Message-ID: <8f5e28dd-9e21-0381-5b32-0850f9f039ca@linux.intel.com>
Date: Thu, 26 Jun 2025 12:22:43 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: D Scott Phillips <scott@...amperecomputing.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

On Wed, 25 Jun 2025, D Scott Phillips wrote:

> 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)`.

Yes, it should have been without that ~. Can you test the change with 
that changed? I'm sorry about the extra trouble.

> 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
> 

-- 
 i.

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