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

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Date:   Tue, 18 Jun 2019 00:43:35 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Keith Busch <keith.busch@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Alexandru Gagniuc <mr.nuke.me@...il.com>
Subject: Re: [PATCH] PCI/PME: Fix race on PME polling

On Monday, June 17, 2019 4:53:48 PM CEST Lukas Wunner wrote:
> On Mon, Jun 17, 2019 at 05:35:10PM +0300, Mika Westerberg wrote:
> > Today when doing some PM testing I noticed that this patch actually
> > reveals an issue in our native PME handling. Problem is in
> > pcie_pme_handle_request() where we first convert req_id to struct
> > pci_dev and then call pci_check_pme_status() for it. Now, when a device
> > triggers wake the link is first brought up and then the PME is sent to
> > root complex with req_id matching the originating device. However, if
> > there are PCIe ports in the middle they may still be in D3 which means
> > that pci_check_pme_status() returns 0xffff for the device below so there
> > are lots of
> > 
> > 	Spurious native interrupt"
> > 
> > messages in the dmesg but the actual PME is never handled.
> > 
> > It has been working because pci_check_pme_status() returned true in case
> > of 0xffff as well and we went and runtime resumed to originating device.
> > 
> > I think the correct way to handle this is actually drop the call to
> > pci_check_pme_status() in pcie_pme_handle_request() because the whole
> > idea of req_id in PME message is to allow the root complex and SW to
> > identify the device without need to poll for the PME status bit.
> 
> Either that or the call to pci_check_pme_status() should be encapsulated
> in a pci_config_pm_runtime_get() / _put() pair.

And the whole hierarchy might as well be resumed, which could be rather
wasteful.

The problem is that the $subject patch should affect polling only, but it has
side effects beyond that.