Message-ID: <6e4b340b-a239-4550-b091-139c3724a54c@linaro.org>
Date: Wed, 28 May 2025 12:39:53 +0100
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
 Michał Winiarski <michal.winiarski@...el.com>,
 Igor Mammedov <imammedo@...hat.com>, LKML <linux-kernel@...r.kernel.org>,
 Mika Westerberg <mika.westerberg@...ux.intel.com>,
 William McVicker <willmcvicker@...gle.com>
Subject: Re: [PATCH 24/25] PCI: Perform reset_resource() and build fail list
 in sync



On 5/28/25 12:22 PM, Tudor Ambarus wrote:
> 
> On 5/6/25 4:53 PM, Ilpo Järvinen wrote:
>> On Tue, 6 May 2025, Tudor Ambarus wrote:
>>
>>> Hi!
>>>
>>> On 12/16/24 5:56 PM, Ilpo Järvinen wrote:
>>>> Resetting resource is problematic as it prevent attempting to allocate
>>>> the resource later, unless something in between restores the resource.
>>>> Similarly, if fail_head does not contain all resources that were reset,
>>>> those resource cannot be restored later.
>>>>
>>>> The entire reset/restore cycle adds complexity and leaving resources
>>>> into reseted state causes issues to other code such as for checks done
>>>> in pci_enable_resources(). Take a small step towards not resetting
>>>> resources by delaying reset until the end of resource assignment and
>>>> build failure list (fail_head) in sync with the reset to avoid leaving
>>>> behind resources that cannot be restored (for the case where the caller
>>>> provides fail_head in the first place to allow restore somewhere in the
>>>> callchain, as is not all callers pass non-NULL fail_head).
>>>>
>>>> The Expansion ROM check is temporarily left in place while building the
>>>> failure list until the upcoming change which reworks optional resource
>>>> handling.
>>>>
>>>> Ideally, whole resource reset could be removed but doing that in a big
>>>> step would make the impact non-tractable due to complexity of all
>>>> related code.
>>>>
>>>> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
>>> I'm hitting the BUG_ON(!list_empty(&add_list)); in
>>> pci_assign_unassigned_bus_resources() [1] with 6.15-rc5 and the the
>>> pixel6 downstream pcie driver.
>>>
>>> I saw the thread where "a34d74877c66 PCI: Restore assigned resources
>>> fully after release" fixes things for some other cases, but it's not the
>>> case here.
>>>
>>> Reverting the following patches fixes the problem:
>>> a34d74877c66 PCI: Restore assigned resources fully after release
>>> 2499f5348431 PCI: Rework optional resource handling
>>> 96336ec70264 PCI: Perform reset_resource() and build fail list in sync
>> So it's confirmed that you needed to revert also this last commit 
>> 96336ec70264, not just the rework change?
> I needed to revert 96336ec70264 as well otherwise the build fails.
>>> In the working case the add_list list is empty throughout the entire
>>> body of pci_assign_unassigned_bus_resources().
>>>
>>> In the failing case __pci_bus_size_bridges() leaves the add_list not
>>> empty and __pci_bus_assign_resources() does not consume the list, thus
>>> the BUG_ON. The failing case contains an extra print that's not shown
>>> when reverting the blamed commits:
>>> [   13.951185][ T1101] pcieport 0000:00:00.0: bridge window [mem
>>> 0x00100000-0x001fffff] to [bus 01-ff] add_size 100000 add_align 100000
>>>
>>> I've added some prints trying to describe the code path, see
>>> https://paste.ofcode.org/Aeu2YBpLztc49ZDw3uUJmd#
>>>
>>> Failing case:
>>> [   13.944231][ T1101] pci 0000:01:00.0: [144d:a5a5] type 00 class
>>> 0x000000 PCIe Endpoint
>>> [   13.944412][ T1101] pci 0000:01:00.0: BAR 0 [mem
>>> 0x00000000-0x000fffff 64bit]
>>> [   13.944532][ T1101] pci 0000:01:00.0: ROM [mem 0x00000000-0x0000ffff
>>> pref]
>>> [   13.944649][ T1101] pci 0000:01:00.0: enabling Extended Tags
>>> [   13.944844][ T1101] pci 0000:01:00.0: PME# supported from D0 D3hot D3cold
>>> [   13.945015][ T1101] pci 0000:01:00.0: 15.752 Gb/s available PCIe
>>> bandwidth, limited by 8.0 GT/s PCIe x2 link at 0000:00:00.0 (capable of
>>> 31.506 Gb/s with 16.0 GT/s PCIe x2 link)
>>> [   13.950616][ T1101] __pci_bus_size_bridges: before pbus_size_mem.
