Re: Panic after S3 resume and modeset with MST

Takashi Iwai
2017-03-30T18:50:08Z

On Thu, 30 Mar 2017 20:07:42 +0200,
Lyude Paul wrote:
>
> On Thu, 2017-03-30 at 07:55 +0200, Takashi Iwai wrote:
> > On Thu, 30 Mar 2017 02:24:37 +0200,
> > Lyude Paul wrote:
> > >
> > > On Wed, 2017-03-29 at 15:54 +0200, Takashi Iwai wrote:
> > > > On Wed, 29 Mar 2017 15:34:15 +0200,
> > > > Ville Syrjälä wrote:
> > > > >
> > > > > On Wed, Mar 29, 2017 at 03:10:09PM +0200, Takashi Iwai wrote:
> > > > > > On Mon, 27 Mar 2017 18:02:13 +0200,
> > > > > > Takashi Iwai wrote:
> > > > > > >
> > > > > > > Hi,
> > > > > > >
> > > > > > > the upstream fix a16b7658f4e0d4aec9bc3e75a5f0cc3f7a3a0422
> > > > > > >     drm/i915: Call intel_dp_mst_resume() before resuming
> > > > > > > displays
> > > > > > >
> > > > > > > seems to trigger a kernel panic when some modeset change
> > > > > > > happens after
> > > > > > > S3 resume.  The details are found in openSUSE bugzilla,
> > > > > > >   https://bugzilla.suse.com/show_bug.cgi?id=1029634
> > > > > > >
> > > > > > > In short, the following procedure causes a kernel panic
> > > > > > > (supposedly)
> > > > > > > almost 100% on Dell Latitude with Skylake with MST DP on
> > > > > > > dock:
> > > > > > >
> > > > > > > - Boot with a docking station, DP-1 connected.
> > > > > > > - Login on X
> > > > > > > - xrandr --output eDP-1 --primary --auto --output DP-1-1 --
> > > > > > > auto
> > > > > > > --left-of eDP-1
> > > > > > >   ==> This changes the mode.
> > > > > > > - Suspend ("systemctl suspend" in my case), and close the
> > > > > > > lid.
> > > > > > > - Remove from the dock (keep the lid closed).
> > > > > > > - Open the lid, which resumes automatically.  It works.
> > > > > > > - Suspend again.
> > > > > > > - Connect to the dock again (keep the lid closed).
> > > > > > > - Open the lid, which resumes automatically.  It's still
> > > > > > > OK.
> > > > > > > - xrandr --output eDP-1 --primary --auto --output DP-1-1 --
> > > > > > > auto
> > > > > > > --left-of eDP-1
> > > > > > >   ==> Now the kernel feezes.
> > > > > > >
> > > > > > > Reverting the commit mentioned above fixes the problem.
> > > > > > >
> > > > > > > The problem is present in all versions I tested.  The
> > > > > > > reported
> > > > > > > kernel
> > > > > > > in the Bugzilla is 4.4.x-based one, but the issue is seen
> > > > > > > in
> > > > > > > 4.11-rc3,
> > > > > > > too.  Note that the S3 resume itself works in 4.11-rc3; the
> > > > > > > kernel
> > > > > > > panic happens when invoking xrandr manually after that.
> > > > > > >
> > > > > > > Unfortunately, I couldn't get a kernel panic message, so
> > > > > > > far.  kdump
> > > > > > > didn't work well in this case by some reason.  There are
> > > > > > > some
> > > > > > > screenshots taken by the original reporter (could switch VT
> > > > > > > beforehand), but I don't know whether it helps.
> > > > > > >
> > > > > > > If you have any hints for further debugging, it'd be highly
> > > > > > > appreciated.
> > > > > >
> > > > > > It seems that the patch below works around the problem.
> > > > > > Can anyone enlighten what's going on there?
> > > > > >
> > > > > >
> > > > > > thanks,
> > > > > >
> > > > > > Takashi
> > > > > >
> > > > > > -- 8< --
> > > > > > From: Takashi Iwai <tiwai@suse.de>
> > > > > > Subject: [PATCH] drm/i915: Fix crash after S3 resume with DP
> > > > > > MST
> > > > > > mode change
> > > > > >
> > > > > > We've got a bug report showing that Skylake Dell machines
> > > > > > with a
> > > > > > docking station causes a kernel panic after S3 resume and
> > > > > > modeset.
> > > > > > The details are found in the openSUSE bugzilla entry
> > > > > > below.  The
> > > > > > typical test procedure is:
> > > > > >
> > > > > > - Laptop is Dell Latitude with eDP (1366x768)
> > > > > > - Boot with docking station connected to a DP (1920x1080)
> > > > > > - Login, change the mode via
> > > > > >   xrandr --output eDP-1 --auto --output DP-1-1 --auto --left-
> > > > > > of
> > > > > > eDP-1
