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From: Adrian Hunter <adrian.hunter@intel.com>
To: Tejun Heo <tj@kernel.org>, Peter Zijlstra <peterz@infradead.org>
Cc: Ulrich Obergfell <uobergfe@redhat.com>,
	Ingo Molnar <mingo@redhat.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue
Date: Thu, 10 Mar 2016 17:12:54 +0200	[thread overview]
Message-ID: <56E18EF6.1010006@intel.com> (raw)
In-Reply-To: <20151203192616.GJ27463@mtj.duckdns.org>

On 03/12/15 21:26, Tejun Heo wrote:
> Task or work item involved in memory reclaim trying to flush a
> non-WQ_MEM_RECLAIM workqueue or one of its work items can lead to
> deadlock.  Trigger WARN_ONCE() if such conditions are detected.
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> ---
> Hello,
> 
> So, something like this.  Seems to work fine here.  If there's no
> objection, I'm gonna push it through wq/for-4.5.
> 
> Thanks.
> 
>  kernel/workqueue.c |   35 +++++++++++++++++++++++++++++++++++
>  1 file changed, 35 insertions(+)
> 
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -2330,6 +2330,37 @@ repeat:
>  	goto repeat;
>  }
>  
> +/**
> + * check_flush_dependency - check for flush dependency sanity
> + * @target_wq: workqueue being flushed
> + * @target_work: work item being flushed (NULL for workqueue flushes)
> + *
> + * %current is trying to flush the whole @target_wq or @target_work on it.
> + * If @target_wq doesn't have %WQ_MEM_RECLAIM, verify that %current is not
> + * reclaiming memory or running on a workqueue which doesn't have
> + * %WQ_MEM_RECLAIM as that can break forward-progress guarantee leading to
> + * a deadlock.
> + */
> +static void check_flush_dependency(struct workqueue_struct *target_wq,
> +				   struct work_struct *target_work)
> +{
> +	work_func_t target_func = target_work ? target_work->func : NULL;
> +	struct worker *worker;
> +
> +	if (target_wq->flags & WQ_MEM_RECLAIM)
> +		return;
> +
> +	worker = current_wq_worker();
> +
> +	WARN_ONCE(current->flags & PF_MEMALLOC,
> +		  "workqueue: PF_MEMALLOC task %d(%s) is flushing !WQ_MEM_RECLAIM %s:%pf",
> +		  current->pid, current->comm, target_wq->name, target_func);
> +	WARN_ONCE(worker && (worker->current_pwq->wq->flags & WQ_MEM_RECLAIM),
> +		  "workqueue: WQ_MEM_RECLAIM %s:%pf is flushing !WQ_MEM_RECLAIM %s:%pf",
> +		  worker->current_pwq->wq->name, worker->current_func,
> +		  target_wq->name, target_func);
> +}
> +
>  struct wq_barrier {
>  	struct work_struct	work;
>  	struct completion	done;
> @@ -2539,6 +2570,8 @@ void flush_workqueue(struct workqueue_st
>  		list_add_tail(&this_flusher.list, &wq->flusher_overflow);
>  	}
>  
> +	check_flush_dependency(wq, NULL);
> +
>  	mutex_unlock(&wq->mutex);
>  
>  	wait_for_completion(&this_flusher.done);
> @@ -2711,6 +2744,8 @@ static bool start_flush_work(struct work
>  		pwq = worker->current_pwq;
>  	}
>  
> +	check_flush_dependency(pwq->wq, work);
> +
>  	insert_wq_barrier(pwq, barr, work, worker);
>  	spin_unlock_irq(&pool->lock);
>  
> 

I am hitting the warnings when using cancel_delayed_work_sync().  I would
have thought that forward progress would still be guaranteed in that case.
Is it true that it is not?

  parent reply	other threads:[~2016-03-10 15:16 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-12-03  0:28 [PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Tejun Heo
2015-12-03  0:28 ` [PATCH 2/2] workqueue: implement lockup detector Tejun Heo
2015-12-03 14:49   ` Tejun Heo
2015-12-03 17:50   ` Don Zickus
2015-12-03 19:43     ` Tejun Heo
2015-12-03 20:12       ` Ulrich Obergfell
2015-12-03 20:54         ` Tejun Heo
2015-12-04  8:02           ` Ingo Molnar
2015-12-04 16:52             ` Don Zickus
2015-12-04 13:19           ` Ulrich Obergfell
2015-12-07 19:06   ` [PATCH v2 " Tejun Heo
2015-12-07 21:38     ` Don Zickus
2015-12-07 21:39       ` Tejun Heo
2015-12-08 16:00         ` Don Zickus
2015-12-08 16:31           ` Tejun Heo
2015-12-03  9:33 ` [PATCH 1/2] watchdog: introduce touch_softlockup_watchdog_sched() Peter Zijlstra
2015-12-03 10:00   ` Peter Zijlstra
2015-12-03 14:48     ` Tejun Heo
2015-12-03 15:04       ` Peter Zijlstra
2015-12-03 15:06         ` Tejun Heo
2015-12-03 19:26           ` [PATCH] workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue Tejun Heo
2015-12-03 20:43             ` Peter Zijlstra
2015-12-03 20:56               ` Tejun Heo
2015-12-03 21:09                 ` Peter Zijlstra
2015-12-03 22:04                   ` Tejun Heo
2015-12-04 12:51                     ` Peter Zijlstra
2015-12-07 15:58             ` Tejun Heo
2016-01-26 17:38             ` Thierry Reding
2016-01-28 10:12               ` Peter Zijlstra
2016-01-28 12:47                 ` Thierry Reding
2016-01-28 12:48                   ` Thierry Reding
2016-01-29 11:09                 ` Tejun Heo
2016-01-29 15:17                   ` Peter Zijlstra
2016-01-29 18:28                     ` Tejun Heo
2016-01-29 10:59               ` [PATCH wq/for-4.5-fixes] workqueue: skip flush dependency checks for legacy workqueues Tejun Heo
2016-01-29 15:07                 ` Thierry Reding
2016-01-29 18:32                 ` Tejun Heo
2016-02-02  6:54                 ` Archit Taneja
2016-03-10 15:12             ` Adrian Hunter [this message]
2016-03-11 17:52               ` [PATCH] workqueue: warn if memory reclaim tries to flush !WQ_MEM_RECLAIM workqueue Tejun Heo

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