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 This means that any previous atomic state we had before suspending is no longer valid, since it'll still be pointing to missing connectors.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.
Upstream fix: 0552f7651bc2 ("drm/i915/mst: use reference counted connectors. (v3)") Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Lyude cpaul@redhat.com --- 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 0104a06..6fdb90e 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -15958,6 +15958,18 @@ 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 && + state->num_connector != dev->mode_config.num_connector) { + drm_atomic_state_free(state); + state = NULL; + } + if (ret == 0 && !setup) { setup = true;