> -----Original Message-----
> From: Dexuan Cui <decui@xxxxxxxxxxxxx>
> Sent: Tuesday, March 28, 2023 10:21 AM
> To: bhelgaas@xxxxxxxxxx; davem@xxxxxxxxxxxxx; Dexuan Cui
> <decui@xxxxxxxxxxxxx>; edumazet@xxxxxxxxxx; Haiyang Zhang
> <haiyangz@xxxxxxxxxxxxx>; Jake Oshins <jakeo@xxxxxxxxxxxxx>;
> kuba@xxxxxxxxxx; kw@xxxxxxxxx; KY Srinivasan <kys@xxxxxxxxxxxxx>;
> leon@xxxxxxxxxx; linux-pci@xxxxxxxxxxxxxxx; lpieralisi@xxxxxxxxxx; Michael
> Kelley (LINUX) <mikelley@xxxxxxxxxxxxx>; pabeni@xxxxxxxxxx;
> robh@xxxxxxxxxx; saeedm@xxxxxxxxxx; wei.liu@xxxxxxxxxx; Long Li
> <longli@xxxxxxxxxxxxx>; boqun.feng@xxxxxxxxx
> Cc: linux-hyperv@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux-
> rdma@xxxxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx
> Subject: [EXTERNAL] [PATCH 1/6] PCI: hv: fix a race condition bug in
> hv_pci_query_relations()
>
> Fix the longstanding race between hv_pci_query_relations() and
> survey_child_resources() by flushing the workqueue before we exit from
> hv_pci_query_relations().
>
> Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft
> Hyper-V VMs")
> Signed-off-by: Dexuan Cui <decui@xxxxxxxxxxxxx>
>
> ---
> drivers/pci/controller/pci-hyperv.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> With the below debug code:
>
> @@ -2103,6 +2103,8 @@ static void survey_child_resources(struct
> hv_pcibus_device *hbus)
> }
>
> spin_unlock_irqrestore(&hbus->device_list_lock, flags);
> + ssleep(15);
> + printk("%s: completing %px\n", __func__, event);
> complete(event);
> }
>
> @@ -3305,8 +3307,12 @@ static int hv_pci_query_relations(struct hv_device
> *hdev)
>
> ret = vmbus_sendpacket(hdev->channel, &message, sizeof(message),
> 0, VM_PKT_DATA_INBAND, 0);
> - if (!ret)
> + if (!ret) {
> + ssleep(10); // unassign the PCI device on the host during the
> 10s
> ret = wait_for_response(hdev, &comp);
> + printk("%s: comp=%px is becoming invalid! ret=%d\n",
> + __func__, &comp, ret);
> + }
>
> return ret;
> }
> @@ -3635,6 +3641,8 @@ static int hv_pci_probe(struct hv_device *hdev,
>
> retry:
> ret = hv_pci_query_relations(hdev);
> + printk("hv_pci_query_relations() exited\n");
Can we use pr_* or the appropriate KERN_<LEVEL> in all the printk(s).
> +
> if (ret)
> goto free_irq_domain;
>
> I'm able to repro the below hang issue:
>
> [ 74.544744] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: PCI VMBus
> probing: Using version 0x10004
> [ 76.886944] hv_netvsc 818fe754-b912-4445-af51-1f584812e3c9 eth0: VF slot
> 1 removed
> [ 84.788266] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: The device is
> gone.
> [ 84.792586] hv_pci_query_relations: comp=ffffa7504012fb58 is becoming
> invalid! ret=-19
> [ 84.797505] hv_pci_query_relations() exited
> [ 89.652268] survey_child_resources: completing ffffa7504012fb58
> [ 150.392242] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
> [ 150.398447] rcu: 15-...0: (2 ticks this GP)
> idle=867c/1/0x4000000000000000 softirq=947/947 fqs=5234
> [ 150.405851] rcu: (detected by 14, t=15004 jiffies, g=2553, q=4833
> ncpus=16)
> [ 150.410870] Sending NMI from CPU 14 to CPUs 15:
> [ 150.414836] NMI backtrace for cpu 15
> [ 150.414840] CPU: 15 PID: 10 Comm: kworker/u32:0 Tainted: G W E
> 6.3.0-rc3-decui-dirty #34
> ...
> [ 150.414849] Workqueue: hv_pci_468b pci_devices_present_work
> [pci_hyperv] [ 150.414866] RIP:
> 0010:__pv_queued_spin_lock_slowpath+0x10f/0x3c0
> ...
> [ 150.414905] Call Trace:
> [ 150.414907] <TASK>
> [ 150.414911] _raw_spin_lock_irqsave+0x40/0x50 [ 150.414917]
> complete+0x1d/0x60 [ 150.414924] pci_devices_present_work+0x5dd/0x680
> [pci_hyperv] [ 150.414946] process_one_work+0x21f/0x430 [ 150.414952]
> worker_thread+0x4a/0x3c0
>
> With this patch, the hang issue goes away:
>
> [ 186.143612] hv_pci b92a0085-468b-407a-a88a-d33fac8edc75: The device is
> gone.
> [ 186.148034] hv_pci_query_relations: comp=ffffa7cfd0aa3b50 is becoming
> invalid! ret=-19 [ 191.263611] survey_child_resources: completing
> ffffa7cfd0aa3b50 [ 191.267732] hv_pci_query_relations() exited
>
> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-
> hyperv.c
> index f33370b75628..b82c7cde19e6 100644
> --- a/drivers/pci/controller/pci-hyperv.c
> +++ b/drivers/pci/controller/pci-hyperv.c
> @@ -3308,6 +3308,19 @@ static int hv_pci_query_relations(struct hv_device
> *hdev)
> if (!ret)
> ret = wait_for_response(hdev, &comp);
>
> + /*
> + * In the case of fast device addition/removal, it's possible that
> + * vmbus_sendpacket() or wait_for_response() returns -ENODEV but
> we
> + * already got a PCI_BUS_RELATIONS* message from the host and the
> + * channel callback already scheduled a work to hbus->wq, which can
> be
> + * running survey_child_resources() -> complete(&hbus-
> >survey_event),
> + * even after hv_pci_query_relations() exits and the stack variable
> + * 'comp' is no longer valid. This can cause a strange hang issue
> + * or sometimes a page fault. Flush hbus->wq before we exit from
> + * hv_pci_query_relations() to avoid the issues.
> + */
> + flush_workqueue(hbus->wq);
> +
> return ret;
> }
>
> --
> 2.25.1