>>> list empty? 1
>>> [   13.950784][ T1101] pbus_size_mem: 2. list empty? 1
>>> [   13.950886][ T1101] pbus_size_mem: 1 list empty? 0
>>> [   13.950982][ T1101] pbus_size_mem: 3. list empty? 0
>>> [   13.951082][ T1101] pbus_size_mem: 4. list empty? 0
>>> [   13.951185][ T1101] pcieport 0000:00:00.0: bridge window [mem
>>> 0x00100000-0x001fffff] to [bus 01-ff] add_size 100000 add_align 100000
>>> [   13.951448][ T1101] __pci_bus_size_bridges: after pbus_size_mem. list
>>> empty? 0
>>> [   13.951643][ T1101] pci_assign_unassigned_bus_resources: before
>>> __pci_bus_assign_resources -> list empty? 0
>>> [   13.951924][ T1101] pcieport 0000:00:00.0: bridge window [mem
>>> 0x40000000-0x401fffff]: assigned
>>> [   13.952248][ T1101] pci_assign_unassigned_bus_resources: after
>>> __pci_bus_assign_resources -> list empty? 0
>>> [   13.952634][ T1101] ------------[ cut here ]------------
>>> [   13.952818][ T1101] kernel BUG at drivers/pci/setup-bus.c:2514!
>>> [   13.953045][ T1101] Internal error: Oops - BUG: 00000000f2000800 [#1]
>>>  SMP
>>> ...
>>> [   13.976086][ T1101] Call trace:
>>> [   13.976206][ T1101]  pci_assign_unassigned_bus_resources+0x110/0x114 (P)
>>> [   13.976462][ T1101]  pci_rescan_bus+0x28/0x48
>>> [   13.976628][ T1101]  exynos_pcie_rc_poweron
>>>
>>> Working case:
>>> [   13.786961][ T1120] pci 0000:01:00.0: [144d:a5a5] type 00 class
>>> 0x000000 PCIe Endpoint
>>> [   13.787136][ T1120] pci 0000:01:00.0: BAR 0 [mem
>>> 0x00000000-0x000fffff 64bit]
>>> [   13.787280][ T1120] pci 0000:01:00.0: ROM [mem 0x00000000-0x0000ffff
>>> pref]
>>> [   13.787541][ T1120] pci 0000:01:00.0: enabling Extended Tags
>>> [   13.787808][ T1120] pci 0000:01:00.0: PME# supported from D0 D3hot D3cold
>>> [   13.787988][ T1120] pci 0000:01:00.0: 15.752 Gb/s available PCIe
>>> bandwidth, limited by 8.0 GT/s PCIe x2 link at 0000:00:00.0 (capable of
>>> 31.506 Gb/s with 16.0 GT/s PCIe x2 link)
>>> [   13.795279][ T1120] __pci_bus_size_bridges: before pbus_size_mem.
>>> list empty? 1
>>> [   13.795408][ T1120] pbus_size_mem: 2. list empty? 1
>>> [   13.795495][ T1120] pbus_size_mem: 2. list empty? 1
>>> [   13.795577][ T1120] __pci_bus_size_bridges: after pbus_size_mem. list
>>> empty? 1
>>> [   13.795692][ T1120] pci_assign_unassigned_bus_resources: before
>>> __pci_bus_assign_resources -> list empty? 1
>>> [   13.795849][ T1120] pcieport 0000:00:00.0: bridge window [mem
>>> 0x40000000-0x401fffff]: assigned
>>> [   13.796072][ T1120] pci_assign_unassigned_bus_resources: after
>>> __pci_bus_assign_resources -> list empty? 1
>>> [   13.796662][ T1120] cpif: s5100_poweron_pcie: DBG: MSI sfr not set
>>> up, yet(s5100_pdev is NULL)
>>> [   13.796666][ T1120] cpif: register_pcie: s51xx_pcie_init start
>>>
>>>
>>> Any hints are welcomed. Thanks,
>>> ta
>> Hi and thanks for the report.
> Hi! Thanks for the help. I've been out of office for the last 2 weeks,
> sorry for the delayed reply.
> 
>> The interesting part occurs inside reassign_resources_sorted() where most 
>> items are eliminated from realloc_head by the list_del().
>>
>> My guess is that somehow, the change in 96336ec70264 from !res->flags
>> to the more complicated check somehow causes this. If the new check 
>> doesn't match and subsequently, no match is found from the head list, the 
>> loop will do continue and not remove the entry from realloc_head.
> I added a print right there and it seems it's something else. See below.
>> But it's hard to confirm without knowing what that resources realloc_head 
>> contains. Perhaps if you print the resources that are processed around 
>> that part of the code in reassign_resources_sorted(), comparing the log 
>> from the reverted code with the non-working case might help to understand 
>> what is different there and why. To understand better what is in the head 
>> list, it would be also useful to know from which device the resources were 
>> added into the head list in pdev_sort_resources().
>>
> I added the suggested prints
> (https://paste.ofcode.org/DgmZGGgS6D36nWEzmfCqMm) on top of v6.15 with
> the downstream PCIe pixel driver and I obtain the following. Note that
> all added prints contain "tudor" for differentiation.
