linux-kernel - Re: [RFC PATCH 1/2] PCI: correctly flush workqueue when destroy pcie hotplug controller

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Message-ID: <CAErSpo7qqDJ+pM-OZN6wDRGCU3duLd1-hjA5_LA+em=PBVuY0Q@mail.gmail.com>
Date:	Wed, 25 Apr 2012 11:23:20 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
Cc:	Jiang Liu <liuj97@...il.com>, Yinghai Lu <yinghai@...nel.org>,
	Jiang Liu <jiang.liu@...wei.com>,
	matsumoto.hiroo@...fujitsu.com,
	Keping Chen <chenkeping@...wei.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] PCI: correctly flush workqueue when destroy pcie
 hotplug controller

On Tue, Apr 10, 2012 at 4:43 AM, Kenji Kaneshige
<kaneshige.kenji@...fujitsu.com> wrote:
> I think you're rignt.
>
> Reviewed-by: Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
>
> (2012/04/08 3:18), Jiang Liu wrote:
>> When destroying a PCIe hotplug controller, all work items associated with
>> that controller should be flushed.  Function pcie_cleanup_slot() calls
>> cancel_delayed_work() and flush_workqueue() to achieve that.
>> Function flush_workqueue() will flush all work items already submitted,
>> but new work items submitted by those already submitted work items may
>> still be in live state when returning from flush_workqueue().
>>
>> For the extreme case, pciehp driver may expierence following calling path:
>> 1) pcie_isr() ->  pciehp_handle_xxx() ->  queue_interrupt_event()->queue_work()
>> 2) interrupt_event_handler() ->  handle_button_press_event() ->
>>     queue_delayed_work()
>> 3) pciehp_queue_pushbutton_work() ->  queue_work()
>>
>> So enhance pcie_cleanup_slot() to correctly flush workqueue when destroying
>> PCIe hotplug controller.
>>
>> Signed-off-by: Jiang Liu<jiang.liu@...wei.com>
>> ---
>>   drivers/pci/hotplug/pciehp_hpc.c |   13 ++++++++++++-
>>   1 files changed, 12 insertions(+), 1 deletions(-)
>>
>> diff --git a/drivers/pci/hotplug/pciehp_hpc.c b/drivers/pci/hotplug/pciehp_hpc.c
>> index d4fa705..9a48a51 100644
>> --- a/drivers/pci/hotplug/pciehp_hpc.c
>> +++ b/drivers/pci/hotplug/pciehp_hpc.c
>> @@ -890,8 +890,19 @@ static int pcie_init_slot(struct controller *ctrl)
>>   static void pcie_cleanup_slot(struct controller *ctrl)
>>   {
>>       struct slot *slot = ctrl->slot;
>> -     cancel_delayed_work(&slot->work);
>> +
>> +     /*
>> +      * Following workqueue flushing logic is to deal with the special call path:
>> +      * 1) pcie_isr() ->  pciehp_handle_xxx() ->
>> +      *    queue_interrupt_event(pciehp_wq_event)->queue_work(pciehp_wq)
>> +      * 2) interrupt_event_handler() ->  handle_button_press_event() ->
>> +      *    queue_delayed_work(pciehp_wq)
>> +      * 3) pciehp_queue_pushbutton_work() ->  queue_work(pciehp_wq)
>> +      */
>>       flush_workqueue(pciehp_wq);
>> +     cancel_delayed_work_sync(&slot->work);
>> +     flush_workqueue(pciehp_wq);
>> +
>>       kfree(slot);
>>   }

Jiang, I'm ignoring this (and the next [2/2] patch) because I assume
they're superceded by the "[PATCH RFC 00/17] Introduce a global lock
to serialize all PCI hotplug" series of April 16.  Let me know if
otherwise.

Bjorn
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