On Tue, Jan 23, 2024 at 11:55:31AM -0700, Alex Williamson wrote:
> The commit noted in fixes added a bogus requirement that runtime PM
> managed devices need to be in the RPM_ACTIVE state for PME polling.
> In fact, only devices in low power states should be polled.
>
> However there's still a requirement that the device config space must
> be accessible, which has implications for both the current state of
> the polled device and the parent bridge, when present. It's not
> sufficient to assume the bridge remains in D0 and cases have been
> observed where the bridge passes the D0 test, but the PM state
> indicates RPM_SUSPENDING and config space of the polled device becomes
> inaccessible during pci_pme_wakeup().
>
> Therefore, since the bridge is already effectively required to be in
> the RPM_ACTIVE state, formalize this in the code and elevate the PM
> usage count to maintain the state while polling the subordinate
> device.
This apparently fixes a problem: the bugzilla says something about
disks attached to Thunderbolt/USB4 docks not working, but I doubt it's
actually specific to Thunderbolt/USB4 or to disks.
The bugzilla also indicates that d3fcd7360338 was a regression.
d3fcd7360338 appeared in v6.6, so this fix is likely a candidate for
the current release (v6.8).
I'd like to mention both the user-visible problem being fixed and
the fact that it fixes a regression here in the commit log so we can
make the case for putting this in v6.8.
> Cc: Lukas Wunner <lukas@xxxxxxxxx>
> Cc: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> Cc: Rafael J. Wysocki <rafael@xxxxxxxxxx>
> Fixes: d3fcd7360338 ("PCI: Fix runtime PM race with PME polling")
> Reported-by: Sanath S <sanath.s@xxxxxxx>
> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218360
> Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx>
> ---
> drivers/pci/pci.c | 37 ++++++++++++++++++++++---------------
> 1 file changed, 22 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index bdbf8a94b4d0..764d7c977ef4 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2433,29 +2433,36 @@ static void pci_pme_list_scan(struct work_struct *work)
> if (pdev->pme_poll) {
> struct pci_dev *bridge = pdev->bus->self;
> struct device *dev = &pdev->dev;
> - int pm_status;
> + struct device *bdev = bridge ? &bridge->dev : NULL;
> + int bref = 0;
>
> /*
> - * If bridge is in low power state, the
> - * configuration space of subordinate devices
> - * may be not accessible
> + * If we have a bridge, it should be in an active/D0
> + * state or the configuration space of subordinate
> + * devices may not be accessible or stable over the
> + * course of the call.
> */
> - if (bridge && bridge->current_state != PCI_D0)
> - continue;
> + if (bdev) {
> + bref = pm_runtime_get_if_active(bdev, true);
> + if (!bref)
> + continue;
> +
> + if (bridge->current_state != PCI_D0)
> + goto put_bridge;
> + }
>
> /*
> - * If the device is in a low power state it
> - * should not be polled either.
> + * The device itself should be suspended but config
> + * space must be accessible, therefore it cannot be in
> + * D3cold.
> */
> - pm_status = pm_runtime_get_if_active(dev, true);
> - if (!pm_status)
> - continue;
> -
> - if (pdev->current_state != PCI_D3cold)
> + if (pm_runtime_suspended(dev) &&
> + pdev->current_state != PCI_D3cold)
> pci_pme_wakeup(pdev, NULL);
>
> - if (pm_status > 0)
> - pm_runtime_put(dev);
> +put_bridge:
> + if (bref > 0)
> + pm_runtime_put(bdev);
> } else {
> list_del(&pme_dev->list);
> kfree(pme_dev);
> --
> 2.43.0
>
