Re: FAILED: patch "[PATCH] PCI: hv: Add pci_destroy_slot() in" failed to apply to 4.14-stable tree

[Sasha Levin <sashal@kernel.org>]

On Wed, May 15, 2019 at 11:20:45PM +0000, Dexuan Cui wrote:
>> From: gregkh@linuxfoundation.org <gregkh@linuxfoundation.org>
>> Sent: Wednesday, May 15, 2019 1:36 AM
>> To: Dexuan Cui <decui@microsoft.com>; lorenzo.pieralisi@arm.com; Michael
>> Kelley <mikelley@microsoft.com>; stephen@networkplumber.org
>> Cc: stable@vger.kernel.org
>> Subject: FAILED: patch "[PATCH] PCI: hv: Add pci_destroy_slot() in" failed to
>> apply to 4.14-stable tree
>>
>>
>> The patch below does not apply to the 4.14-stable tree.
>> If someone wants it applied there, or to any other stable or longterm
>> tree, then please email the backport, including the original git commit
>> id to <stable@vger.kernel.org>.
>>
>> thanks,
>>
>> greg k-h
>>
>> ------------------ original commit in Linus's tree ------------------
>>
>> From 340d455699400f2c2c0f9b3f703ade3085cdb501 Mon Sep 17 00:00:00
>> 2001
>> From: Dexuan Cui <decui@microsoft.com>
>> Date: Mon, 4 Mar 2019 21:34:49 +0000
>> Subject: [PATCH] PCI: hv: Add pci_destroy_slot() in
>>  pci_devices_present_work(), if necessary
>>
>> When we hot-remove a device, usually the host sends us a PCI_EJECT message,
>> and a PCI_BUS_RELATIONS message with bus_rel->device_count == 0.
>>
>> When we execute the quick hot-add/hot-remove test, the host may not send
>> us the PCI_EJECT message if the guest has not fully finished the
>> initialization by sending the PCI_RESOURCES_ASSIGNED* message to the
>> host, so it's potentially unsafe to only depend on the
>> pci_destroy_slot() in hv_eject_device_work() because the code path
>>
>> create_root_hv_pci_bus()
>>  -> hv_pci_assign_slots()
>>
>> is not called in this case. Note: in this case, the host still sends the
>> guest a PCI_BUS_RELATIONS message with bus_rel->device_count == 0.
>>
>> In the quick hot-add/hot-remove test, we can have such a race before
>> the code path
>>
>> pci_devices_present_work()
>>  -> new_pcichild_device()
>>
>> adds the new device into the hbus->children list, we may have already
>> received the PCI_EJECT message, and since the tasklet handler
>>
>> hv_pci_onchannelcallback()
>>
>> may fail to find the "hpdev" by calling
>>
>> get_pcichild_wslot(hbus, dev_message->wslot.slot)
>>
>> hv_pci_eject_device() is not called; Later, by continuing execution
>>
>> create_root_hv_pci_bus()
>>  -> hv_pci_assign_slots()
>>
>> creates the slot and the PCI_BUS_RELATIONS message with
>> bus_rel->device_count == 0 removes the device from hbus->children, and
>> we end up being unable to remove the slot in
>>
>> hv_pci_remove()
>>  -> hv_pci_remove_slots()
>>
>> Remove the slot in pci_devices_present_work() when the device
>> is removed to address this race.
>>
>> pci_devices_present_work() and hv_eject_device_work() run in the
>> singled-threaded hbus->wq, so there is not a double-remove issue for the
>> slot.
>>
>> We cannot offload hv_pci_eject_device() from hv_pci_onchannelcallback()
>> to the workqueue, because we need the hv_pci_onchannelcallback()
>> synchronously call hv_pci_eject_device() to poll the channel
>> ringbuffer to work around the "hangs in hv_compose_msi_msg()" issue
>> fixed in commit de0aa7b2f97d ("PCI: hv: Fix 2 hang issues in
>> hv_compose_msi_msg()")
>>
>> Fixes: a15f2c08c708 ("PCI: hv: support reporting serial number as slot
>> information")
>> Signed-off-by: Dexuan Cui <decui@microsoft.com>
>> [lorenzo.pieralisi@arm.com: rewritten commit log]
>> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
>> Reviewed-by: Stephen Hemminger <stephen@networkplumber.org>
>> Reviewed-by:  Michael Kelley <mikelley@microsoft.com>
>> Cc: stable@vger.kernel.org
>>
>> diff --git a/drivers/pci/controller/pci-hyperv.c
>> b/drivers/pci/controller/pci-hyperv.c
>> index b489412e3502..82acd6155adf 100644
>> --- a/drivers/pci/controller/pci-hyperv.c
>> +++ b/drivers/pci/controller/pci-hyperv.c
>> @@ -1776,6 +1776,10 @@ static void pci_devices_present_work(struct
>> work_struct *work)
>>  		hpdev = list_first_entry(&removed, struct hv_pci_dev,
>>  					 list_entry);
>>  		list_del(&hpdev->list_entry);
>> +
>> +		if (hpdev->pci_slot)
>> +			pci_destroy_slot(hpdev->pci_slot);
>> +
>>  		put_pcichild(hpdev);
>>  	}
>>
>
>Hi,
>I backported the patch for linux-4.14.y.
>
>Please use the attached patch, which is [PATCH 3/3]
>
>Thanks,
>-- Dexuan

Queued for 4.14, thank you.

--
Thanks,
Sasha