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

From: Lukas Wunner <lukas@wunner.de>
To: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Bjorn Helgaas <bhelgaas@google.com>,
	linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	Keith Busch <keith.busch@intel.com>,
	Alex Williamson <alex.williamson@redhat.com>,
	Alexandru Gagniuc <mr.nuke.me@gmail.com>
Subject: Re: [PATCH] PCI/PME: Fix race on PME polling
Date: Mon, 17 Jun 2019 16:53:48 +0200	[thread overview]
Message-ID: <20190617145348.cqmtuqlvabgpo2ky@wunner.de> (raw)
In-Reply-To: <20190617143510.GT2640@lahna.fi.intel.com>

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.

Thanks,

Lukas