> > > > > > - Suspend, and close the lid after the suspend
> > > > > >   (or close the lid to trigger the suspend)
> > > > > > - Undock while keeping the lid closed.
> > > > > > - Open the lid, which triggers the resume;
> > > > > >   the machine wakes up well, and X shows up.  No problem, so
> > > > > > far.
> > > > > > - Suspend again, close the lid.
> > > > > > - Dock again while keeping the lid closed.
> > > > > > - Open the lid, triggering the resume; this wakes up still
> > > > > > fine.
> > > > > > - At this moment, run xrandr again to re-setup DP-1
> > > > > >   xrandr --output eDP-1 --auto --output DP-1-1 --auto --left-
> > > > > > of
> > > > > > eDP-1
> > > > > >   ==> This triggers a hard crash.
> > > > > >
> > > > > > I could bisect it, and this leaded to the commit a16b7658f4e0
> > > > > > ("drm/i915: Call intel_dp_mst_resume() before resuming
> > > > > > displays").
> > > > > >
> > > > > > Basically the commit just shuffles the calls of
> > > > > > intel_display_resume()
> > > > > > and intel_dp_mst_resume().  So as a workaround, I tried to
> > > > > > split
> > > > > > intel_dp_mst_resume() call to postpone the suspected code
> > > > > > (the
> > > > > > invocation of intel_dp_check_mst_status()), then bingo, this
> > > > > > cured the
> > > > > > problem.
> > > > > >
> > > > > > But don't ask me *why* this fixes.  It's still in a cargo-
> > > > > > cult
> > > > > > state.
> > > > > >
> > > > > > Fixes: a16b7658f4e0 ("drm/i915: Call intel_dp_mst_resume()
> > > > > > before
> > > > > > resuming displays")
> > > > > > Bugzilla: https://bugzilla.suse.com/show_bug.cgi?id=1029634
> > > > > > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > > > > > ---
> > > > > >  drivers/gpu/drm/i915/i915_drv.c  |  5 ++++-
> > > > > >  drivers/gpu/drm/i915/intel_dp.c  | 20 +++++++++++++++++++-
> > > > > >  drivers/gpu/drm/i915/intel_drv.h |  3 ++-
> > > > > >  3 files changed, 25 insertions(+), 3 deletions(-)
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/i915/i915_drv.c
> > > > > > b/drivers/gpu/drm/i915/i915_drv.c
> > > > > > index 1c75402a59c1..62c40090ceed 100644
> > > > > > --- a/drivers/gpu/drm/i915/i915_drv.c
> > > > > > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > > > > > @@ -1559,6 +1559,7 @@ static int
> > > > > > i915_suspend_switcheroo(struct
> > > > > > drm_device *dev, pm_message_t state)
> > > > > >  static int i915_drm_resume(struct drm_device *dev)
> > > > > >  {
> > > > > >   struct drm_i915_private *dev_priv = to_i915(dev);
> > > > > > + int mst_pending;
> > > > > >   int ret;
> > > > > >
> > > > > >   disable_rpm_wakeref_asserts(dev_priv);
> > > > > > @@ -1608,10 +1609,12 @@ static int i915_drm_resume(struct
> > > > > > drm_device *dev)
> > > > > >   dev_priv->display.hpd_irq_setup(dev_priv);
> > > > > >   spin_unlock_irq(&dev_priv->irq_lock);
> > > > > >
> > > > > > - intel_dp_mst_resume(dev);
> > > > > > + mst_pending = intel_dp_mst_resume(dev);
> > > > > >
> > > > > >   intel_display_resume(dev);
> > > > > >
> > > > > > + intel_dp_mst_resume_post(dev, mst_pending);
> > > > > > +
> > > > > >   drm_kms_helper_poll_enable(dev);
> > > > > >
> > > > > >   /*
> > > > > > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > > > > > b/drivers/gpu/drm/i915/intel_dp.c
> > > > > > index d1670b8afbf5..fc5ea900e6f3 100644
> > > > > > --- a/drivers/gpu/drm/i915/intel_dp.c
> > > > > > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > > > > > @@ -6027,9 +6027,10 @@ void intel_dp_mst_suspend(struct
> > > > > > drm_device *dev)
> > > > > >   }
> > > > > >  }
> > > > > >
> > > > > > -void intel_dp_mst_resume(struct drm_device *dev)
> > > > > > +int intel_dp_mst_resume(struct drm_device *dev)
> > > > > >  {
> > > > > >   struct drm_i915_private *dev_priv = to_i915(dev);
> > > > > > + int pending = 0;
> > > > > >   int i;
> > > > > >
> > > > > >   for (i = 0; i < I915_MAX_PORTS; i++) {
> > > > > > @@ -6041,6 +6042,23 @@ void intel_dp_mst_resume(struct
> > > > > > drm_device
> > > > > > *dev)
> > > > > >
> > > > > >   ret =
> > > > > > drm_dp_mst_topology_mgr_resume(&intel_dig_port->dp.mst_mgr);
