From 265f3ed077036f053981f5eea0b5b43e7c5b39ff Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Sun, 24 Sep 2023 17:07:02 +0200 Subject: workqueue: Provide one lock class key per work_on_cpu() callsite All callers of work_on_cpu() share the same lock class key for all the functions queued. As a result the workqueue related locking scenario for a function A may be spuriously accounted as an inversion against the locking scenario of function B such as in the following model: long A(void *arg) { mutex_lock(&mutex); mutex_unlock(&mutex); } long B(void *arg) { } void launchA(void) { work_on_cpu(0, A, NULL); } void launchB(void) { mutex_lock(&mutex); work_on_cpu(1, B, NULL); mutex_unlock(&mutex); } launchA and launchB running concurrently have no chance to deadlock. However the above can be reported by lockdep as a possible locking inversion because the works containing A() and B() are treated as belonging to the same locking class. The following shows an existing example of such a spurious lockdep splat: ====================================================== WARNING: possible circular locking dependency detected 6.6.0-rc1-00065-g934ebd6e5359 #35409 Not tainted ------------------------------------------------------ kworker/0:1/9 is trying to acquire lock: ffffffff9bc72f30 (cpu_hotplug_lock){++++}-{0:0}, at: _cpu_down+0x57/0x2b0 but task is already holding lock: ffff9e3bc0057e60 ((work_completion)(&wfc.work)){+.+.}-{0:0}, at: process_scheduled_works+0x216/0x500 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 ((work_completion)(&wfc.work)){+.+.}-{0:0}: __flush_work+0x83/0x4e0 work_on_cpu+0x97/0xc0 rcu_nocb_cpu_offload+0x62/0xb0 rcu_nocb_toggle+0xd0/0x1d0 kthread+0xe6/0x120 ret_from_fork+0x2f/0x40 ret_from_fork_asm+0x1b/0x30 -> #1 (rcu_state.barrier_mutex){+.+.}-{3:3}: __mutex_lock+0x81/0xc80 rcu_nocb_cpu_deoffload+0x38/0xb0 rcu_nocb_toggle+0x144/0x1d0 kthread+0xe6/0x120 ret_from_fork+0x2f/0x40 ret_from_fork_asm+0x1b/0x30 -> #0 (cpu_hotplug_lock){++++}-{0:0}: __lock_acquire+0x1538/0x2500 lock_acquire+0xbf/0x2a0 percpu_down_write+0x31/0x200 _cpu_down+0x57/0x2b0 __cpu_down_maps_locked+0x10/0x20 work_for_cpu_fn+0x15/0x20 process_scheduled_works+0x2a7/0x500 worker_thread+0x173/0x330 kthread+0xe6/0x120 ret_from_fork+0x2f/0x40 ret_from_fork_asm+0x1b/0x30 other info that might help us debug this: Chain exists of: cpu_hotplug_lock --> rcu_state.barrier_mutex --> (work_completion)(&wfc.work) Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock((work_completion)(&wfc.work)); lock(rcu_state.barrier_mutex); lock((work_completion)(&wfc.work)); lock(cpu_hotplug_lock); *** DEADLOCK *** 2 locks held by kworker/0:1/9: #0: ffff900481068b38 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x212/0x500 #1: ffff9e3bc0057e60 ((work_completion)(&wfc.work)){+.+.