Re: [PATCH] PCI/PME: Fix race on PME polling

[Rafael J. Wysocki]

On Sunday, June 9, 2019 1:29:33 PM CEST Lukas Wunner wrote:
> Since commit df17e62e5bff ("PCI: Add support for polling PME state on
> suspended legacy PCI devices"), the work item pci_pme_list_scan() polls
> the PME status flag of devices and wakes them up if the bit is set.
> 
> The function performs a check whether a device's upstream bridge is in
> D0 for otherwise the device is inaccessible, rendering PME polling
> impossible.  However the check is racy because it is performed before
> polling the device.  If the upstream bridge runtime suspends to D3hot
> after pci_pme_list_scan() checks its power state and before it invokes
> pci_pme_wakeup(), the latter will read the PMCSR as "all ones" and
> mistake it for a set PME status flag.  I am seeing this race play out as
> a Thunderbolt controller going to D3cold and occasionally immediately
> going to D0 again because PM polling was performed at just the wrong
> time.
> 
> Avoid by checking for an "all ones" PMCSR in pci_check_pme_status().
> 
> Fixes: 58ff463396ad ("PCI PM: Add function for checking PME status of devices")
> Tested-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> Signed-off-by: Lukas Wunner <lukas@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx # v2.6.34+
> Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> ---
>  drivers/pci/pci.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 8abc843b1615..eed5db9f152f 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -1989,6 +1989,8 @@ bool pci_check_pme_status(struct pci_dev *dev)
>  	pci_read_config_word(dev, pmcsr_pos, &pmcsr);
>  	if (!(pmcsr & PCI_PM_CTRL_PME_STATUS))
>  		return false;
> +	if (pmcsr == 0xffff)
> +		return false;
>  
>  	/* Clear PME status. */
>  	pmcsr |= PCI_PM_CTRL_PME_STATUS;
> 

Added to my 5.3 queue, thanks!