Re: [PATCH 1/1] PCI: Fix premature removal from realloc_head list

[Bjorn Helgaas]

On Fri, Mar 13, 2026 at 10:45:50AM +0200, Ilpo Järvinen wrote:
> reassign_resources_sorted() checks for two things:
> 
> a) Resource assignment failures for mandatory resources by checking if
>    the resource remains unassigned, which are known to always repeat,
>    and does not attempt to assign them again.
> 
> b) That resource is not among the ones being processed/assigned at this
>    stage, leading to skip processing such resources in
>    reassign_resources_sorted() as well (resource assignment progresses
>    one PCI hierarchy level at a time).
> 
> The problem here is that a) is checked before b) but b) also implies
> the resources is not being assigned yet, making also a) true. As a)
> only skips resource assignment but still removes the resource from
> realloc_head, the later stages that would need to process the
> information in realloc_head cannot obtain the optional size information
> anymore. This leads to considering only non-optional part for bridge
> windows deeper in the PCI hierarchy.
> 
> This problem has been observed during rescan (add_size is not
> considered while attempting assignment for 0000:e2:00.0 indicating the
> corresponding entry was removed from realloc_head while processing
> resource assignments for 0000:e1):
> 
> pci_bus 0000:e1: scanning bus
> ...
> pci 0000:e3:01.0: bridge window [mem 0x800000000-0x1000ffffff 64bit pref] to [bus e4] add_size 60c000000 add_align 800000000
> pci 0000:e3:01.0: bridge window [mem 0x00100000-0x000fffff] to [bus e4] add_size 200000 add_align 200000
> pci 0000:e3:02.0: disabling bridge window [mem 0x00000000-0x000fffff 64bit pref] to [bus e5] (unused)
> pci 0000:e2:00.0: bridge window [mem 0x800000000-0x1000ffffff 64bit pref] to [bus e3-e5] add_size 60c000000 add_align 800000000
> pci 0000:e2:00.0: bridge window [mem 0x00100000-0x001fffff] to [bus e3-e5] add_size 200000 add_align 200000
> pcieport 0000:e1:02.0: bridge window [io  size 0x2000]: can't assign; no space
> pcieport 0000:e1:02.0: bridge window [io  size 0x2000]: failed to assign
> pcieport 0000:e1:02.0: bridge window [io  0x1000-0x2fff]: resource restored
> pcieport 0000:e1:02.0: bridge window [io  0x1000-0x2fff]: resource restored
> pcieport 0000:e1:02.0: bridge window [io  size 0x2000]: can't assign; no space
> pcieport 0000:e1:02.0: bridge window [io  size 0x2000]: failed to assign
> pci 0000:e2:00.0: bridge window [mem 0x28f000000000-0x28f800ffffff 64bit pref]: assigned
> 
> Fixes: 96336ec70264 ("PCI: Perform reset_resource() and build fail list in sync")
> Reported-by: Peter Nisbet <peter.nisbet@xxxxxxxxx>
> Tested-by: Peter Nisbet <peter.nisbet@xxxxxxxxx>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>

Applied to pci/resource for v7.1, thanks, Ilpo!

> ---
> 
> There's no publically available report on this, thus no Link/Closes tags.
> 
>  drivers/pci/setup-bus.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
> index 61f769aaa2f6..b0b00f10e31c 100644
> --- a/drivers/pci/setup-bus.c
> +++ b/drivers/pci/setup-bus.c
> @@ -434,6 +434,10 @@ static void reassign_resources_sorted(struct list_head *realloc_head,
>  		dev = add_res->dev;
>  		idx = pci_resource_num(dev, res);
>  
> +		/* Skip this resource if not found in head list */
> +		if (!res_to_dev_res(head, res))
> +			continue;
> +
>  		/*
>  		 * Skip resource that failed the earlier assignment and is
>  		 * not optional as it would just fail again.
> @@ -442,10 +446,6 @@ static void reassign_resources_sorted(struct list_head *realloc_head,
>  		    !pci_resource_is_optional(dev, idx))
>  			goto out;
>  
> -		/* Skip this resource if not found in head list */
> -		if (!res_to_dev_res(head, res))
> -			continue;
> -
>  		res_name = pci_resource_name(dev, idx);
>  		add_size = add_res->add_size;
>  		align = add_res->min_align;
> 
> base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
> -- 
> 2.39.5
>