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    SubjectRe: [RESEND PATCH] PCI: Make sriov work with hotplug remove
    (2011/11/17 6:23), Yinghai Lu wrote:
    > On 11/15/2011 09:54 PM, Kenji Kaneshige wrote:
    >
    >> Sorry for the delayed comment.
    >>
    >> I don't think allocating new memory for device removal is good idea. And
    >> your code doesn't seem to work if memory allocation failed. What about
    >> something like below? Note that it is not tested at all, sorry.
    >>
    >
    > Yes, it should work.
    >
    > I updated the patch, use list_entry_for_each directly. also remove VF checking.
    >
    > Please check it.
    >
    > Thanks
    >
    > Yinghai
    >
    > Subject: [PATCH -v3] 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.

    I think we should not have an assumption that PF comes first in
    the list. So I think dev->is_virtfn check is needed.

    On the other hand, if we add the dev->is_virtfn check,
    pci_stop_bus_devices() doesn't work for buses whose &bus->devices
    list have only VFs(, though I think pci_stop_bus_devices() is not
    used for this kind of bus currently). How about adding the
    pci_stop_bus_device() loop for VFs after the loop for PFs, as you
    did in your first try?

    >
    > Signed-off-by: Yinghai Lu<yinghai@kernel.org>
    >
    > ---
    > drivers/pci/remove.c | 17 +++++++++++++++--
    > 1 file changed, 15 insertions(+), 2 deletions(-)
    >
    > Index: linux-2.6/drivers/pci/remove.c
    > ===================================================================
    > --- linux-2.6.orig/drivers/pci/remove.c
    > +++ linux-2.6/drivers/pci/remove.c
    > @@ -122,11 +122,24 @@ 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 *l;
    >
    > - list_for_each_safe(l, n,&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.
    > + */
    > + list_for_each(l,&bus->devices) {
    > struct pci_dev *dev = pci_dev_b(l);
    > pci_stop_bus_device(dev);
    > + /*
    > + * 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.
    > + */
    > + barrier();

    I think we should not use list_for_each() because

    - difficult to understand the intention of the barrier().
    - might not work if list_for_each() implementation were changed.

    Regards,
    Kenji Kaneshige


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