linux-kernel - Re: [PATCH v2] PCI/PM: Avoid suspending the device with errors

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Message-ID: <CAJZ5v0ifgqzqP8N+NXJ=UVZ434SiyzgZjn1EuWy4HTT4TKOGWg@mail.gmail.com>
Date: Thu, 24 Apr 2025 12:59:55 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Raag Jadav <raag.jadav@...el.com>
Cc: Bjorn Helgaas <helgaas@...nel.org>, rafael@...nel.org, mahesh@...ux.ibm.com, 
	oohall@...il.com, bhelgaas@...gle.com, linux-pci@...r.kernel.org, 
	linux-kernel@...r.kernel.org, ilpo.jarvinen@...ux.intel.com, lukas@...ner.de, 
	aravind.iddamsetty@...ux.intel.com
Subject: Re: [PATCH v2] PCI/PM: Avoid suspending the device with errors

On Thu, Apr 24, 2025 at 7:12 AM Raag Jadav <raag.jadav@...el.com> wrote:
>
> On Tue, Apr 22, 2025 at 02:45:37PM -0500, Bjorn Helgaas wrote:
> > On Tue, Apr 22, 2025 at 07:23:41PM +0530, Raag Jadav wrote:
> > > If an error is triggered before or during system suspend, any bus level
> > > power state transition will result in unpredictable behaviour by the
> > > device with failed recovery. Avoid suspending such a device and leave
> > > it in its existing power state.
> > >
> > > This only covers the devices that rely on PCI core PM for their power
> > > state transition.
> > >
> > > Signed-off-by: Raag Jadav <raag.jadav@...el.com>
> > > ---
> > >
> > > v2: Synchronize AER handling with PCI PM (Rafael)
> > >
> > > More discussion on [1].
> > > [1] https://lore.kernel.org/all/CAJZ5v0g-aJXfVH+Uc=9eRPuW08t-6PwzdyMXsC6FZRKYJtY03Q@mail.gmail.com/
> >
> > Thanks for the pointer, but the commit log for this patch needs to be
> > complete in itself.  "Unpredictable behavior" is kind of hand-wavy and
> > doesn't really help understand the problem.
> >
> > >  drivers/pci/pci-driver.c |  3 ++-
> > >  drivers/pci/pcie/aer.c   | 11 +++++++++++
> > >  include/linux/aer.h      |  2 ++
> > >  3 files changed, 15 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c
> > > index f57ea36d125d..289a1fa7cb2d 100644
> > > --- a/drivers/pci/pci-driver.c
> > > +++ b/drivers/pci/pci-driver.c
> > > @@ -884,7 +884,8 @@ static int pci_pm_suspend_noirq(struct device *dev)
> > >             }
> > >     }
> > >
> > > -   if (!pci_dev->state_saved) {
> > > +   /* Avoid suspending the device with errors */
> > > +   if (!pci_aer_in_progress(pci_dev) && !pci_dev->state_saved) {
> >
> > This looks potentially racy, since hardware can set bits in
> > PCI_EXP_DEVSTA at any time.
>
> Which is why it's placed in ->suspend_noirq() callback. Can it still race?

With the hardware?  Yes.