Re: [PATCH] pci/pciehp: bail on bogus pcie reads from removed devices

Jarod Wilson
2015-08-04T17:25:19Z

On 8/4/2015 12:56 PM, Bjorn Helgaas wrote:
> On Tue, Aug 04, 2015 at 10:05:18AM -0400, Jarod Wilson wrote:
>> On Mon, Aug 3, 2015 at 12:14 AM, Bjorn Helgaas <bhelgaas@google.com> wrote:
>>
>>> On Tue, Jul 21, 2015 at 12:25:30PM -0400, Jarod Wilson wrote:
>>>> https://bugzilla.kernel.org/show_bug.cgi?id=99841
>>>>
>>>> Seems like a read of all 1's from a register of a device that has gone
>>>> away should be taken as a sign that the device has gone away.
>>>> Section 6.2.10 of the PCIE spec (v4.0, rev 0.3, Feb 19, 2014) suggests as
>>>> much with this snippet:
>>>>
>>>> |IMPLEMENTATION NOTE
>>>> |Data Value of All 1’s
>>>> |Many platforms, including those supporting RP Extensions for DPC, can
>>>> |return a data value of all 1’s to software when an error is associated
>>>> |with a PCI Express Configuration, I/O, or Memory Read Request. During
>>> DPC,
>>>> |the Downstream Port discards Requests destined for the Link and
>>> completes
>>>> |them with an error (i.e., either with an Unsupported Request (UR) or
>>>> |Completer Abort (CA) Completion Status). By ending a series of MMIO or
>>>> |configuration space operations with a read to an address with a known
>>>> |data value not equal to all 1’s, software may determine if a Completer
>>>> |has been removed or DPC has been triggered.
>>>>
>>>> I'm not sure the above is directly relevant to this case, but the same
>>>> principle (reading all 1's means the device is probably gone) seems to
>>>> hold.
>>>>
>>>> This is based on part of a debugging patch Bjorn posted in the referenced
>>>> bugzilla, and its required to make the HP ZBook G2 I've got here not barf
>>>> when disconnecting a thunderbolt ethernet adapter and corrupt memory.
>>>>
>>>> Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
>>>> CC: Bjorn Helgaas <bhelgaas@google.com>
>>>> CC: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>>> CC: linux-pci@vger.kernel.org
>>>> Signed-off-by: Jarod Wilson <jarod@redhat.com>
>>>
>>> Hi Jarod,
>>>
>>> I think there are two issues here:
>>>
>>> 1) pciehp doesn't handle all 1's correctly
>>> 2) use-after-free of hotplug_slot
>>>
>>> This patch is for the first issue. I think it's correct, but I still
>>> have a question or two. I attached an updated version of the patch
>>> and changelog.
>>>
>>> Here's the path I think we're taking: 03:03.0 receives pciehp
>>> interrupt for removal (link down and card not present), and we call
>>> pciehp_unconfigure_device() for 05:00.0 and everything downstream from
>>> it. Part of this is removing 06:00.0. I expected this would use this
>>> path:
>>>
>>> pcie_port_remove_service # .remove method for 06:00.0
>>> dev_printk("unloading service driver ...")
>>> pciehp_remove # hpdriver_portdrv.remove
>>> pciehp_release_ctrl
>>> pcie_shutdown_notification
>>> pcie_disable_notification
>>> pcie_write_cmd
>>> pcie_do_write_cmd(..., true) # wait
>>> pcie_wait_cmd
>>> pcie_poll_cmd
>>> read PCI_EXP_SLTSTA # would get 0xffff
>>> read PCI_EXPT_SLTCTL # would get 0xffff
>>>
>>> so I added checks for ~0 data in pcie_poll_cmd() and
>>> pcie_do_write_cmd().
>>>
>>> But the dmesg log shows that we were in pcie_isr(), and I don't
>>> understand yet how we got there. Can you help figure that out? Maybe
>>> put a dump_stack() in pcie_isr() or something?
>>
>> [ 1949.102247] pciehp 0000:03:03.0:pcie24: pcie_isr: intr_loc 108
>> [ 1949.102252] pciehp 0000:03:03.0:pcie24: Presence/Notify input change
