutex *lock, unsigned int state, unsigned int subclas
>   
>   	might_sleep();
>   
> +	/* In case the mutex is uninitiated, add more warning */
> +	MUTEX_WARN_ON(mutex_waitlist_invalid(&lock->wait_list));
>   	MUTEX_WARN_ON(lock->magic != lock);

By enabling CONFIG_DEBUG_MUTEXES, the lock->magic check should have 
uncovered the case of mutex_lock() call without mutex initialization. 
The extra wait_list check is likely not necessary.

Cheers,
Longman

Re: [PATCH] locking/mutex: add MUTEX_WARN_ON to warn invalid mutex

[Waiman Long]

On 9/28/25 12:24 PM, buckzhang1212 wrote:
> Hey Long
> you are right,lock->magic check can  help me to get what I want .
> It's a bit late for me, and I want to get the  warning when I first 
> use  the invalid mutex.
> Can I move the lock->magic check to  the mutex_lock?

All the mutex_lock*() functions will eventually call 
__mutex_lock_common() or __mutex_trylock_fast() which also has the check 
. There is no need to duplicate the check in each of them.

Cheers,
Longman