[PATCH 5.10 116/243] PCI: hv: Fix a race condition when removing the device

Greg Kroah-Hartman
2021-07-19T17:17:28Z

From: Long Li <longli@microsoft.com>

[ Upstream commit 94d22763207ac6633612b8d8e0ca4fba0f7aa139 ]

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/destroying the workqueue of hbus before doing hbus remove.

Link: https://lore.kernel.org/r/1620806800-30983-1-git-send-email-longli@linuxonhyperv.com
Signed-off-by: Long Li <longli@microsoft.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/pci/controller/pci-hyperv.c | 30 ++++++++++++++++++++++-------
1 file changed, 23 insertions(+), 7 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index d57c538bbb2d..44e15f0e3a2e 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
};

@@ -3247,8 +3246,9 @@ static int hv_pci_bus_exit(struct hv_device *hdev, bool keep_devs)
struct pci_packet teardown_packet;
u8 buffer[sizeof(struct pci_message)];
} pkt;
- struct hv_dr_state *dr;
struct hv_pci_compl comp_pkt;
+ struct hv_pci_dev *hpdev, *tmp;
+ unsigned long flags;
int ret;

/*
@@ -3260,9 +3260,16 @@ static int hv_pci_bus_exit(struct hv_device *hdev, bool keep_devs)

if (!keep_devs) {
/* Delete any children which might still exist. */
- dr = kzalloc(sizeof(*dr), GFP_KERNEL);
- if (dr && hv_pci_start_relations_work(hbus, dr))
- kfree(dr);
+ spin_lock_irqsave(&hbus->device_list_lock, flags);
+ list_for_each_entry_safe(hpdev, tmp, &hbus->children, list_entry) {
+ list_del(&hpdev->list_entry);
+ if (hpdev->pci_slot)
+ pci_destroy_slot(hpdev->pci_slot);
+ /* For the two refs got in new_pcichild_device() */
+ put_pcichild(hpdev);
+ put_pcichild(hpdev);
+ }
+ spin_unlock_irqrestore(&hbus->device_list_lock, flags);
}

ret = hv_send_resources_released(hdev);
@@ -3305,13 +3312,23 @@ 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);
+ hbus->wq = NULL;
+ /*
+ * 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 +3343,6 @@ 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);

--
2.30.2