Re: [Patch v1 0/7] mpt3sas: Hot-Plug Surprise removal support on IOC.

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On Tue, Sep 04, 2018 at 11:19:04AM +0530, Sreekanth Reddy wrote:
> On Fri, Aug 31, 2018 at 2:25 PM, Lukas Wunner <lukas@xxxxxxxxx> wrote:
> > * Just reading the vendor ID may not be sufficient to detect unplug,
> >   it may also read as "all ones" if the link is down due to error
> >   recovery by DPC.
> 
> So, is their any other way to detect pci device unplug apart from
> reading the vendor ID, I mean we have check any other flags, etc?

Many scsi drivers call pci_channel_offline() to detect inaccessibility
of the device due to a PCI error:
https://elixir.bootlin.com/linux/v4.19-rc2/ident/pci_channel_offline

A patch is pending such that surprise removal can also be queried
with that same function:
https://www.spinics.net/lists/linux-pci/msg75722.html


> > * I don't see why you need to poll for the device's removal from a
> >   watchdog thread.  pciehp will invoke your driver's ->remove hook
> >   once the device is gone.
> 
> If we have some three to four PCI devices and all pci devices are hot
> unplugged simultaneously, then we observed that driver's-remove hook
> is called sequentially. So it takes some time to call fourth PCI
> device driver's->remove hook. so during this time we want all the
> outstanding commands to be gracefully terminated and hence we added
> this watchdog thread to quickly detect the hba unplug and take
> necessary steps such as gracefully terminate the outstanding IOs and
> stop receiving further IOs on it. At later time when PCI subsystem
> calls driver's-remove hook then driver can quickly release the
> resources allocated for this unplugged device.

pciehp does the following as soon as the surprise removal event is handled:

	pci_dev_set_disconnected(dev, NULL);
	if (pci_has_subordinate(dev))
		pci_walk_bus(dev->subordinate, pci_dev_set_disconnected, NULL);

Thus, once the above-linked patch lands, you'll be able to detect
surprise removal by calling pci_channel_offline() or checking
pdev->error_state == pci_channel_io_perm_failure, obviating the
need to poll for surprise removal from a kthread.

There's another patch pending to move pci_walk_bus() out of the
pci_lock_rescan_remove() so that it runs even earlier, without
pointlessly waiting for a lock:
https://www.spinics.net/lists/linux-pci/msg75438.html

Thanks,

Lukas



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