linux-kernel - Re: [tip:sched/core] sched/numa: Move task_numa_free() to __put_task

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Date:	Mon, 14 Apr 2014 02:23:16 +0530 (IST)
From:	Govindarajulu Varadarajan <gvaradar@...co.com>
To:	Mike Galbraith <bitbucket@...ine.de>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Sasha Levin <sasha.levin@...cle.com>, mingo@...nel.org,
	hpa@...or.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, mgorman@...e.com,
	akpm@...ux-foundation.org, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org, Dave Jones <davej@...hat.com>
Subject: Re: [tip:sched/core] sched/numa: Move task_numa_free() to
 __put_task_struct()



On Mon, 7 Apr 2014, Mike Galbraith wrote:

> On Mon, 2014-04-07 at 10:16 +0200, Peter Zijlstra wrote:
>> On Mon, Apr 07, 2014 at 09:30:30AM +0200, Mike Galbraith wrote:
>>> -	double_lock(&my_grp->lock, &grp->lock);
>>> +	BUG_ON(irqs_disabled());
>>> +	double_lock_irq(&my_grp->lock, &grp->lock);
>>
>> So either make this:
>>
>> 	local_irq_disable();
>> 	double_lock();
>>
>> or
>>
>>>
>>>  	for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
>>>  		my_grp->faults[i] -= p->numa_faults_memory[i];
>>> @@ -1692,6 +1693,7 @@ static void task_numa_group(struct task_
>>>
>>>  	spin_unlock(&my_grp->lock);
>>>  	spin_unlock(&grp->lock);
>>> +	local_irq_enable();
>>
>> use:
>> 	spin_unlock()
>> 	spin_unlock_irq()
>>
>> or so, but this imbalance is making my itch :-)
>
> sched, numa: fix task_numa_free() lockdep splat
>
> Sasha reports that lockdep claims 156654f491dd8d52687a5fbe1637f472a52ce75b made
> numa_group.lock interrupt unsafe.  While I don't see how that could be given the
> commit in question moved task_numa_free() from one irq enabled region to another,
> the below does make both gripes and lockups upon gripe with numa=fake=4 go away.
>

Hi

I Am hitting this bug quite frequently. I do not see the problem after applying
this patch.

Thanks

Tested-by: Govindarajulu Varadarajan <govindx7c6@...il.com>

> Reported-by: Sasha Levin <sasha.levin@...cle.com>
> Signed-off-by: Mike Galbraith <bitbucket@...ine.de>
> ---
> kernel/sched/fair.c  |   13 +++++++------
> kernel/sched/sched.h |    9 +++++++++
> 2 files changed, 16 insertions(+), 6 deletions(-)
>
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1497,7 +1497,7 @@ static void task_numa_placement(struct t
> 	/* If the task is part of a group prevent parallel updates to group stats */
> 	if (p->numa_group) {
> 		group_lock = &p->numa_group->lock;
> -		spin_lock(group_lock);
> +		spin_lock_irq(group_lock);
> 	}
>
> 	/* Find the node with the highest number of faults */
> @@ -1572,7 +1572,7 @@ static void task_numa_placement(struct t
> 			}
> 		}
>
> -		spin_unlock(group_lock);
> +		spin_unlock_irq(group_lock);
> 	}
>
> 	/* Preferred node as the node with the most faults */
> @@ -1677,7 +1677,8 @@ static void task_numa_group(struct task_
> 	if (!join)
> 		return;
>
> -	double_lock(&my_grp->lock, &grp->lock);
> +	BUG_ON(irqs_disabled());
> +	double_lock_irq(&my_grp->lock, &grp->lock);
>
> 	for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++) {
> 		my_grp->faults[i] -= p->numa_faults_memory[i];
> @@ -1691,7 +1692,7 @@ static void task_numa_group(struct task_
> 	grp->nr_tasks++;
>
> 	spin_unlock(&my_grp->lock);
> -	spin_unlock(&grp->lock);
> +	spin_unlock_irq(&grp->lock);
>
> 	rcu_assign_pointer(p->numa_group, grp);
>
> @@ -1710,14 +1711,14 @@ void task_numa_free(struct task_struct *
> 	void *numa_faults = p->numa_faults_memory;
>
> 	if (grp) {
> -		spin_lock(&grp->lock);
> +		spin_lock_irq(&grp->lock);
> 		for (i = 0; i < NR_NUMA_HINT_FAULT_STATS * nr_node_ids; i++)
> 			grp->faults[i] -= p->numa_faults_memory[i];
> 		grp->total_faults -= p->total_numa_faults;
>
> 		list_del(&p->numa_entry);
> 		grp->nr_tasks--;
> -		spin_unlock(&grp->lock);
> +		spin_unlock_irq(&grp->lock);
> 		rcu_assign_pointer(p->numa_group, NULL);
> 		put_numa_group(grp);
> 	}
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1388,6 +1388,15 @@ static inline void double_lock(spinlock_
> 	spin_lock_nested(l2, SINGLE_DEPTH_NESTING);
> }
>
> +static inline void double_lock_irq(spinlock_t *l1, spinlock_t *l2)
> +{
> +	if (l1 > l2)
> +		swap(l1, l2);
> +
> +	spin_lock_irq(l1);
> +	spin_lock_nested(l2, SINGLE_DEPTH_NESTING);
> +}
> +
> static inline void double_raw_lock(raw_spinlock_t *l1, raw_spinlock_t *l2)
> {
> 	if (l1 > l2)
>
>
> --
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