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From:   longli@linuxonhyperv.com
To:     "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Rob Herring <robh@kernel.org>,
        Bjorn Helgaas <bhelgaas@google.com>,
        linux-hyperv@vger.kernel.org, linux-pci@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Long Li <longli@microsoft.com>
Subject: [Patch v2 1/2] PCI: hv: Fix a race condition when removing the device
Date:   Wed, 21 Apr 2021 22:45:45 -0700
Message-Id: <1619070346-21557-1-git-send-email-longli@linuxonhyperv.com>
Precedence: bulk

From: Long Li <longli@microsoft.com>

On removing the device, any work item (hv_pci_devices_present() or
hv_pci_eject_device()) scheduled on workqueue hbus->wq may still be running
and race with hv_pci_remove().

This can happen because the host may send PCI_EJECT or PCI_BUS_RELATIONS(2)
and decide to rescind the channel immediately after that.

Fix this by flushing/stopping the workqueue of hbus before doing hbus remove.

Signed-off-by: Long Li <longli@microsoft.com>
---

Change in v2: Remove unused bus state hv_pcibus_removed

 drivers/pci/controller/pci-hyperv.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 27a17a1e4a7c..fc948a2ed703 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -444,7 +444,6 @@ enum hv_pcibus_state {
 	hv_pcibus_probed,
 	hv_pcibus_installed,
 	hv_pcibus_removing,
-	hv_pcibus_removed,
 	hv_pcibus_maximum
 };
 
@@ -3305,13 +3304,22 @@ static int hv_pci_remove(struct hv_device *hdev)
 
 	hbus = hv_get_drvdata(hdev);
 	if (hbus->state == hv_pcibus_installed) {
+		tasklet_disable(&hdev->channel->callback_event);
+		hbus->state = hv_pcibus_removing;
+		tasklet_enable(&hdev->channel->callback_event);
+		destroy_workqueue(hbus->wq);
+		/*
+		 * At this point, no work is running or can be scheduled
+		 * on hbus-wq. We can't race with hv_pci_devices_present()
+		 * or hv_pci_eject_device(), it's safe to proceed.
+		 */
+
 		/* Remove the bus from PCI's point of view. */
 		pci_lock_rescan_remove();
 		pci_stop_root_bus(hbus->pci_bus);
 		hv_pci_remove_slots(hbus);
 		pci_remove_root_bus(hbus->pci_bus);
 		pci_unlock_rescan_remove();
-		hbus->state = hv_pcibus_removed;
 	}
 
 	ret = hv_pci_bus_exit(hdev, false);
@@ -3326,7 +3334,6 @@ static int hv_pci_remove(struct hv_device *hdev)
 	irq_domain_free_fwnode(hbus->sysdata.fwnode);
 	put_hvpcibus(hbus);
 	wait_for_completion(&hbus->remove_event);
-	destroy_workqueue(hbus->wq);
 
 	hv_put_dom_num(hbus->sysdata.domain);
 
-- 
2.27.0