[PATCH v2] drm/i915: Discard previous atomic state on resume if connectors change

[Daniel Vetter]

On Mon, May 09, 2016 at 10:07:08AM -0400, Lyude Paul wrote:
> Yep, Dave's patches fix the issue on their own so this is only going to be
> needed for 4.6.

Ok, so not the first one that only needs to be applied to stable kernels.
For that to work you need to explain that this is the most minimal fix for
stabel kernels, and add a reference to the final commit in upstream that
fixes the issue for real. Otherwise Greg KH won't take it. It still needs
my ack.

Probably best to have an entire dp mst series for all of those, but maybe
ping me first on irc so I can check them quickly before you hit send.
-Daniel

> 
> On Mon, 2016-05-09 at 08:42 +0200, Daniel Vetter wrote:
> > On Fri, May 06, 2016 at 05:39:56PM -0400, Lyude wrote:
> > > 
> > > If an MST device is disconnected while the machine is suspended, the
> > > number of connectors will change as well after we call
> > > intel_dp_mst_resume(). This means that any previous atomic state we had
> > > before suspending is no longer valid, since it'll still be pointing to
> > > missing connectors. We need to check for this before committing the
> > > state, otherwise we'll kernel panic on resume whenever if any MST
> > > display was disconnected before we started resuming:
> > > 
> > > BUG: unable to handle kernel NULL pointer dereference at 0000000000000008
> > > IP: [<ffffffffa01588ef>] drm_atomic_helper_check_modeset+0x29f/0xb40
> > > [drm_kms_helper]
> > > Call Trace:
> > >  [<ffffffffa02354f4>] intel_atomic_check+0x34/0x1180 [i915]
> > >  [<ffffffff810e6c3f>] ? mark_held_locks+0x6f/0xa0
> > >  [<ffffffff810e6d99>] ? trace_hardirqs_on_caller+0x129/0x1b0
> > >  [<ffffffffa00ff1d2>] drm_atomic_check_only+0x192/0x620 [drm]
> > >  [<ffffffff813ee001>] ? pci_pm_thaw+0x21/0x90
> > >  [<ffffffffa00ff677>] drm_atomic_commit+0x17/0x60 [drm]
> > >  [<ffffffffa023e0ad>] intel_display_resume+0xbd/0x160 [i915]
> > >  [<ffffffff813ee070>] ? pci_pm_thaw+0x90/0x90
> > >  [<ffffffffa01b60d8>] i915_drm_resume+0xd8/0x160 [i915]
> > >  [<ffffffffa01b6185>] i915_pm_resume+0x25/0x30 [i915]
> > >  [<ffffffff813ee0d4>] pci_pm_resume+0x64/0xa0
> > >  [<ffffffff814d9ea0>] dpm_run_callback+0x90/0x190
> > >  [<ffffffff814da455>] device_resume+0xd5/0x1f0
> > >  [<ffffffff814da58d>] async_resume+0x1d/0x50
> > >  [<ffffffff810b6718>] async_run_entry_fn+0x48/0x150
> > >  [<ffffffff810acc19>] process_one_work+0x1e9/0x5c0
> > >  [<ffffffff810acb96>] ? process_one_work+0x166/0x5c0
> > >  [<ffffffff810ad038>] worker_thread+0x48/0x4e0
> > >  [<ffffffff810acff0>] ? process_one_work+0x5c0/0x5c0
> > >  [<ffffffff810b3794>] kthread+0xe4/0x100
> > >  [<ffffffff81742672>] ret_from_fork+0x22/0x50
> > >  [<ffffffff810b36b0>] ? kthread_create_on_node+0x200/0x200
> > > 
> > > Changes since v1:
> > >   - Move drm_atomic_state_free() call down so we're holding the
> > >     appropriate locks when destroying the atomic state
> > > 
> > > Cc: stable at vger.kernel.org
> > > Signed-off-by: Lyude <cpaul at redhat.com>
> > Is this still an issue on -nightly with the connector refcounting fixed?
> > -Daniel
> > 
> > > 
> > > ---
> > >  drivers/gpu/drm/i915/intel_display.c | 12 ++++++++++++
> > >  1 file changed, 12 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/intel_display.c
> > > b/drivers/gpu/drm/i915/intel_display.c
> > > index 0f29ef6..d68efc7 100644
> > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > @@ -15934,6 +15934,18 @@ void intel_display_resume(struct drm_device *dev)
> > >  retry:
> > >  	ret = drm_modeset_lock_all_ctx(dev, &ctx);
> > >  
> > > +	/*
> > > +	 * With MST, the number of connectors can change between suspend
> > > and
> > > +	 * resume, which means that the state we want to restore might now
> > > be
> > > +	 * impossible to use since it'll be pointing to non-existant
> > > +	 * connectors.
> > > +	 */
> > > +	if (ret == 0 &&
> > > +	    state->num_connector != dev->mode_config.num_connector) {
> > > +		drm_atomic_state_free(state);
> > > +		state = NULL;
> > > +	}
> > > +
> > >  	if (ret == 0 && !setup) {
> > >  		setup = true;
> > >  
> > > -- 
> > > 2.5.5
> > > 
> > > _______________________________________________
> > > dri-devel mailing list
> > > dri-devel at lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> -- 
> Cheers,
> 	Lyude
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch