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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] PCI: hv: Fix a race condition when removing the device
Date:   Mon, 19 Apr 2021 12:20:54 -0700
Message-Id: <1618860054-928-1-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>
---
 drivers/pci/controller/pci-hyperv.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 27a17a1e4a7c..116815404313 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -3305,6 +3305,17 @@ 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);
+
+		flush_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);
-- 
2.27.0