Re: [PATCH] PCI: check bridge->bus in pci_host_common_remove

[Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>]

On Mon, Oct 28, 2024 at 04:46:43PM +0800, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@nxp.com>
> 
> When PCI node was created using an overlay and the overlay is
> reverted/destroyed, the "linux,pci-domain" property no longer exists,
> so of_get_pci_domain_nr will return failure. Then
> of_pci_bus_release_domain_nr will actually use the dynamic IDA, even
> if the IDA was allocated in static IDA. So the flow is as below:
> A: of_changeset_revert
>     pci_host_common_remove
>      pci_bus_release_domain_nr
>        of_pci_bus_release_domain_nr
>          of_get_pci_domain_nr      # fails because overlay is gone
>          ida_free(&pci_domain_nr_dynamic_ida)
> 
> With driver calls pci_host_common_remove explicity, the flow becomes:
> B pci_host_common_remove
>    pci_bus_release_domain_nr
>     of_pci_bus_release_domain_nr
>      of_get_pci_domain_nr      # succeeds in this order
>       ida_free(&pci_domain_nr_static_ida)
> A of_changeset_revert
>    pci_host_common_remove
> 
> With updated flow, the pci_host_common_remove will be called twice,
> so need to check 'bridge->bus' to avoid accessing invalid pointer.
> 
> Fixes: c14f7ccc9f5d ("PCI: Assign PCI domain IDs by ida_alloc()")
> Signed-off-by: Peng Fan <peng.fan@nxp.com>

I went through the previous discussion [1] and I couldn't see an agreement on
the point raised by Bjorn on 'removing the host bridge before the overlay'.

I do think this is a valid point and if you do not think so, please state the
reason.

- Mani

[1] https://lore.kernel.org/lkml/20230913115737.GA426735@bhelgaas/

> ---
> 
> V1:
>  Not sure to keep the fixes here. I could drop the Fixes tag if it is
>  improper.
>  This is to revisit the patch [1] which was rejected last year. This
>  new flow is using the suggest flow following Bjorn's suggestion.
>  But of_changeset_revert will still invoke plaform_remove and then
>  pci_host_common_remove. So worked out this patch together with a patch
>  to jailhouse driver as below:
>  static void destroy_vpci_of_overlay(void)
>  {
> +       struct device_node *vpci_node = NULL;
> +
>         if (overlay_applied) {
> +#if LINUX_VERSION_CODE >= KERNEL_VERSION(6,6,0)
> +               vpci_node = of_find_node_by_path("/pci@0");
> +               if (vpci_node) {
> +                       struct platform_device *pdev = of_find_device_by_node(vpci_node);
> +                       if (!pdev)
> +                               printk("Not found device for /pci@0\n");
> +                       else {
> +                               pci_host_common_remove(pdev);
> +                               platform_device_put(pdev);
> +                       }
> +               }
> +               of_node_put(vpci_node);
> +#endif
> +
>                 of_changeset_revert(&overlay_changeset);
> 
>  [1] https://lore.kernel.org/lkml/20230908224858.GA306960@bhelgaas/T/#md12e6097d91a012ede78c997fc5abf460029a569
> 
>  drivers/pci/controller/pci-host-common.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/controller/pci-host-common.c b/drivers/pci/controller/pci-host-common.c
> index cf5f59a745b3..5a9c29fc57cd 100644
> --- a/drivers/pci/controller/pci-host-common.c
> +++ b/drivers/pci/controller/pci-host-common.c
> @@ -86,8 +86,10 @@ void pci_host_common_remove(struct platform_device *pdev)
>  	struct pci_host_bridge *bridge = platform_get_drvdata(pdev);
>  
>  	pci_lock_rescan_remove();
> -	pci_stop_root_bus(bridge->bus);
> -	pci_remove_root_bus(bridge->bus);
> +	if (bridge->bus) {
> +		pci_stop_root_bus(bridge->bus);
> +		pci_remove_root_bus(bridge->bus);
> +	}
>  	pci_unlock_rescan_remove();
>  }
>  EXPORT_SYMBOL_GPL(pci_host_common_remove);
> -- 
> 2.37.1
> 

-- 
மணிவண்ணன் சதாசிவம்