Message-ID: <86ms9vlfxr.fsf@scott-ph-mail.amperecomputing.com>
Date: Wed, 25 Jun 2025 13:33:20 -0700
From: D Scott Phillips <scott@...amperecomputing.com>
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>
Subject: Re: [PATCH 24/25] PCI: Perform reset_resource() and build fail list
 in sync

Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> writes:

> On Wed, 18 Jun 2025, D Scott Phillips wrote:
>
>> Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com> writes:
>> 
>> > 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>
>> 
>> Hi Ilpo, I'm seeing a crash on arm64 at boot that I bisected to this
>> change. I don't think it's the same as the other issues reported. I've
>> confirmed the crash is still there after your follow up patches.  The
>> crash itself is below[1].
>> 
>> It looks like the problem begins when:
>> 
>> amdgpu_device_resize_fb_bar()
>>  pci_resize_resource()
>>   pci_reassign_bridge_resources()
>>    __pci_bus_size_bridges()
>> 
>> adds pci_hotplug_io_size to `realloc_head`. The io resource allocation
>> has failed earlier because the root port doesn't have an io window[2].
>> 
>> Then with this patch, pci_reassign_bridge_resources()'s call to
>> __pci_bridge_assign_resources() now returns the io added space for
>> hotplug in the `failed` list where the old code dropped it and did not.
>> 
>> That sends pci_reassign_bridge_resources() into the `cleanup:` path,
>> where I think the cleanup code doesn't properly release the resources
>> that were assigned by __pci_bridge_assign_resources() and there's a
>> conflict reported in pci_claim_resource() where a restored resource is
>> found as conflicting with itself:
>> 
>> > pcieport 000d:00:01.0: bridge window [mem 0x340000000000-0x340017ffffff 64bit pref]: can't claim; address conflict with PCI Bus 000d:01 [mem 0x340000000000-0x340017ffffff 64bit pref]
>> 
>> Setting `pci=hpiosize=0` avoids this crash, as does this change:
>> 
>> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
>> index 16d5d390599a..59ece11702da 100644
>> --- a/drivers/pci/setup-bus.c
>> +++ b/drivers/pci/setup-bus.c
>> @@ -2442,7 +2442,7 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
>>  	LIST_HEAD(saved);
>>  	LIST_HEAD(added);
>>  	LIST_HEAD(failed);
>> -	unsigned int i;
>> +	unsigned int i, relevant_fails;
>>  	int ret;
>>  
>>  	down_read(&pci_bus_sem);
>> @@ -2490,7 +2490,16 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
>>  	__pci_bridge_assign_resources(bridge, &added, &failed);
>>  	BUG_ON(!list_empty(&added));
>>  
>> -	if (!list_empty(&failed)) {
>> +	relevant_fails = 0;
>> +	list_for_each_entry(dev_res, &failed, list) {
>> +		restore_dev_resource(dev_res);
>> +		if (((dev_res->res->flags ^ type) & PCI_RES_TYPE_MASK) == 0)
>> +			relevant_fails++;
>> +	}
>> +	free_list(&failed);
>> +
>> +	/* Cleanup if we had failures in resources of interest */
>> +	if (relevant_fails != 0) {
>>  		ret = -ENOSPC;
>>  		goto cleanup;
>>  	}
>> @@ -2509,11 +2518,6 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
>>  	return 0;
>>  
>>  cleanup:
>> -	/* Restore size and flags */
>> -	list_for_each_entry(dev_res, &failed, list)
>> -		restore_dev_resource(dev_res);
>> -	free_list(&failed);
>> -
>>  	/* Revert to the old configuration */
>>  	list_for_each_entry(dev_res, &saved, list) {
>>  		struct resource *res = dev_res->res;
>> 
>> I don't know this code well enough to know if that changes is completely
>> bonkers or what.
>
> Hi again,
>
> Thanks for all the details what you think went wrong, it was really 
> useful. I think you have it towards the right direction but a more 
> targetted seems enough to address this (this needs to be confirmed, please
> test the patch below).
>
> The most correct solution would be to make all the resource fitting code 
> to focus on the resources that match the type filter. However, that looks 
> way too scary change at the moment to implement, and especially, let it 
> end up into stable (to fix this issue). So it looks this somewhat band-aid 
> solution similar to your attempt might be better as a fix for now.
>
> In medium term, I'd want to avoid using type as a filter and base all 
> such decisions on matching the bridge window resource the dev resource 
> belongs to. I've some work towards that direction already which removes 
> lots of complexity in which bridge window is going to be selected as 
> there will be a single place to make always the same decision. That change 
> is also going to simplify the internal interfaces between functions very 
> noticably (but the change require more testing before I've enough 
> confidence to submit it). That work doesn't cover this resize side yet but 
> it should be extended there as well.
>
> So please test this somewhat band-aid patch:
>
> From 971686ed85e341e7234f8fe8b666140187f63ad1 Mon Sep 17 00:00:00 2001
> From: =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= <ilpo.jarvinen@...ux.intel.com>
> Date: Wed, 25 Jun 2025 20:30:43 +0300
> Subject: [PATCH 1/1] PCI: Fix failure detectiong during resource resize