>> [ 1949.102256] pciehp 0000:03:03.0:pcie24: Card not present on Slot(3)
>> [ 1949.102262] pciehp 0000:03:03.0:pcie24: Data Link Layer State change
>> [ 1949.102266] pciehp 0000:03:03.0:pcie24: slot(3): Link Down event
>> [ 1949.102281] pciehp 0000:03:03.0:pcie24: Surprise Removal
>> [ 1949.102286] pciehp 0000:03:03.0:pcie24: Link Down event ignored on
>> slot(3): already powering off
>> [ 1949.102288] pciehp 0000:03:03.0:pcie24: Disabling
>> domain:bus:device=0000:05:00
>> [ 1949.102290] pciehp 0000:03:03.0:pcie24: pciehp_unconfigure_device:
>> domain:bus:dev = 0000:05:00
>> [ 1950.321907] tg3 0000:07:00.0: tg3_abort_hw timed out, TX_MODE_ENABLE
>> will not clear MAC_TX_MODE=ffffffff
>> [ 1950.525986] [sched_delayed] sched: RT throttling activated
>> [ 1950.544164] pciehp 0000:06:00.0:pcie24: unloading service driver pciehp
>> [ 1950.544170] pciehp 0000:06:00.0:pcie24: release_slot: physical_slot = 9
>> [ 1950.545016] pciehp 0000:06:00.0:pcie24: Timeout on hotplug command
>> 0x1038 (issued 19092 msec ago)
>> [ 1950.545020] pciehp 0000:06:00.0:pcie24: pcie_do_write_cmd: no response
>> from device
>> [ 1950.545021] pciehp 0000:06:00.0:pcie24: pcie_disable_notification:
>> SLOTCTRL d8 write cmd 0
>> [ 1950.545025] pciehp 0000:06:00.0:pcie24: Device has gone away
>> [ 1950.545027] CPU: 0 PID: 12361 Comm: kworker/0:2 Not tainted
>> 3.10.0-302.el7.hp.x86_64 #1
>> [ 1950.545028] Hardware name: Hewlett-Packard HP ZBook 15 G2/2253, BIOS M70
>> Ver. 01.07 02/26/2015
>> [ 1950.545033] Workqueue: pciehp-3 pciehp_power_thread
>> [ 1950.545034] 0000000000000000 00000000f721dd13 ffff8804822ffa78
>> ffffffff81632729
>> [ 1950.545036] ffff8804822ffac0 ffffffff8133bf64 ffff00000000002e
>> 00000000f721dd13
>> [ 1950.545038] ffff8804818fab00 ffff880468f70cc0 000000000000002e
>> 0000000000000282
>> [ 1950.545039] Call Trace:
>> [ 1950.545044] [<ffffffff81632729>] dump_stack+0x19/0x1b
>> [ 1950.545046] [<ffffffff8133bf64>] pcie_isr+0x264/0x280
>> [ 1950.545048] [<ffffffff8111b6b9>] __free_irq+0x189/0x220
>> [ 1950.545049] [<ffffffff8111b7e9>] free_irq+0x49/0xb0
>> [ 1950.545051] [<ffffffff8133d3b9>] pciehp_release_ctrl+0xb9/0xe0
>> [ 1950.545053] [<ffffffff81339db3>] pciehp_remove+0x23/0x30
>> [ 1950.545055] [<ffffffff8133442e>] pcie_port_remove_service+0x4e/0x60
>
> Do you have CONFIG_DEBUG_SHIRQ set? When CONFIG_DEBUG_SHIRQ is set,
> __free_irq() calls the ISR one last time. It does make sense that the
> driver must be prepared for the ISR to be called at any time before
> free_irq() returns. I just didn't see a path for the already-removed
> device to generate an actual interrupt.

Yup, I've got CONFIG_DEBUG_SHIRQ=y in my config. So I take it we're
hitting the action->handler(irq, dev_id) bit in __free_irq(), after
we've already done a bunch of teardown/removal?

> Can you try the version I posted, with the additional tests in
> pcie_poll_cmd() and pcie_do_write_cmd()? We should try to read from
> the device there, even before we free the IRQ, so we might see several
> messages. Maybe there's a way we can be smarter about bailing out
> there.

The above was with your additions munged in with the older patch, I
actually do see "pcie_do_write_cmd: no response from device" just two
lines ahead of each "Device has gone away" message from pcie_isr().

pciehp 0000:06:00.0:pcie24: pcie_do_write_cmd: no response from device
pciehp 0000:06:00.0:pcie24: pcie_disable_notification: SLOTCTRL d8 write
cmd 0
pciehp 0000:06:00.0:pcie24: Device has gone away <- from pcie_isr()

--
Jarod Wilson
jarod@redhat.com