From: Michael Kelley (EOSG) Sent: Saturday, March 3, 2018 08:10
From: linux-kernel-owner@vger.kernel.org <linux-kernel-
owner@vger.kernel.org> On Behalf Of Dexuan Cui
Sent: Friday, March 2, 2018 4:21 PM When we hot-remove the device, we first receive a PCI_EJECT message and then receive a PCI_BUS_RELATIONS message with bus_rel->device_count ==
The first message is offloaded to hv_eject_device_work(), and the second is offloaded to pci_devices_present_work(). Both the paths can be running list_del(&hpdev->list_entry), causing general protection fault, because system_wq can run them concurrently.
The patch eliminates the race condition.
With this patch, the enum_sem field in struct hv_pcibus_device is no longer needed. The semaphore serializes execution in hv_pci_devices_present_work(), and that serialization is now done with the ordered workqueue. Also, the last paragraph of the top level comment for hv_pci_devices_present_work() should be updated to reflect the new ordering assumptions.
Thanks! I'll make an extra patch for this.
Separately, an unrelated bug: At the top of hv_eject_device_work(), the first test may do a put_pcichild() and return. This exit path also needs to do put_hvpcibus() to balance the ref counts, or do a goto the last two lines at the bottom of the function.
When we're in hv_eject_device_work(), IMO hpdev->state must be hv_pcichild_ejecting, so I'm going to make a patch like this:
@@ -1867,10 +1867,7 @@ static void hv_eject_device_work(struct work_struct *work)
hpdev = container_of(work, struct hv_pci_dev, wrk);
- if (hpdev->state != hv_pcichild_ejecting) { - put_pcichild(hpdev, hv_pcidev_ref_pnp); - return; - } + WARN_ON(hpdev->state != hv_pcichild_ejecting);
/* * Ejection can come before or after the PCI bus has been set up, so
@@ -1770,7 +1772,7 @@ static void hv_pci_devices_present(struct
hv_pcibus_device *hbus,
spin_unlock_irqrestore(&hbus->device_list_lock, flags);
get_hvpcibus(hbus);
- schedule_work(&dr_wrk->wrk);
- queue_work(hbus->wq, &dr_wrk->wrk);
This invocation of get_hvpcibus() and queue_work() could be made conditional on whether the preceding list_add_tail() transitioned the list from empty to non-empty. If the list was already non-empty, a previously queued invocation of hv_pci_devices_present_work() will find the new entry and process it. But this is an optimization in a non-perf sensitive code path, so may not be worth it.
Exactly. I'll add the the optimization.
@@ -1848,7 +1850,7 @@ static void hv_pci_eject_device(struct hv_pci_dev
*hpdev)
get_pcichild(hpdev, hv_pcidev_ref_pnp); INIT_WORK(&hpdev->wrk, hv_eject_device_work); get_hvpcibus(hpdev->hbus);
- schedule_work(&hpdev->wrk);
- queue_work(hpdev->hbus->wq, &hpdev->wrk);
}
/** @@ -2463,11 +2465,17 @@ static int hv_pci_probe(struct hv_device *hdev, spin_lock_init(&hbus->retarget_msi_interrupt_lock); sema_init(&hbus->enum_sem, 1); init_completion(&hbus->remove_event);
hbus->wq = alloc_ordered_workqueue("hv_pci_%x", 0,
hbus->sysdata.domain);if (!hbus->wq) {
ret = -ENOMEM;goto free_bus;}
ret = vmbus_open(hdev->channel, pci_ring_size, pci_ring_size, NULL, 0, hv_pci_onchannelcallback, hbus); if (ret)
goto free_bus;
goto destroy_wq;hv_set_drvdata(hdev, hbus);
@@ -2536,6 +2544,9 @@ static int hv_pci_probe(struct hv_device *hdev, hv_free_config_window(hbus); close: vmbus_close(hdev->channel); +destroy_wq:
- drain_workqueue(hbus->wq);
The drain_workqueue() call isn't necessary. destroy_workqueue() calls drain_workqueue() and there better not be anything in the workqueue anyway since all the ref counts are zero.
OK. Will remove it.
- destroy_workqueue(hbus->wq);
free_bus: free_page((unsigned long)hbus); return ret; @@ -2615,6 +2626,8 @@ 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);
- drain_workqueue(hbus->wq);
Same here -- drain_workqueue() isn't needed. The workqueue must be empty anyway since the remove_event has completed and the ref counts will all be zero.
Will remove it.
- destroy_workqueue(hbus->wq);
I'm going to post a v2 patchset tomorrow.
Thanks, -- Dexuan