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Date:   Thu, 24 May 2018 09:35:57 -0400
From:   okaya@codeaurora.org
To:     Bjorn Helgaas <helgaas@kernel.org>
Cc:     linux-pci@vger.kernel.org, timur@codeaurora.org, ryan@finnie.org,
        linux-arm-msm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org, stable@vger.kernel.org,
        Bjorn Helgaas <bhelgaas@google.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Frederick Lawler <fred@fredlawl.com>,
        Dongdong Liu <liudongdong3@huawei.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        open list <linux-kernel@vger.kernel.org>,
        Don Brace <don.brace@microsemi.com>,
        esc.storagedev@microsemi.com, linux-scsi@vger.kernel.org
Subject: Re: [PATCH V2] PCI/portdrv: do not disable device on reboot/shutdown
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On 2018-05-24 09:07, Bjorn Helgaas wrote:
> On Thu, May 24, 2018 at 07:43:05AM -0400, Sinan Kaya wrote:
>> On 5/23/2018 6:57 PM, Sinan Kaya wrote:
>> >> The crash seems to indicate that the hpsa device attempted a DMA after
>> >> we cleared the Root Port's PCI_COMMAND_MASTER, which means
>> >> hpsa_shutdown() didn't stop DMA from the device (it looks like *most*
>> >> shutdown methods don't disable device DMA, so it's in good company).
>> > All drivers are expected to shutdown DMA and interrupts in their shutdown()
>> > routines. They can skip removing threads, data structures etc. but DMA and
>> > interrupt disabling are required. This is the difference between shutdown()
>> > and remove() callbacks.
>> 
>> I found this note yesterday to see why we are not disabling the
>> devices in the PCI core itself.
>> 
>> pci_device_remove()
>> 
>> 	/*
>> 	 * We would love to complain here if pci_dev->is_enabled is set, that
>> 	 * the driver should have called pci_disable_device(), but the
>> 	 * unfortunate fact is there are too many odd BIOS and bridge setups
>> 	 * that don't like drivers doing that all of the time.
>> 	 * Oh well, we can dream of sane hardware when we sleep, no matter 
>> how
>> 	 * horrible the crap we have to deal with is when we are awake...
>> 	 */
>> 
>> Ryan, can you discard the previous patch and test this one instead?
>> remove() path in hpsa driver seems to call pci_disable_device() via
>> 
>> hpsa_remove_one()
>> 	hpsa_free_pci_init()
>> 
>> but nothing on the shutdown path.
>> 
>> diff --git a/drivers/scsi/hpsa.c b/drivers/scsi/hpsa.c
>> index 4ed3d26..3823f04 100644
>> --- a/drivers/scsi/hpsa.c
>> +++ b/drivers/scsi/hpsa.c
>> @@ -8651,6 +8651,7 @@ static void hpsa_shutdown(struct pci_dev *pdev)
>>         h->access.set_intr_mask(h, HPSA_INTR_OFF);
>>         hpsa_free_irqs(h);                      /* init_one 4 */
>>         hpsa_disable_interrupt_mode(h);         /* pci_init 2 */
>> +       pci_disable_device(h->pdev);
>>  }
> 
> I suspect this will make things "work" (if the device can't attempt
> DMA, no Unsupported Request error will occur).
> 
> But I'm concerned that the reason for the DMA might that hpsa is
> transferring buffers from system memory to the hpsa device, and if we
> arbitrarily terminate those transfers with pci_disable_device(), we
> may leave the hpsa device in an inconsistent state, e.g., with a dirty
> filesystem.
> 
> But we really need guidance from an hpsa expert.  I don't know the
> filesystem/SCSI/hpsa details.

Agreed,

We can drop shutdown and use the remove callback. Remove is supposed to 
do a safe cleanup.

> 
> Bjorn