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[PATCH] locking/mutex:add MUTEX_CHCEK_INIT to detect uninitialized mutex lock

buckzhang1212@yeah.net posted 1 patch 4 months, 2 weeks ago 
kernel/locking/mutex.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
[PATCH] locking/mutex:add MUTEX_CHCEK_INIT to detect uninitialized mutex lock
Posted by buckzhang1212@yeah.net 4 months, 2 weeks ago 
From: "buck.zhang" <buckzhang1212@yeah.net>

Here is a kernel exception about mutex and I can recreate it stably.
First we define a custome struct that includes a mutex lock.
Then allocate this struct by kmalloc without calling mutex_init.
Finally when multiple tasks call mutex_lock together,kernel will panic.
But Kernel is good  if only one task call this mutex at the same time.
the exception reason is that lock->wait_list is an invalid kernel list.
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 | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index de7d6702c..8fbe858c8 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -42,6 +42,16 @@
 #else
 # define MUTEX_WARN_ON(cond)
 #endif
+#define MUTEX_CHCEK_INIT(lock)  mutex_check_waitlist(lock)
+static void mutex_check_waitlist(struct mutex *lock)
+{
+	struct list_head *list = &lock->wait_list;
+
+	if ((unsigned long)list->next < PAGE_OFFSET) {
+		pr_err("BUG: mutex lock is uninitialized，wait_list is Error\n");
+		MUTEX_WARN_ON("mutex lock is uninitialized");
+	}
+}
 
 void
 __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
@@ -269,6 +279,7 @@ static void __sched __mutex_lock_slowpath(struct mutex *lock);
 void __sched mutex_lock(struct mutex *lock)
 {
 	might_sleep();
+	MUTEX_CHCEK_INIT(lock);
 
 	if (!__mutex_trylock_fast(lock))
 		__mutex_lock_slowpath(lock);
@@ -991,6 +1002,7 @@ __mutex_lock_interruptible_slowpath(struct mutex *lock);
 int __sched mutex_lock_interruptible(struct mutex *lock)
 {
 	might_sleep();
+	MUTEX_CHCEK_INIT(lock);
 
 	if (__mutex_trylock_fast(lock))
 		return 0;
@@ -1015,6 +1027,7 @@ EXPORT_SYMBOL(mutex_lock_interruptible);
 int __sched mutex_lock_killable(struct mutex *lock)
 {
 	might_sleep();
+	MUTEX_CHCEK_INIT(lock);
 
 	if (__mutex_trylock_fast(lock))
 		return 0;
-- 
2.17.1
Re: [PATCH] locking/mutex:add MUTEX_CHCEK_INIT to detect uninitialized mutex lock
Posted by kernel test robot 4 months, 2 weeks ago 
Hi,

kernel test robot noticed the following build warnings:

[auto build test WARNING on tip/locking/core]
[also build test WARNING on linus/master v6.17-rc7 next-20250923]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/buckzhang1212-yeah-net/locking-mutex-add-MUTEX_CHCEK_INIT-to-detect-uninitialized-mutex-lock/20250924-103805
base:   tip/locking/core
patch link:    https://lore.kernel.org/r/20250924022500.2577-1-buckzhang1212%40yeah.net
patch subject: [PATCH] locking/mutex:add MUTEX_CHCEK_INIT to detect uninitialized mutex lock
config: i386-randconfig-014-20250924 (https://download.01.org/0day-ci/archive/20250924/202509242322.VggjpcD5-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250924/202509242322.VggjpcD5-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202509242322.VggjpcD5-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> kernel/locking/mutex.c:46:13: warning: 'mutex_check_waitlist' defined but not used [-Wunused-function]
      46 | static void mutex_check_waitlist(struct mutex *lock)
         |             ^~~~~~~~~~~~~~~~~~~~


