Re: [Patch v3 1/2] PCI: hv: Fix a race condition when removing the device

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

On Wed, May 12, 2021 at 01:06:40AM -0700, longli@linuxonhyperv.com wrote:
> From: Long Li <longli@microsoft.com>
> 
> 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.
> 
> Signed-off-by: Long Li <longli@microsoft.com>
> ---
> Change in v2: Remove unused bus state hv_pcibus_removed
> Change in v3: Change hv_pci_bus_exit() to not use workqueue to remove PCI devices
> 
>  drivers/pci/controller/pci-hyperv.c | 30 ++++++++++++++++++++++-------
>  1 file changed, 23 insertions(+), 7 deletions(-)

Applied series to pci/hv, thanks.

Lorenzo

> diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> index 27a17a1e4a7c..c6122a1b0c46 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);
>  
> -- 
> 2.27.0
>