> 
> [   15.211179][ T1107] pci 0001:01:00.0: [144d:a5a5] type 00 class
> 0x000000 PCIe Endpoint
> [   15.212248][ T1107] pci 0001:01:00.0: BAR 0 [mem
> 0x00000000-0x000fffff 64bit]
> [   15.212775][ T1107] pci 0001:01:00.0: ROM [mem 0x00000000-0x0000ffff
> pref]
> [   15.213195][ T1107] pci 0001:01:00.0: enabling Extended Tags
> [   15.213720][ T1107] pci 0001:01:00.0: PME# supported from D0 D3hot
> D3cold
> [   15.214035][ T1107] pci 0001:01:00.0: 15.752 Gb/s available PCIe
> bandwidth, limited by 8.0 GT/s PCIe x2 link at 0001:00:00.0 (capable of
> 31.506 Gb/s with 16.0 GT/s PCIe x2 link)
> [   15.222286][ T1107] pci 0001:01:00.0: tudor: 1: pbus_size_mem: BAR 0
> [mem 0x00000000-0x000fffff 64bit] list empty? 1
> [   15.222813][ T1107] pci 0001:01:00.0: tudor: 1: pbus_size_mem: ROM
> [mem 0x00000000-0x0000ffff pref] list empty? 1
> [   15.224429][ T1107] pci 0001:01:00.0: tudor: 2: pbus_size_mem: ROM
> [mem 0x00000000-0x0000ffff pref] list empty? 0
> [   15.224750][ T1107] pcieport 0001:00:00.0: bridge window [mem
> 0x00100000-0x001fffff] to [bus 01-ff] add_size 100000 add_align 100000
> 
> [   15.225393][ T1107] tudor : pci_assign_unassigned_bus_resources:
> before __pci_bus_assign_resources -> list empty? 0
> [   15.225594][ T1107] pcieport 0001:00:00.0: tudor:
> pdev_sort_resources: bridge window [mem 0x00100000-0x001fffff] resource
> added in head list
> [   15.226078][ T1107] pcieport 0001:00:00.0: bridge window [mem
> 0x40000000-0x401fffff]: assigned
> [   15.226419][ T1107] tudor : pci_assign_unassigned_bus_resources:
> after __pci_bus_assign_resources -> list empty? 0
> [   15.226442][ T1107] ------------[ cut here ]------------
> [   15.227587][ T1107] kernel BUG at drivers/pci/setup-bus.c:2522!
> [   15.227813][ T1107] Internal error: Oops - BUG: 00000000f2000800 [#1]
>  SMP
> ...
> [   15.251570][ T1107] Call trace:
> [   15.251690][ T1107]  pci_assign_unassigned_bus_resources+0x110/0x114 (P)
> [   15.251945][ T1107]  pci_rescan_bus+0x28/0x48
> 
> I obtain the following output when using the same prints adapted
> (https://paste.ofcode.org/37w7RnKkPaCxyNhi5yhZPbZ) and with the blamed
> commits reverted:
> a34d74877c66 PCI: Restore assigned resources fully after release
> 2499f5348431 PCI: Rework optional resource handling
> 96336ec70264 PCI: Perform reset_resource() and build fail list in sync
> 
> [   15.200456][ T1102] pci 0000:01:00.0: [144d:a5a5] type 00 class
> 0x000000 PCIe Endpoint
> [   15.200632][ T1102] pci 0000:01:00.0: BAR 0 [mem
> 0x00000000-0x000fffff 64bit]
> [   15.200755][ T1102] pci 0000:01:00.0: ROM [mem 0x00000000-0x0000ffff
> pref]
> [   15.200876][ T1102] pci 0000:01:00.0: enabling Extended Tags
> [   15.201075][ T1102] pci 0000:01:00.0: PME# supported from D0 D3hot D3cold
> [   15.201254][ T1102] pci 0000:01:00.0: 15.752 Gb/s available PCIe
> bandwidth, limited by 8.0 GT/s PCIe x2 link at 0000:00:00.0 (capable of
> 31.506 Gb/s with 16.0 GT/s PCIe x2 link)
> [   15.206555][ T1102] pci 0000:01:00.0: tudor: 1: pbus_size_mem: BAR 0
> [mem 0x00000000-0x000fffff 64bit] list empty? 1
> [   15.206737][ T1102] pci 0000:01:00.0: tudor: 1: pbus_size_mem: ROM
> [mem 0x00000000-0x0000ffff pref] list empty? 1
> [   15.206901][ T1102] tudor : pci_assign_unassigned_bus_resources:
> before __pci_bus_assign_resources -> list empty? 1
> [   15.207072][ T1102] pcieport 0000:00:00.0: tudor:
> pdev_sort_resources: bridge window [mem 0x00100000-0x002fffff] resource
> added in head list
> [   15.207396][ T1102] pcieport 0000:00:00.0: bridge window [mem
> 0x40000000-0x401fffff]: assigned
> [   15.208165][ T1102] tudor : pci_assign_unassigned_bus_resources:
> after __pci_bus_assign_resources -> list empty? 1
> [   15.208783][ T1102] cpif: s5100_poweron_pcie: DBG: MSI sfr not set
> up, yet(s5100_pdev is NULL)
> [   15.208786][ T1102] cpif: register_pcie: s51xx_pcie_init start

I see my email client split the lines for the prints making the output
very hard to read. Added the output here too:
https://paste.ofcode.org/AEfjASQW8Z2jbMak5VkmpJ

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