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Commit c797384e authored by Suren Baghdasaryan's avatar Suren Baghdasaryan
Browse files

ANDROID: kthread: break dependency between worker->lock and task_struct->pi_lock 

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: default avatarKe Wang <ke.wang@unisoc.com>
Reported-by: default avatarShakeel Butt <shakeelb@google.com>
Suggested-by: default avatarPeter Zijlstra <peterz@infradead.org>
Tested-by: default avatarShakeel Butt <shakeelb@google.com>
Signed-off-by: default avatarSuren Baghdasaryan <surenb@google.com>

Link: https://lkml.org/lkml/2020/5/4/1148


Cherry picked instead of commit 461daba06bdcb9c7a3f92b9bbd110e1f7d093ffc
as an alternative solution for the lockdep error that does not break KMI.
Bug: 174875976
Signed-off-by: default avatarSuren Baghdasaryan <surenb@google.com>
Change-Id: I2478847f66c85dca953846cd77955928d690c97c
parent 9c7cbdf8

kernel/kthread.c

+33 −11
Original line number Diff line number Diff line
@@ -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;
@@ -897,7 +907,7 @@ 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;

	}
@@ -930,17 +940,21 @@ 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);
@@ -969,6 +983,7 @@ 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;
@@ -981,15 +996,18 @@ 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);

}
@@ -1067,6 +1085,7 @@ 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;
@@ -1085,9 +1104,12 @@ 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);