> > > > > >   if (ret)
> > > > > > + pending |= 1 << i;
> > > > > > + }
> > > > > > +
> > > > > > + return pending;
> > > > > > +}
> > > > > > +
> > > > > > +void intel_dp_mst_resume_post(struct drm_device *dev, int
> > > > > > pending)
> > > > > > +{
> > > > > > + struct drm_i915_private *dev_priv = to_i915(dev);
> > > > > > + int i;
> > > > > > +
> > > > > > + for (i = 0; i < I915_MAX_PORTS; i++) {
> > > > > > + struct intel_digital_port *intel_dig_port =
> > > > > > + dev_priv->hotplug.irq_port[i];
> > > > > > + if (!intel_dig_port || !intel_dig_port-
> > > > > > > dp.can_mst)
> > > > > >
> > > > > > + continue;
> > > > > > + if (pending & (1 << i))
> > > > > >   intel_dp_check_mst_status(&intel_dig
> > > > > > _por
> > > > > > t->dp);
> > > > > >   }
> > > > > >  }
> > > > >
> > > > > The whole MST resume is a bit of chicken and egg type of
> > > > > situation.
> > > > > We
> > > > > need the HPD interrupts to resume the previous state, but we
> > > > > don't
> > > > > want
> > > > > to actually process real hotplugs until we've done the resume.
> > > > > The
> > > > > current code is definitely broken IMO.
> > > > >
> > > > > But I'm not really sure why this patch fixes things because the
> > > > > HPD
> > > > > processing that will occur when we talk to the sink during the
> > > > > display
> > > > > resume should also call intel_dp_check_mst_status().
> > > >
> > > > Actually, just dropping intel_dp_check_mst_status() calls in
> > > > intel_dp_mst_resume() seems enough to fix the problem.
> > > >
> > > > Below is the v2 patch doing that.  Does it make more sense?
> > >
> > > Barely, unfortunately :(. I'll be honest I'm a little surprised
> > > this
> > > patch doesn't break anything, but you do seem to be right in saying
> > > that hotplugging re-sets up the displays in the event that things
> > > go
> > > wrong.
> > >
> > > Going through the backtrace and the dmesg that you gave on the
> > > bugzilla
> > > I can't figure out any definitive answer for why this is crashing.
> > > We
> > > will have to get dmesg output from when it crashes to understand
> > > this
> > > I'm pretty sure.
> > >
> > > JFYI (I really need to make a guide for this somewhere...) I
> > > usually
> > > use the netconsole module to get kernel output from machines when
> > > they
> > > kernel panic. In your case I would set this up right before you do
> > > the
> > > final `xrandr` call that kills the machine, since netconsole has
> > > not
> > > been very reliable in my experience over suspend/resume cycles. It
> > > might take a few tries to get it to print the whole crash to the
> > > netconsole (and you will need to make sure the system has a PCI
> > > ethernet adapter, USB or wifi won't do), but this usually works.
> >
> > I've already tried netconsole (even before kdump), but unfortunately
> > it doesn't work in this case.  As mentioned in Bugzilla, the network
> > goes crazy when the machine crashes (even the whole network segment
> > the machine connects to is stalling).  It's similar like the symptom
> > we've seen with the SKL CPU-state screw up in the past with
> > intel_idle
> > driver.
> Do you think you might be able to get a translation of the stack dump
> to the actual lines this issues is occurring on? You should be able to
> do this against i915.ko using eu-addr2line (it will have to be against
> the same kernel build you're running on the crashing machine, hence why
> I can't just do it myself). I might see if I can give you some patches
> to spit some info out.

Sure, if we get a proper stack dump, we can analyze it somehow. You
can use addr2line, or even check objdump output manually.
But in this case, as already mentioned, it was impossible to get any
sensible stack trace on my machine with 4.11-rc, so far,
unfortunately. So no material to read.

That is, the problem isn't how to translate it, but how to get it.
Normal ways didn't work. Maybe I can try AMT, but I doubt that it'll
give any output since kdump already failed...

thanks,