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([2601:188:c180:4250:ecbe:130d:668d:951d]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-793472c3946sm100462706d6.28.2025.09.23.20.10.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 23 Sep 2025 20:10:23 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: Date: Tue, 23 Sep 2025 23:10:22 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] locking/mutex:add MUTEX_CHCEK_INIT to detect uninitialized mutex lock To: buckzhang1212@yeah.net, Peter Zijlstra , Ingo Molnar , Will Deacon , Boqun Feng , linux-kernel@vger.kernel.org References: <20250924022500.2577-1-buckzhang1212@yeah.net> Content-Language: en-US In-Reply-To: <20250924022500.2577-1-buckzhang1212@yeah.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 9/23/25 10:25 PM, buckzhang1212@yeah.net wrote: > From: "buck.zhang" > > 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 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;