}-{0:0}, at: process_scheduled_works+0x216/0x500 stack backtrace: CPU: 0 PID: 9 Comm: kworker/0:1 Not tainted 6.6.0-rc1-00065-g934ebd6e5359 #35409 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 Workqueue: events work_for_cpu_fn Call Trace: rcu-torture: rcu_torture_read_exit: Start of episode dump_stack_lvl+0x4a/0x80 check_noncircular+0x132/0x150 __lock_acquire+0x1538/0x2500 lock_acquire+0xbf/0x2a0 ? _cpu_down+0x57/0x2b0 percpu_down_write+0x31/0x200 ? _cpu_down+0x57/0x2b0 _cpu_down+0x57/0x2b0 __cpu_down_maps_locked+0x10/0x20 work_for_cpu_fn+0x15/0x20 process_scheduled_works+0x2a7/0x500 worker_thread+0x173/0x330 ? __pfx_worker_thread+0x10/0x10 kthread+0xe6/0x120 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x2f/0x40 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1b/0x30 Signed-off-by: Frederic Weisbecker Signed-off-by: Tejun Heo --- include/linux/workqueue.h | 46 +++++++++++++++++++++++++++++++++++++++------- 1 file changed, 39 insertions(+), 7 deletions(-) (limited to 'include/linux/workqueue.h') diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h index 1c1d06804d45..24b1e5070f4d 100644 --- a/include/linux/workqueue.h +++ b/include/linux/workqueue.h @@ -274,18 +274,16 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; } * to generate better code. */ #ifdef CONFIG_LOCKDEP -#define __INIT_WORK(_work, _func, _onstack) \ +#define __INIT_WORK_KEY(_work, _func, _onstack, _key) \ do { \ - static struct lock_class_key __key; \ - \ __init_work((_work), _onstack); \ (_work)->data = (atomic_long_t) WORK_DATA_INIT(); \ - lockdep_init_map(&(_work)->lockdep_map, "(work_completion)"#_work, &__key, 0); \ + lockdep_init_map(&(_work)->lockdep_map, "(work_completion)"#_work, (_key), 0); \ INIT_LIST_HEAD(&(_work)->entry); \ (_work)->func = (_func); \ } while (0) #else -#define __INIT_WORK(_work, _func, _onstack) \ +#define __INIT_WORK_KEY(_work, _func, _onstack, _key) \ do { \ __init_work((_work), _onstack); \ (_work)->data = (atomic_long_t) WORK_DATA_INIT(); \ @@ -294,12 +292,22 @@ static inline unsigned int work_static(struct work_struct *work) { return 0; } } while (0) #endif +#define __INIT_WORK(_work, _func, _onstack) \ + do { \ + static __maybe_unused struct lock_class_key __key; \ + \ + __INIT_WORK_KEY(_work, _func, _onstack, &__key); \ + } while (0) + #define INIT_WORK(_work, _func) \ __INIT_WORK((_work), (_func), 0) #define INIT_WORK_ONSTACK(_work, _func) \ __INIT_WORK((_work), (_func), 1) +#define INIT_WORK_ONSTACK_KEY(_work, _func, _key) \ + __INIT_WORK_KEY((_work), (_func), 1, _key) + #define __INIT_DELAYED_WORK(_work, _func, _tflags) \ do { \ INIT_WORK(&(_work)->work, (_func)); \ @@ -693,8 +701,32 @@ static inline long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg) return fn(arg); } #else -long work_on_cpu(int cpu, long (*fn)(void *), void *arg); -long work_on_cpu_safe(int cpu, long (*fn)(void *), void *arg); +long work_on_cpu_key(int cpu, long (*fn)(void *), + void *arg, struct lock_class_key *key); +/* + * A new key is defined for each caller to make sure the work + * associated with the function doesn't share its locking class. + */ +#define work_on_cpu(_cpu, _fn, _arg) \ +({ \ + static struct lock_class_key __key; \ + \ + work_on_cpu_key(_cpu, _fn, _arg, &__key); \ +}) + +long work_on_cpu_safe_key(int cpu, long (*fn)(void *), + void *arg, struct lock_class_key *key); + +/* + * A new key is defined for each caller to make sure the work + * associated with the function doesn't share its locking class. + */ +#define work_on_cpu_safe(_cpu, _fn, _arg) \ +({ \ + static struct lock_class_key __key; \ + \ + work_on_cpu_safe_key(_cpu, _fn, _arg, &__key); \ +}) #endif /* CONFIG_SMP */ #ifdef CONFIG_FREEZER -- cgit