From 2333e829952fb437db915bbb17f4d8c43127d438 Mon Sep 17 00:00:00 2001 From: Yu Chen Date: Sun, 23 Feb 2020 15:28:52 +0800 Subject: workqueue: Make workqueue_init*() return void The return values of workqueue_init() and workqueue_early_int() are always 0, and there is no usage of their return value. So just make them return void. Signed-off-by: Yu Chen Signed-off-by: Tejun Heo --- kernel/workqueue.c | 8 ++------ 1 file changed, 2 insertions(+), 6 deletions(-) (limited to 'kernel/workqueue.c') diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 301db4406bc3..5afa9ad45eba 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -5896,7 +5896,7 @@ static void __init wq_numa_init(void) * items. Actual work item execution starts only after kthreads can be * created and scheduled right before early initcalls. */ -int __init workqueue_init_early(void) +void __init workqueue_init_early(void) { int std_nice[NR_STD_WORKER_POOLS] = { 0, HIGHPRI_NICE_LEVEL }; int hk_flags = HK_FLAG_DOMAIN | HK_FLAG_WQ; @@ -5963,8 +5963,6 @@ int __init workqueue_init_early(void) !system_unbound_wq || !system_freezable_wq || !system_power_efficient_wq || !system_freezable_power_efficient_wq); - - return 0; } /** @@ -5976,7 +5974,7 @@ int __init workqueue_init_early(void) * are no kworkers executing the work items yet. Populate the worker pools * with the initial workers and enable future kworker creations. */ -int __init workqueue_init(void) +void __init workqueue_init(void) { struct workqueue_struct *wq; struct worker_pool *pool; @@ -6023,6 +6021,4 @@ int __init workqueue_init(void) wq_online = true; wq_watchdog_init(); - - return 0; } -- cgit v1.2.3 From 00d5d15b0641f4ae463253eba06c836d56c2ce42 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Tue, 10 Mar 2020 16:23:19 +0000 Subject: workqueue: Mark up unlocked access to wq->first_flusher [ 7329.671518] BUG: KCSAN: data-race in flush_workqueue / flush_workqueue [ 7329.671549] [ 7329.671572] write to 0xffff8881f65fb250 of 8 bytes by task 37173 on cpu 2: [ 7329.671607] flush_workqueue+0x3bc/0x9b0 (kernel/workqueue.c:2844) [ 7329.672527] [ 7329.672540] read to 0xffff8881f65fb250 of 8 bytes by task 37175 on cpu 0: [ 7329.672571] flush_workqueue+0x28d/0x9b0 (kernel/workqueue.c:2835) Signed-off-by: Chris Wilson Cc: Tejun Heo Cc: Lai Jiangshan Signed-off-by: Tejun Heo --- kernel/workqueue.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'kernel/workqueue.c') diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 5afa9ad45eba..40a4ba39ad5e 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2832,7 +2832,7 @@ void flush_workqueue(struct workqueue_struct *wq) * First flushers are responsible for cascading flushes and * handling overflow. Non-first flushers can simply return. */ - if (wq->first_flusher != &this_flusher) + if (READ_ONCE(wq->first_flusher) != &this_flusher) return; mutex_lock(&wq->mutex); @@ -2841,7 +2841,7 @@ void flush_workqueue(struct workqueue_struct *wq) if (wq->first_flusher != &this_flusher) goto out_unlock; - wq->first_flusher = NULL; + WRITE_ONCE(wq->first_flusher, NULL); WARN_ON_ONCE(!list_empty(&this_flusher.list)); WARN_ON_ONCE(wq->flush_color != this_flusher.flush_color); -- cgit v1.2.3 From 62849a9612924a655c67cf6962920544aa5c20db Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Sat, 28 Mar 2020 00:29:59 +0100 Subject: workqueue: Remove the warning in wq_worker_sleeping() The kernel test robot triggered a warning with the following race: task-ctx A interrupt-ctx B worker -> process_one_work() -> work_item() -> schedule(); -> sched_submit_work() -> wq_worker_sleeping() -> ->sleeping = 1 atomic_dec_and_test(nr_running) __schedule(); *interrupt* async_page_fault() -> local_irq_enable(); -> schedule(); -> sched_submit_work() -> wq_worker_sleeping() -> if (WARN_ON(->sleeping)) return -> __schedule() -> sched_update_worker() -> wq_worker_running() -> atomic_inc(nr_running); -> ->sleeping = 0; -> sched_update_worker() -> wq_worker_running() if (!->sleeping) return In this context the warning is pointless everything is fine. An interrupt before wq_worker_sleeping() will perform the ->sleeping assignment (0 -> 1 > 0) twice. An interrupt after wq_worker_sleeping() will trigger the warning and nr_running will be decremented (by A) and incremented once (only by B, A will skip it). This is the case until the ->sleeping is zeroed again in wq_worker_running(). Remove the WARN statement because this condition may happen. Document that preemption around wq_worker_sleeping() needs to be disabled to protect ->sleeping and not just as an optimisation. Fixes: 6d25be5782e48 ("sched/core, workqueues: Distangle worker accounting from rq lock") Reported-by: kernel test robot Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Cc: Tejun Heo Link: https://lkml.kernel.org/r/20200327074308.GY11705@shao2-debian --- kernel/sched/core.c | 3 ++- kernel/workqueue.c | 6 ++++-- 2 files changed, 6 insertions(+), 3 deletions(-) (limited to 'kernel/workqueue.c') diff --git a/kernel/sched/core.c b/kernel/sched/core.c index f6b329bca0c6..c3d12e3762d4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4120,7 +4120,8 @@ static inline void sched_submit_work(struct task_struct *tsk) * it wants to wake up a task to maintain concurrency. * As this function is called inside the schedule() context, * we disable preemption to avoid it calling schedule() again - * in the possible wakeup of a kworker. + * in the possible wakeup of a kworker and because wq_worker_sleeping() + * requires it. */ if (tsk->flags & (PF_WQ_WORKER | PF_IO_WORKER)) { preempt_disable(); diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 3816a18c251e..891ccad5f271 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -858,7 +858,8 @@ void wq_worker_running(struct task_struct *task) * @task: task going to sleep * * This function is called from schedule() when a busy worker is - * going to sleep. + * going to sleep. Preemption needs to be disabled to protect ->sleeping + * assignment. */ void wq_worker_sleeping(struct task_struct *task) { @@ -875,7 +876,8 @@ void wq_worker_sleeping(struct task_struct *task) pool = worker->pool; - if (WARN_ON_ONCE(worker->sleeping)) + /* Return if preempted before wq_worker_running() was reached */ + if (worker->sleeping) return; worker->sleeping = 1; -- cgit v1.2.3