Re: [PATCH 1/7] PCI: Make sriov work with hotplug remove

From: Yinghai Lu
Date: Mon Jan 23 2012 - 17:30:42 EST

On Mon, Jan 23, 2012 at 1:34 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> On Mon, Jan 23, 2012 at 11:44 AM, Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>> On Mon, Jan 23, 2012 at 11:36 AM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
>>>
>>> Maybe we can put VF and PF in bus->devices like:
>>> VF come first than PF?
>>
>> Ugh. Ok, so that's a disgusting hack, but it's better than messing up
>> the generic PCI subsystem. At least it's a disgusting hack in the IOV
>> code.
>
> just tested, the patch with this hack works.
>
>>
>> I still would prefer to just do the virtual devices right instead. Or
>> even just make the removal loop inherently robust, rather than have
>> that insane knowledge of virtual function devices that were done so
>> horribly wrong.

for_each_prev_safe is working...

please check attached patch...

Thanks

Yinghai
Subject: [PATCH -v5] 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

-v5: According to Linus to make remove more robust, Change to list_for_each_prev_safe
instead. That is more reasonable, because those devices are added to tail of
the list before.

Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>

---
drivers/pci/remove.c | 10 +++++++++-
1 file changed, 9 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
@@ -128,7 +128,15 @@ static void pci_stop_bus_devices(struct
{
struct list_head *l, *n;

- list_for_each_safe(l, n, &bus->devices) {
+ /*
+ * VFs could be removed by pci_remove_bus_device() in the
+ * pci_stop_bus_devices() code path for PF.
+ * aka, bus->devices get updated in the process.
+ * but VFs are inserted after PFs when SRIOV is enabled for PF,
+ * We can iterate the list backwards to get prev valid PF instead
+ * of removed VF.
+ */
+ list_for_each_prev_safe(l, n, &bus->devices) {
struct pci_dev *dev = pci_dev_b(l);
pci_stop_bus_device(dev);
}