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SubjectRe: [PATCH] PCI/ASPM: Call pcie_aspm_sanity_check() as late as possible
[+cc Jan]

On Thu, Oct 06, 2022 at 01:59:50PM +0200, Stephen Kitt wrote:
> In pcie_aspm_init_link_state(), a number of checks are made to
> determine whether the function should proceed, before the result of
> the call to pcie_aspm_sanity_check() is actually used. The latter
> function doesn't change any state, it only reports a result, so
> calling it later doesn't make any difference to the state of the
> devices or the information we have about them. But having the call
> early reportedly can cause null-pointer dereferences; see
> https://unix.stackexchange.com/q/322337 for one example with
> pcie_aspm=off (this was reported in 2016, but the relevant code hasn't
> changed since then).

Thanks, Stephen!

That stackexchange report doesn't have much information, but it looks
similar to this old report from Jan Rueth, which I'm sorry to say I
never got resolved:

https://bugzilla.kernel.org/show_bug.cgi?id=187731
https://lore.kernel.org/all/4cec62c2-218a-672b-8c12-d44e8df56aae@comsys.rwth-aachen.de/#t

And Jan's patch is almost identical to yours :)

I hope to get this resolved, but I don't have time to work on it
before the upcoming merge window, which will probably open Sunday.
And then it's holiday time, so it may be January before I get back to
it. I'm just dropping the links here as breadcrumbs for picking this
back up.

Bjorn

> This moves the call to pcie_aspm_sanity_check() just before the result
> is actually used, giving all the other checks a chance to run first.
>
> Signed-off-by: Stephen Kitt <steve@sk2.org>
> ---
> drivers/pci/pcie/aspm.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
> index a8aec190986c..38df439568b7 100644
> --- a/drivers/pci/pcie/aspm.c
> +++ b/drivers/pci/pcie/aspm.c
> @@ -889,7 +889,7 @@ static void pcie_aspm_update_sysfs_visibility(struct pci_dev *pdev)
> void pcie_aspm_init_link_state(struct pci_dev *pdev)
> {
> struct pcie_link_state *link;
> - int blacklist = !!pcie_aspm_sanity_check(pdev);
> + int blacklist;
>
> if (!aspm_support_enabled)
> return;
> @@ -923,6 +923,7 @@ void pcie_aspm_init_link_state(struct pci_dev *pdev)
> * upstream links also because capable state of them can be
> * update through pcie_aspm_cap_init().
> */
> + blacklist = !!pcie_aspm_sanity_check(pdev);
> pcie_aspm_cap_init(link, blacklist);
>
> /* Setup initial Clock PM state */
>
> base-commit: 833477fce7a14d43ae4c07f8ddc32fa5119471a2
> --
> 2.30.2
>

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