Bug 79051

Happens usually within first minute of starting weston (drm on archlinux.) just opening windows and moving mouse. (no panic within X.)

Bisected to
https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-3.14.y&id=19aef29eea6e5b42e4097c2ccdd80e944e9f9f6f

Still same with 3.16-rc2.

Panic only dumped to screen so don't have exact copy.
RIP in drm_vblank_put
radeon_crt_handle_flip
evergreen_irq_process
notice_schd_clock
radeon_irq_handler_kms
handle_irq_events_percpu
...

Removing the one line stops the panic so does this;

diff --git a/drivers/gpu/drm/radeon/evergreen.c b/drivers/gpu/drm/radeon/evergre
index 971d933..e31d936 100644
--- a/drivers/gpu/drm/radeon/evergreen.c
+++ b/drivers/gpu/drm/radeon/evergreen.c
@@ -4967,7 +4967,8 @@ restart_ih:
                case 16: /* D5 page flip */
                case 18: /* D6 page flip */
                        DRM_DEBUG("IH: D%d flip\n", ((src_id - 8) >> 1) + 1);
-                       radeon_crtc_handle_flip(rdev, (src_id - 8) >> 1);
+                       if (atomic_read(&rdev->irq.pflip[(src_id - 8) >> 1]))
+                               radeon_crtc_handle_flip(rdev, (src_id - 8) >> 1)
                        break;
                case 42: /* HPD hotplug */
                        switch (src_data) {

Only guess work on my part. Needs someone with knowledge of code determine real fix.