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    Subject[PATCH -v4] PCI: Make sriov work with hotplug remove

    When hot remove pci express module that have pcie switch and support SRIOV, got

    [ 5918.610127] pciehp 0000:80:02.2:pcie04: pcie_isr: intr_loc 1
    [ 5918.615779] pciehp 0000:80:02.2:pcie04: Attention button interrupt received
    [ 5918.622730] pciehp 0000:80:02.2:pcie04: Button pressed on Slot(3)
    [ 5918.629002] pciehp 0000:80:02.2:pcie04: pciehp_get_power_status: SLOTCTRL a8 value read 1f9
    [ 5918.637416] pciehp 0000:80:02.2:pcie04: PCI slot #3 - powering off due to button press.
    [ 5918.647125] pciehp 0000:80:02.2:pcie04: pcie_isr: intr_loc 10
    [ 5918.653039] pciehp 0000:80:02.2:pcie04: pciehp_green_led_blink: SLOTCTRL a8 write cmd 200
    [ 5918.661229] pciehp 0000:80:02.2:pcie04: pciehp_set_attention_status: SLOTCTRL a8 write cmd c0
    [ 5924.667627] pciehp 0000:80:02.2:pcie04: Disabling domain:bus:device=0000:b0:00
    [ 5924.674909] pciehp 0000:80:02.2:pcie04: pciehp_get_power_status: SLOTCTRL a8 value read 2f9
    [ 5924.683262] pciehp 0000:80:02.2:pcie04: pciehp_unconfigure_device: domain:bus:dev = 0000:b0:00
    [ 5924.693976] libfcoe_device_notification: NETDEV_UNREGISTER eth6
    [ 5924.764979] libfcoe_device_notification: NETDEV_UNREGISTER eth14
    [ 5924.873539] libfcoe_device_notification: NETDEV_UNREGISTER eth15
    [ 5924.995209] libfcoe_device_notification: NETDEV_UNREGISTER eth16
    [ 5926.114407] sxge 0000:b2:00.0: PCI INT A disabled
    [ 5926.119342] BUG: unable to handle kernel NULL pointer dereference at (null)
    [ 5926.127189] IP: [<ffffffff81353a3b>] pci_stop_bus_device+0x33/0x83
    [ 5926.133377] PGD 0
    [ 5926.135402] Oops: 0000 [#1] SMP
    [ 5926.138659] CPU 2
    [ 5926.140499] Modules linked in:
    ...
    [ 5926.143754]
    [ 5926.275823] Call Trace:
    [ 5926.278267] [<ffffffff81353a38>] pci_stop_bus_device+0x30/0x83
    [ 5926.284180] [<ffffffff81353af4>] pci_remove_bus_device+0x1a/0xba
    [ 5926.290264] [<ffffffff81366311>] pciehp_unconfigure_device+0x110/0x17b
    [ 5926.296866] [<ffffffff81365dd9>] ? pciehp_disable_slot+0x188/0x188
    [ 5926.303123] [<ffffffff81365d6f>] pciehp_disable_slot+0x11e/0x188
    [ 5926.309206] [<ffffffff81365e68>] pciehp_power_thread+0x8f/0xe0
    ...

    +-[0000:80]-+-00.0-[81-8f]--
    | +-01.0-[90-9f]--
    | +-02.0-[a0-af]--
    | +-02.2-[b0-bf]----00.0-[b1-b3]--+-02.0-[b2]--+-00.0 Device
    | | | +-00.1 Device
    | | | +-00.2 Device
    | | | \-00.3 Device
    | | \-03.0-[b3]--+-00.0 Device
    | | +-00.1 Device
    | | +-00.2 Device
    | | \-00.3 Device

    root complex: 80:02.2
    pci express modules: have pcie switch and are listed as b0:00.0, b1:02.0 and b1:03.0.
    end devices are b2:00.0 and b3.00.0.
    VFs are: b2:00.1,... b2:00.3, and b3:00.1,...,b3:00.3

    Root cause: when doing pci_stop_bus_device() with phys fn, it will stop virt fn and
    remove the fn, so
    list_for_each_safe(l, n, &bus->devices)
    will have problem to refer freed n that is pointed to vf entry.

    Solution is just replacing list_for_each_safe() with list_for_each().
    pci_stop_bus_device(dev) will not remove dev from bus->devices list,
    so We only need use for_each here.

    During reviewing the patch, Bjorn said:
    | The PCI hot-remove path calls pci_stop_bus_devices() via
    | pci_remove_bus_device().
    |
    | pci_stop_bus_devices() traverses the bus->devices list (point A below),
    | stopping each device in turn, which calls the driver remove() method. When
    | the device is an SR-IOV PF, the driver calls pci_disable_sriov(), which
    | also uses pci_remove_bus_device() to remove the VF devices from the
    | bus->devices list (point B).
    |
    | pci_remove_bus_device
    | pci_stop_bus_device
    | pci_stop_bus_devices(subordinate)
    | list_for_each(bus->devices) <-- A
    | pci_stop_bus_device(PF)
    | ...
    | driver->remove
    | pci_disable_sriov
    | ...
    | pci_remove_bus_device(VF)
    | <remove from bus_list> <-- B
    |
    | At B, we're changing the same list we're iterating through at A, so when
    | the driver remove() method returns, the pci_stop_bus_devices() iterator has
    | a pointer to a list entry that has already been freed.

    Discussion thread can be found : https://lkml.org/lkml/2011/10/15/141

    -v2: updated changelog.
    -v3: According to Kenji, do not allocate another list for PF.
    Also We don't need to check dev->is_virtfn anymore, because PF should come
    first in the list, and even VF come first, it is still ok.
    -v4: According to Kenji, expand list_for_each(), and add is_virtfn checking

    Signed-off-by: Yinghai Lu <yinghai@kernel.org>

    ---
    drivers/pci/remove.c | 28 +++++++++++++++++++++++++++-
    1 file changed, 27 insertions(+), 1 deletion(-)

    Index: linux-2.6/drivers/pci/remove.c
    ===================================================================
    --- linux-2.6.orig/drivers/pci/remove.c
    +++ linux-2.6/drivers/pci/remove.c
    @@ -123,10 +123,36 @@ void pci_remove_behind_bridge(struct pci
    static void pci_stop_bus_devices(struct pci_bus *bus)
    {
    struct list_head *l, *n;
    + struct list_head *head = &bus->devices;

    + /*
    + * pci_stop_bus_device(dev) will not remove dev from bus->devices list,
    + * so We don't need use _safe version for_each here.
    + * Also _safe version has problem when pci_stop_bus_device() for PF try
    + * to remove VFs.
    + */
    + for (l = head->next; l != head;) {
    + struct pci_dev *dev = pci_dev_b(l);
    +
    + /*
    + * VFs are removed by pci_remove_bus_device() in the
    + * pci_stop_bus_devices() code path for PF.
    + * aka, bus->devices get updated in the process.
    + * barrier() will make sure we get right next from that list.
    + */
    + if (!dev->is_virtfn) {
    + pci_stop_bus_device(dev);
    + barrier();
    + }
    + l = l->next;
    + }
    +
    + /* For left over VFs in case */
    list_for_each_safe(l, n, &bus->devices) {
    struct pci_dev *dev = pci_dev_b(l);
    - pci_stop_bus_device(dev);
    +
    + if (dev->is_virtfn)
    + pci_stop_bus_device(dev);
    }
    }


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