Messages in this thread Patch in this message | | | Date | Mon, 4 May 2020 11:25:40 -0700 | Subject | [PATCH v2 1/1] kthread: break dependency between worker->lock and task_struct->pi_lock | From | Suren Baghdasaryan <> |
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A number of kthread-related functions indirectly take task_struct->pi_lock while holding worker->lock in the call chain like this: spin_lock(&worker->lock) kthread_insert_work wake_up_process try_to_wake_up raw_spin_lock_irqsave(&p->pi_lock, flags)
This lock dependency exists whenever kthread_insert_work is called either directly or indirectly via __kthread_queue_delayed_work in the following functions: kthread_queue_work kthread_delayed_work_timer_fn kthread_queue_delayed_work kthread_flush_work kthread_mod_delayed_work
This creates possibilities for circular dependencies like the one reported at [1]. Break this lock dependency by moving task wakeup after worker->lock has been released.
[1]: https://lore.kernel.org/lkml/CAJuCfpG4NkhpQvZjgXZ_3gm6Hf1QgN_eUOQ8iX9Cv1k9whLwSQ@mail.gmail.com
Reported-by: Ke Wang <ke.wang@unisoc.com> Reported-by: Shakeel Butt <shakeelb@google.com> Suggested-by: Peter Zijlstra <peterz@infradead.org> Tested-by: Shakeel Butt <shakeelb@google.com> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
--- v2: * replace lkml link with lore.kernel.org one * change a line break to be more consistent with the rest of the code --- kernel/kthread.c | 44 +++++++++++++++++++++++++++++++++----------- 1 file changed, 33 insertions(+), 11 deletions(-)
diff --git a/kernel/kthread.c b/kernel/kthread.c index bfbfa481be3a..d37cd37d934c 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -9,6 +9,7 @@ #include <uapi/linux/sched/types.h> #include <linux/sched.h> #include <linux/sched/task.h> +#include <linux/sched/wake_q.h> #include <linux/kthread.h> #include <linux/completion.h> #include <linux/err.h> @@ -806,14 +807,15 @@ static void kthread_insert_work_sanity_check(struct kthread_worker *worker, /* insert @work before @pos in @worker */ static void kthread_insert_work(struct kthread_worker *worker, struct kthread_work *work, - struct list_head *pos) + struct list_head *pos, + struct wake_q_head *wake_q) { kthread_insert_work_sanity_check(worker, work); list_add_tail(&work->node, pos); work->worker = worker; if (!worker->current_work && likely(worker->task)) - wake_up_process(worker->task); + wake_q_add(wake_q, worker->task); } /** @@ -831,15 +833,19 @@ static void kthread_insert_work(struct kthread_worker *worker, bool kthread_queue_work(struct kthread_worker *worker, struct kthread_work *work) { - bool ret = false; + DEFINE_WAKE_Q(wake_q); unsigned long flags; + bool ret = false; raw_spin_lock_irqsave(&worker->lock, flags); if (!queuing_blocked(worker, work)) { - kthread_insert_work(worker, work, &worker->work_list); + kthread_insert_work(worker, work, &worker->work_list, &wake_q); ret = true; } raw_spin_unlock_irqrestore(&worker->lock, flags); + + wake_up_q(&wake_q); + return ret; } EXPORT_SYMBOL_GPL(kthread_queue_work); @@ -857,6 +863,7 @@ void kthread_delayed_work_timer_fn(struct timer_list *t) struct kthread_delayed_work *dwork = from_timer(dwork, t, timer); struct kthread_work *work = &dwork->work; struct kthread_worker *worker = work->worker; + DEFINE_WAKE_Q(wake_q); unsigned long flags; /* @@ -873,15 +880,18 @@ void kthread_delayed_work_timer_fn(struct timer_list *t) /* Move the work from worker->delayed_work_list. */ WARN_ON_ONCE(list_empty(&work->node)); list_del_init(&work->node); - kthread_insert_work(worker, work, &worker->work_list); + kthread_insert_work(worker, work, &worker->work_list, &wake_q); raw_spin_unlock_irqrestore(&worker->lock, flags); + + wake_up_q(&wake_q); } EXPORT_SYMBOL(kthread_delayed_work_timer_fn); static void __kthread_queue_delayed_work(struct kthread_worker *worker, struct kthread_delayed_work *dwork, - unsigned long delay) + unsigned long delay, + struct wake_q_head *wake_q) { struct timer_list *timer = &dwork->timer; struct kthread_work *work = &dwork->work; @@ -895,7 +905,7 @@ static void __kthread_queue_delayed_work(struct kthread_worker *worker, * on that there's no such delay when @delay is 0. */ if (!delay) { - kthread_insert_work(worker, work, &worker->work_list); + kthread_insert_work(worker, work, &worker->work_list, wake_q); return; } @@ -928,17 +938,21 @@ bool kthread_queue_delayed_work(struct kthread_worker *worker, unsigned long delay) { struct kthread_work *work = &dwork->work; + DEFINE_WAKE_Q(wake_q); unsigned long flags; bool ret = false; raw_spin_lock_irqsave(&worker->lock, flags); if (!queuing_blocked(worker, work)) { - __kthread_queue_delayed_work(worker, dwork, delay); + __kthread_queue_delayed_work(worker, dwork, delay, &wake_q); ret = true; } raw_spin_unlock_irqrestore(&worker->lock, flags); + + wake_up_q(&wake_q); + return ret; } EXPORT_SYMBOL_GPL(kthread_queue_delayed_work); @@ -967,6 +981,7 @@ void kthread_flush_work(struct kthread_work *work) KTHREAD_WORK_INIT(fwork.work, kthread_flush_work_fn), COMPLETION_INITIALIZER_ONSTACK(fwork.done), }; + DEFINE_WAKE_Q(wake_q); struct kthread_worker *worker; bool noop = false; @@ -979,15 +994,18 @@ void kthread_flush_work(struct kthread_work *work) WARN_ON_ONCE(work->worker != worker); if (!list_empty(&work->node)) - kthread_insert_work(worker, &fwork.work, work->node.next); + kthread_insert_work(worker, &fwork.work, + work->node.next, &wake_q); else if (worker->current_work == work) kthread_insert_work(worker, &fwork.work, - worker->work_list.next); + worker->work_list.next, &wake_q); else noop = true; raw_spin_unlock_irq(&worker->lock); + wake_up_q(&wake_q); + if (!noop) wait_for_completion(&fwork.done); } @@ -1065,6 +1083,7 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker, unsigned long delay) { struct kthread_work *work = &dwork->work; + DEFINE_WAKE_Q(wake_q); unsigned long flags; int ret = false; @@ -1083,9 +1102,12 @@ bool kthread_mod_delayed_work(struct kthread_worker *worker, ret = __kthread_cancel_work(work, true, &flags); fast_queue: - __kthread_queue_delayed_work(worker, dwork, delay); + __kthread_queue_delayed_work(worker, dwork, delay, &wake_q); out: raw_spin_unlock_irqrestore(&worker->lock, flags); + + wake_up_q(&wake_q); + return ret; } EXPORT_SYMBOL_GPL(kthread_mod_delayed_work); -- 2.26.2.526.g744177e7f7-goog
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