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

* FAILED: patch "[PATCH] PCI: hv: Add pci_destroy_slot() in" failed to apply to 4.14-stable tree
@ 2019-05-15  8:35 gregkh
  2019-05-15 23:20 ` Dexuan Cui
  0 siblings, 1 reply; 3+ messages in thread
From: gregkh @ 2019-05-15  8:35 UTC (permalink / raw)
  To: decui, lorenzo.pieralisi, mikelley, stephen; +Cc: stable


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);
 	}
 


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