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Date: Sat, 3 Mar 2018 16:09:46 +0000
From: "Michael Kelley (EOSG)" <Michael.H.Kelley@...rosoft.com>
To: Dexuan Cui <decui@...rosoft.com>,
"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
KY Srinivasan <kys@...rosoft.com>,
Stephen Hemminger <sthemmin@...rosoft.com>
CC: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"driverdev-devel@...uxdriverproject.org"
<driverdev-devel@...uxdriverproject.org>,
Haiyang Zhang <haiyangz@...rosoft.com>,
"olaf@...fle.de" <olaf@...fle.de>,
"apw@...onical.com" <apw@...onical.com>,
"jasowang@...hat.com" <jasowang@...hat.com>,
"vkuznets@...hat.com" <vkuznets@...hat.com>,
"marcelo.cerri@...onical.com" <marcelo.cerri@...onical.com>,
Dexuan Cui <decui@...rosoft.com>,
Jack Morgenstein <jackm@...lanox.com>,
"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH 2/3] PCI: hv: serialize the present/eject work items
> -----Original Message-----
> From: linux-kernel-owner@...r.kernel.org <linux-kernel-owner@...r.kernel.org> On Behalf
> Of Dexuan Cui
> Sent: Friday, March 2, 2018 4:21 PM
> To: bhelgaas@...gle.com; linux-pci@...r.kernel.org; KY Srinivasan <kys@...rosoft.com>;
> Stephen Hemminger <sthemmin@...rosoft.com>
> Cc: linux-kernel@...r.kernel.org; driverdev-devel@...uxdriverproject.org; Haiyang Zhang
> <haiyangz@...rosoft.com>; olaf@...fle.de; apw@...onical.com; jasowang@...hat.com;
> vkuznets@...hat.com; marcelo.cerri@...onical.com; Dexuan Cui <decui@...rosoft.com>;
> Jack Morgenstein <jackm@...lanox.com>; stable@...r.kernel.org
> Subject: [PATCH 2/3] PCI: hv: serialize the present/eject work items
>
> 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 == 0.
>
> 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.
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.
>
> Signed-off-by: Dexuan Cui <decui@...rosoft.com>
> Tested-by: Adrian Suhov <v-adsuho@...rosoft.com>
> Tested-by: Chris Valean <v-chvale@...rosoft.com>
> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
> Cc: Jack Morgenstein <jackm@...lanox.com>
> Cc: stable@...r.kernel.org
> Cc: Stephen Hemminger <sthemmin@...rosoft.com>
> Cc: K. Y. Srinivasan <kys@...rosoft.com>
> ---
> drivers/pci/host/pci-hyperv.c | 19 ++++++++++++++++---
> 1 file changed, 16 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
> index 1233300f41c6..57b1fb3ebdb9 100644
> --- a/drivers/pci/host/pci-hyperv.c
> +++ b/drivers/pci/host/pci-hyperv.c
> @@ -461,6 +461,8 @@ struct hv_pcibus_device {
> struct retarget_msi_interrupt retarget_msi_interrupt_params;
>
> spinlock_t retarget_msi_interrupt_lock;
> +
> + struct workqueue_struct *wq;
> };
>
> /*
> @@ -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.
> }
>
> /**
> @@ -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.
> + 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.
> + destroy_workqueue(hbus->wq);
> free_page((unsigned long)hbus);
> return 0;
> }
> --
> 2.7.4
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