Re: [PATCH 3/4] drm/i915: Discard previous atomic state on resume if connectors change

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Tue, May 31, 2016 at 12:49:06PM -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 before suspending is no longer valid, since it'll still be pointing to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
> Changes since v2:
>   - Check that state != NULL before we start accessing it's members
> 
> This fix is only required for 4.6 and below. David Airlie's patchseries
> for 4.7 to add connector reference counting provides a more proper fix
> for this.

This doesn't apply to 4.5-stable or 4.4-stable, if you want it there,
can you provide a backported version for me to apply?

thanks,

greg k-h