| Message ID | 20180303001947.20564-2-decui@microsoft.com (mailing list archive) |
|---|---|
| State | New, archived |
| Delegated to: | Bjorn Helgaas |
| Headers | show |
> -----Original Message----- > 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 > To: bhelgaas@google.com; linux-pci@vger.kernel.org; KY Srinivasan <kys@microsoft.com>; > Stephen Hemminger <sthemmin@microsoft.com> > Cc: linux-kernel@vger.kernel.org; driverdev-devel@linuxdriverproject.org; Haiyang Zhang > <haiyangz@microsoft.com>; olaf@aepfle.de; apw@canonical.com; jasowang@redhat.com; > vkuznets@redhat.com; marcelo.cerri@canonical.com; Dexuan Cui <decui@microsoft.com>; > Jack Morgenstein <jackm@mellanox.com>; stable@vger.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@microsoft.com> > Tested-by: Adrian Suhov <v-adsuho@microsoft.com> > Tested-by: Chris Valean <v-chvale@microsoft.com> > Cc: Vitaly Kuznetsov <vkuznets@redhat.com> > Cc: Jack Morgenstein <jackm@mellanox.com> > Cc: stable@vger.kernel.org > Cc: Stephen Hemminger <sthemmin@microsoft.com> > Cc: K. Y. Srinivasan <kys@microsoft.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
> 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 == > 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. 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
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); } /** @@ -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); + 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); + destroy_workqueue(hbus->wq); free_page((unsigned long)hbus); return 0; }