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
