Message-ID: <20150804175141.GC17327@google.com>
Date:	Tue, 4 Aug 2015 12:51:41 -0500
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Jarod Wilson <jarod@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci/pciehp: bail on bogus pcie reads from removed devices

On Tue, Aug 04, 2015 at 01:21:23PM -0400, Jarod Wilson wrote:
> 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@...gle.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@...gle.com>
> >>>>CC: Bjorn Helgaas <bhelgaas@...gle.com>
> >>>>CC: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >>>>CC: linux-pci@...r.kernel.org
> >>>>Signed-off-by: Jarod Wilson <jarod@...hat.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?

OK, good, that explains why we called pcie_isr().

> >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()

Oh, sorry!  I should have noticed that.  I just wanted to make sure I
didn't cause a flood of extra messages.

I think I'll merge this version (with all three checks).  We still have a
slot lifetime issue, but that's a separate problem.

Bjorn
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