vim +/mutex_check_waitlist +46 kernel/locking/mutex.c

    39	
    40	#ifdef CONFIG_DEBUG_MUTEXES
    41	# define MUTEX_WARN_ON(cond) DEBUG_LOCKS_WARN_ON(cond)
    42	#else
    43	# define MUTEX_WARN_ON(cond)
    44	#endif
    45	#define MUTEX_CHCEK_INIT(lock)  mutex_check_waitlist(lock)
  > 46	static void mutex_check_waitlist(struct mutex *lock)
    47	{
    48		struct list_head *list = &lock->wait_list;
    49	
    50		if ((unsigned long)list->next < PAGE_OFFSET) {
    51			pr_err("BUG: mutex lock is uninitialized，wait_list is Error\n");
    52			MUTEX_WARN_ON("mutex lock is uninitialized");
    53		}
    54	}
    55	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
Re: [PATCH] locking/mutex:add MUTEX_CHCEK_INIT to detect uninitialized mutex lock
Posted by Waiman Long 4 months, 2 weeks ago 
On 9/23/25 10:25 PM, 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 custome struct that includes a mutex lock.
> Then allocate this struct by kmalloc without calling mutex_init.
> Finally when multiple tasks call mutex_lock together,kernel will panic.
> But Kernel is good  if only one task call this mutex at the same time.
> the exception reason is that lock->wait_list is an invalid kernel list.
> 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>
A mutex must be properly initialized before it can be used. The kernel 
panic you listed above is expected and the panic itself indicates that 
the code is wrong.
> ---
>   kernel/locking/mutex.c | 12 ++++++++++++
>   1 file changed, 12 insertions(+)
>
> diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
> index de7d6702c..8fbe858c8 100644
> --- a/kernel/locking/mutex.c
> +++ b/kernel/locking/mutex.c
> @@ -42,6 +42,16 @@
>   #else
>   # define MUTEX_WARN_ON(cond)
>   #endif
> +#define MUTEX_CHCEK_INIT(lock)  mutex_check_waitlist(lock)
> +static void mutex_check_waitlist(struct mutex *lock)
> +{
> +	struct list_head *list = &lock->wait_list;
> +
> +	if ((unsigned long)list->next < PAGE_OFFSET) {
> +		pr_err("BUG: mutex lock is uninitialized，wait_list is Error\n");
> +		MUTEX_WARN_ON("mutex lock is uninitialized");
> +	}
> +}
>   
>   void
>   __mutex_init(struct mutex *lock, const char *name, struct lock_class_key *key)
> @@ -269,6 +279,7 @@ static void __sched __mutex_lock_slowpath(struct mutex *lock);
>   void __sched mutex_lock(struct mutex *lock)
>   {
>   	might_sleep();
> +	MUTEX_CHCEK_INIT(lock);
>   
>   	if (!__mutex_trylock_fast(lock))
>   		__mutex_lock_slowpath(lock);

This check has provided no additional value and it slows down the 
locking fast path.

NACK

> @@ -991,6 +1002,7 @@ __mutex_lock_interruptible_slowpath(struct mutex *lock);
>   int __sched mutex_lock_interruptible(struct mutex *lock)
>   {
>   	might_sleep();
> +	MUTEX_CHCEK_INIT(lock);
>   
>   	if (__mutex_trylock_fast(lock))
>   		return 0;
> @@ -1015,6 +1027,7 @@ EXPORT_SYMBOL(mutex_lock_interruptible);
>   int __sched mutex_lock_killable(struct mutex *lock)
>   {
>   	might_sleep();
> +	MUTEX_CHCEK_INIT(lock);
>   
>   	if (__mutex_trylock_fast(lock))
>   		return 0;
Re: [PATCH] locking/mutex:add MUTEX_CHCEK_INIT to detect uninitialized mutex lock
Posted by Peter Zijlstra 4 months, 2 weeks ago 
On Tue, Sep 23, 2025 at 11:10:22PM -0400, Waiman Long wrote:
> On 9/23/25 10:25 PM, buckzhang1212@yeah.net wrote:

> A mutex must be properly initialized before it can be used. The kernel panic
> you listed above is expected and the panic itself indicates that the code is
> wrong.

> > @@ -269,6 +279,7 @@ static void __sched __mutex_lock_slowpath(struct mutex *lock);
> >   void __sched mutex_lock(struct mutex *lock)
> >   {
> >   	might_sleep();
> > +	MUTEX_CHCEK_INIT(lock);
> >   	if (!__mutex_trylock_fast(lock))
> >   		__mutex_lock_slowpath(lock);
> 
> This check has provided no additional value and it slows down the locking
> fast path.
> 
> NACK

Agreed. Additionally we have CONFIG_DEBUG_MUTEXES. If you feel there is
a check missing there -- you could argue that debug_mutex_lock_common()
should have something like:

  DEBUG_LOCK_WARN_ON(lock->magic != lock);

feel free to send a patch for that.

But don't go sprinkle debug code in !debug builds.

Patchew 2.1-devel-b67e4c2

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