detection

> MIME-Version: 1.0
> Content-Type: text/plain; charset=UTF-8
> Content-Transfer-Encoding: 8bit
>
> Since the commit 96336ec70264 ("PCI: Perform reset_resource() and build
> fail list in sync") the failed list is always built and returned to let
> the caller decide if what to do with the failures. The caller may want
> to retry resource fitting and assignment and before that can happen,
> the resources should be restored to their original state (a reset
> effectively clears the struct resource), which requires returning them
> on the failed list so that the original state remains stored in the
> associated struct pci_dev_resource.
>
> Resource resizing is different from the ordinary resource fitting and
> assignment in that it only considers part of the resources. This means
> failures for other resource types are not relevant at all and should be
> ignored. As resize doesn't unassign such unrelated resources, those
> resource ending up into the failed list implies assignment of that
> resource must have failed before resize too. The check in
> pci_reassign_bridge_resources() to decide if the whole assignment is
> successful, however, is based on list emptiness which may cause false
> negatives when the failed list resources with unrelated type.
>
> If the failed list is not empty, call pci_required_resource_failed()
> and extend it to be able to filter on specific resource types too (if
> provided).
>
> Calling pci_required_resource_failed() at this point is slightly
> problematic because the resource itself is reset when the failed list
> is constructed in __assign_resources_sorted(). As a result,
> pci_resource_is_optional() does not have access to the original
> resource flags. This could be worked around by restoring and
> re-reseting the resource around the call to pci_resource_is_optional(),
> however, it shouldn't cause issue as resource resizing is meant for
> 64-bit prefetchable resources according to Christian König (see the
> Link which unfortunately doesn't point directly to Christian's reply
> because lore didn't store that email at all).
>
> Link: https://lore.kernel.org/all/c5d1b5d8-8669-5572-75a7-0b480f581ac1@linux.intel.com/
> Reported-by: D Scott Phillips <scott@...amperecomputing.com>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> Cc: Christian König <christian.koenig@....com>
> ---
>  drivers/pci/setup-bus.c | 26 ++++++++++++++++++--------
>  1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 07c3d021a47e..8284bbdc44b4 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -28,6 +28,10 @@
>  #include <linux/acpi.h>
>  #include "pci.h"
>  
> +#define PCI_RES_TYPE_MASK \
> +	(IORESOURCE_IO | IORESOURCE_MEM | IORESOURCE_PREFETCH |\
> +	 IORESOURCE_MEM_64)
> +
>  unsigned int pci_flags;
>  EXPORT_SYMBOL_GPL(pci_flags);
>  
> @@ -384,13 +388,19 @@ static bool pci_need_to_release(unsigned long mask, struct resource *res)
>  }
>  
>  /* Return: @true if assignment of a required resource failed. */
> -static bool pci_required_resource_failed(struct list_head *fail_head)
> +static bool pci_required_resource_failed(struct list_head *fail_head,
> +					 unsigned long type)
>  {
>  	struct pci_dev_resource *fail_res;
>  
> +	type &= ~PCI_RES_TYPE_MASK;

Is this meant to be `type &= PCI_RES_TYPE_MASK`? If not, then I think
the new `if` check below is effectively just `if (type)`.

FWIW, the patch in the current state is fixing the problem that I've
been hitting.

> +
>  	list_for_each_entry(fail_res, fail_head, list) {
>  		int idx = pci_resource_num(fail_res->dev, fail_res->res);
>  
> +		if (type && (fail_res->flags & PCI_RES_TYPE_MASK) != type)
> +			continue;
> +
>  		if (!pci_resource_is_optional(fail_res->dev, idx))
>  			return true;
>  	}
> @@ -504,7 +514,7 @@ static void __assign_resources_sorted(struct list_head *head,
>  	}
>  
>  	/* Without realloc_head and only optional fails, nothing more to do. */
> -	if (!pci_required_resource_failed(&local_fail_head) &&
> +	if (!pci_required_resource_failed(&local_fail_head, 0) &&
>  	    list_empty(realloc_head)) {
>  		list_for_each_entry(save_res, &save_head, list) {
>  			struct resource *res = save_res->res;
> @@ -1704,10 +1714,6 @@ static void __pci_bridge_assign_resources(const struct pci_dev *bridge,
>  	}
>  }
>  
> -#define PCI_RES_TYPE_MASK \
> -	(IORESOURCE_IO | IORESOURCE_MEM | IORESOURCE_PREFETCH |\
> -	 IORESOURCE_MEM_64)
> -
>  static void pci_bridge_release_resources(struct pci_bus *bus,
>  					 unsigned long type)
>  {
> @@ -2445,8 +2451,12 @@ int pci_reassign_bridge_resources(struct pci_dev *bridge, unsigned long type)
>  		free_list(&added);
>  
>  	if (!list_empty(&failed)) {
> -		ret = -ENOSPC;
> -		goto cleanup;
> +		if (pci_required_resource_failed(&failed, type)) {
> +			ret = -ENOSPC;
> +			goto cleanup;
> +		}
> +		/* Only resources with unrelated types failed (again) */
> +		free_list(&failed);
>  	}
>  
>  	list_for_each_entry(dev_res, &saved, list) {
>
> base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
> -- 
> 2.39.5

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