linux-kernel - Re: [PATCH] PCI: check bridge->bus in pci_host_common

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Message-ID: <20241119174931.GA2270058@bhelgaas>
Date: Tue, 19 Nov 2024 11:49:31 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: "Peng Fan (OSS)" <peng.fan@....nxp.com>
Cc: Will Deacon <will@...nel.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Pali Rohár <pali@...nel.org>,
	"open list:PCI DRIVER FOR GENERIC OF HOSTS" <linux-pci@...r.kernel.org>,
	"moderated list:PCI DRIVER FOR GENERIC OF HOSTS" <linux-arm-kernel@...ts.infradead.org>,
	open list <linux-kernel@...r.kernel.org>,
	Peng Fan <peng.fan@....com>
Subject: Re: [PATCH] PCI: check bridge->bus in pci_host_common_remove

On Mon, Oct 28, 2024 at 04:46:43PM +0800, Peng Fan (OSS) wrote:
> From: Peng Fan <peng.fan@....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.

If/when you post a v2 of this, please:

  - Update the subject to say *why* this change is desirable.

  - Follow the capitalization convention (use "git log --oneline" to
    discover it).

  - Add "()" after function names in the text (no need in the call
    tree because that's obviously all functions).

  - Mention the user-visible problem this fixes, e.g., do you see an
    oops because of a NULL pointer dereference?