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Date:   Tue, 27 Sep 2016 14:29:35 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Long Li <longli@...hange.microsoft.com>
Cc:     "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        devel@...uxdriverproject.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Long Li <longli@...rosoft.com>
Subject: Re: [PATCH 1/2 v2] pci-hyperv: properly handle pci bus remove

On Wed, Sep 14, 2016 at 07:10:01PM -0700, Long Li wrote:
> From: Long Li <longli@...rosoft.com>
> 
> hv_pci_devices_present is called in hv_pci_remove when we remove a PCI device from host (e.g. by disabling SRIOV on a device). In hv_pci_remove, the bus is already removed before the call, so we don't need to rescan the bus in the workqueue scheduled from hv_pci_devices_present. By introducing status hv_pcibus_removed, we can avoid this situation.
> 
> The patch fixes the following kernel panic.
> 
> [  383.853124] Workqueue: events pci_devices_present_work [pci_hyperv]
> [  383.853124] task: ffff88007f5f8000 ti: ffff88007f600000 task.ti:
> ffff88007f600000
> [  383.853124] RIP: 0010:[<ffffffff81349806>]  [<ffffffff81349806>]
> pci_is_pcie+0x6/0x20
> [  383.853124] RSP: 0018:ffff88007f603d38  EFLAGS: 00010206
> [  383.853124] RAX: ffff88007f5f8000 RBX: 642f3d4854415056 RCX:
> ffff88007f603fd8
> [  383.853124] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
> 642f3d4854415056
> [  383.853124] RBP: ffff88007f603d68 R08: 0000000000000246 R09:
> ffffffffa045eb9e
> [  383.853124] R10: ffff88007b419a80 R11: ffffea0001c0ef40 R12:
> ffff880003ee1c00
> [  383.853124] R13: 63702f30303a3137 R14: 0000000000000000 R15:
> 0000000000000246
> [  383.853124] FS:  0000000000000000(0000) GS:ffff88007b400000(0000)
> knlGS:0000000000000000
> [  383.853124] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [  383.853124] CR2: 00007f68b3f52350 CR3: 0000000003546000 CR4:
> 00000000000406f0
> [  383.853124] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
> 0000000000000000
> [  383.853124] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7:
> 0000000000000400
> [  383.853124] Stack:
> [  383.853124]  ffff88007f603d68 ffffffff8134db17 0000000000000008
> ffff880003ee1c00
> [  383.853124]  63702f30303a3137 ffff880003d8edb8 ffff88007f603da0
> ffffffff8134ee2d
> [  383.853124]  ffff880003d8ed00 ffff88007f603dd8 ffff880075fec320
> ffff880003d8edb8
> [  383.853124] Call Trace:
> [  383.853124]  [<ffffffff8134db17>] ? pci_scan_slot+0x27/0x140
> [  383.853124]  [<ffffffff8134ee2d>] pci_scan_child_bus+0x3d/0x150
> [  383.853124]  [<ffffffffa045ef5a>]
> pci_devices_present_work+0x3ea/0x400 [pci_hyperv]
> [  383.853124]  [<ffffffff810a682b>] process_one_work+0x17b/0x470
> [  383.853124]  [<ffffffff810a7666>] worker_thread+0x126/0x410
> [  383.853124]  [<ffffffff810a7540>] ? rescuer_thread+0x460/0x460
> [  383.853124]  [<ffffffff810aee1f>] kthread+0xcf/0xe0
> [  383.853124]  [<ffffffff810aed50>] ?
> kthread_create_on_node+0x140/0x140
> [  383.853124]  [<ffffffff81699958>] ret_from_fork+0x58/0x90
> [  383.853124]  [<ffffffff810aed50>] ?
> kthread_create_on_node+0x140/0x140
> [  383.853124] Code: 89 e5 5d 25 f0 00 00 00 c1 f8 04 c3 66 0f 1f 84 00
> 00 00 00 00 66 66 66 66 90 55 0f b6 47 4a 48 89 e5 5d c3 90 66 66 66 66
> 90 55 <80> 7f 4a 00 48 89 e5 5d 0f 95 c0 c3 0f 1f 40 00 66 2e 0f 1f 84
> [  383.853124] RIP  [<ffffffff81349806>] pci_is_pcie+0x6/0x20
> [  383.853124]  RSP <ffff88007f603d38>

Personally, I would remove the timestamps and addresses from this trace
because I don't think they contribute to diagnosing the problem.

> Signed-off-by: Long Li <longli@...rosoft.com>

I'm ready to apply these but am waiting for an ack from the maintainers
listed in MAINTAINERS (feel free to update that if it's out of date).

> ---
>  drivers/pci/host/pci-hyperv.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/pci/host/pci-hyperv.c b/drivers/pci/host/pci-hyperv.c
> index a8deeca..4a37598 100644
> --- a/drivers/pci/host/pci-hyperv.c
> +++ b/drivers/pci/host/pci-hyperv.c
> @@ -348,6 +348,7 @@ enum hv_pcibus_state {
>  	hv_pcibus_init = 0,
>  	hv_pcibus_probed,
>  	hv_pcibus_installed,
> +	hv_pcibus_removed,
>  	hv_pcibus_maximum
>  };
>  
> @@ -1481,13 +1482,24 @@ static void pci_devices_present_work(struct work_struct *work)
>  		put_pcichild(hpdev, hv_pcidev_ref_initial);
>  	}
>  
> -	/* Tell the core to rescan bus because there may have been changes. */
> -	if (hbus->state == hv_pcibus_installed) {
> +	switch (hbus->state) {
> +	case hv_pcibus_installed:
> +		/*
> +		 * Tell the core to rescan bus
> +		 * because there may have been changes.
> +		 */
>  		pci_lock_rescan_remove();
>  		pci_scan_child_bus(hbus->pci_bus);
>  		pci_unlock_rescan_remove();
> -	} else {
> +		break;
> +
> +	case hv_pcibus_init:
> +	case hv_pcibus_probed:
>  		survey_child_resources(hbus);
> +		break;
> +
> +	default:
> +		break;
>  	}
>  
>  	up(&hbus->enum_sem);
> @@ -2163,6 +2175,7 @@ static int hv_pci_probe(struct hv_device *hdev,
>  	hbus = kzalloc(sizeof(*hbus), GFP_KERNEL);
>  	if (!hbus)
>  		return -ENOMEM;
> +	hbus->state = hv_pcibus_init;
>  
>  	/*
>  	 * The PCI bus "domain" is what is called "segment" in ACPI and
> @@ -2305,6 +2318,7 @@ static int hv_pci_remove(struct hv_device *hdev)
>  		pci_stop_root_bus(hbus->pci_bus);
>  		pci_remove_root_bus(hbus->pci_bus);
>  		pci_unlock_rescan_remove();
> +		hbus->state = hv_pcibus_removed;
>  	}
>  
>  	ret = hv_send_resources_released(hdev);
> -- 
> 1.8.5.6
> 
> --
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