(About 30 OSADL QA Farm systems are now running 3.18.9-rt4. BTW: To check out what kernels are under test you may sort the kernel list (https://www.osadl.org/?id=933) by kernel version (https://www.osadl.org/?id=1001) and scroll down the page.)
The most striking problem of kernel 3.18.9-rt4 affects all systems that are equipped with Radeon graphics (irrespective whether PCIe cards or APUs with on-chip graphics). They suffer from a hanging radeon driver. The block occurs when accelerated graphics load is created by x11perf or gltestperf. Sometimes only the graphics are frozen while ssh login still is possible, somtimes the entire box is no longer accessible at all. In any case, a reboot is needed to recover from this situation.
Here is a selection of kernel messages:
Rack #0/Slot #3 [AMD/ATI] RV730 XT [Radeon HD 4670]: [16081.272035] INFO: task kworker/u24:4:268 blocked for more than 120 seconds. [16081.285776] Not tainted 3.18.9-rt4 #26 [16081.294286] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [16081.309901] kworker/u24:4 D ffff88081ed8b340 0 268 2 0x10000000 [16081.309938] Workqueue: radeon-crtc radeon_flip_work_func [radeon] [16081.309960] ffff880805ccfbe8 0000000000000046 ffff88081ed0c700 0000000000000000 [16081.309962] 0000000000009000 000000000000c920 ffff8808112fb420 ffff880805cc1a10 [16081.309963] ffff880805ccfbf8 000001008108a0da ffff880805ccfc98 ffff880805cc1a10 [16081.309966] Call Trace: [16081.309972] [<ffffffff81721ce4>] schedule+0x34/0xa0 [16081.309974] [<ffffffff8172425c>] schedule_timeout+0x22c/0x2d0 [16081.309984] [<ffffffffa046ca86>] ? radeon_fence_process+0x16/0x40 [radeon] [16081.309993] [<ffffffffa046caf4>] ? radeon_fence_any_seq_signaled+0x44/0x90 [radeon] [16081.310001] [<ffffffffa046ce27>] radeon_fence_wait_seq_timeout.constprop.8+0x2e7/0x340 [radeon] [16081.310004] [<ffffffff81098be0>] ? __wake_up_sync+0x20/0x20 [16081.310013] [<ffffffffa046d186>] radeon_fence_wait+0x86/0xc0 [radeon] [16081.310023] [<ffffffffa047af6c>] radeon_flip_work_func+0x15c/0x190 [radeon] [16081.310025] [<ffffffff810709c4>] process_one_work+0x154/0x450 [16081.310026] [<ffffffff81070fbb>] worker_thread+0x6b/0x4d0 [16081.310028] [<ffffffff81070f50>] ? rescuer_thread+0x290/0x290 [16081.310029] [<ffffffff81075fed>] kthread+0xcd/0xf0 [16081.310031] [<ffffffff81075f20>] ? kthread_worker_fn+0x1d0/0x1d0 [16081.310034] [<ffffffff81725aec>] ret_from_fork+0x7c/0xb0 [16081.310035] [<ffffffff81075f20>] ? kthread_worker_fn+0x1d0/0x1d0
Rack #0/Slot #7 [AMD/ATI] Cayman XT [Radeon HD 6970]: INFO: task Xorg:10038 blocked for more than 120 seconds. Not tainted 3.18.9-rt4 #25 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Xorg D ffffffff816b7f88 0 10038 10032 0x10400004 ffff8800c5ad78e8 0000000000000002 ffff88041e80c460 000000000000c5c8 ffff88041e80c5c8 0000000000000002 000000000000c5a8 000000000000c5c8 ffff880417728000 ffff880414010000 000000000000000c ffff880414010000 Call Trace: [<ffffffff816b50f4>] schedule+0x34/0xa0 [<ffffffff816b72f4>] schedule_timeout+0x204/0x270 [<ffffffffa00cd8e6>] ? radeon_fence_process+0x16/0x40 [radeon] [<ffffffffa00cd954>] ? radeon_fence_any_seq_signaled+0x44/0x90 [radeon] [<ffffffffa00cdbc7>] radeon_fence_wait_seq_timeout.constprop.7+0x227/0x330 [radeon] [<ffffffff810ac310>] ? prepare_to_wait_event+0x110/0x110 [<ffffffffa00ce027>] radeon_fence_wait_any+0x57/0x70 [radeon] [<ffffffffa014334f>] radeon_sa_bo_new+0x2cf/0x4e0 [radeon] [<ffffffff8133c2a7>] ? debug_smp_processor_id+0x17/0x20 [<ffffffffa019d477>] radeon_ib_get+0x37/0xf0 [radeon] [<ffffffffa00e9a3d>] radeon_cs_ioctl+0x22d/0x820 [radeon] [<ffffffffa001bc04>] drm_ioctl+0x1a4/0x630 [drm] [<ffffffff8133c2a7>] ? debug_smp_processor_id+0x17/0x20 [<ffffffff8106e8da>] ? unpin_current_cpu+0x1a/0x70 [<ffffffff81097440>] ? migrate_enable+0xb0/0x1b0 [<ffffffffa00b004b>] radeon_drm_ioctl+0x4b/0x80 [radeon] [<ffffffff811c7040>] do_vfs_ioctl+0x2e0/0x4d0 [<ffffffff811d1aa2>] ? __fget+0x72/0xa0 [<ffffffff811c72b1>] SyS_ioctl+0x81/0xa0 [<ffffffff816b8cb2>] tracesys_phase2+0xd4/0xd9
Rack #4/Slot #1 Chipset: "KAVERI" (ChipID = 0x130c) [ 600.266245] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 600.281856] Xorg D 0000000000000002 0 3821 3812 0x00400080 [ 600.281865] ffff880223ddf908 0000000000000082 000000000000c1c0 000000000000c328 [ 600.281867] ffff88023720c328 0000000000000002 000000000000c308 000000000000c328 [ 600.281869] ffffffff81c1b480 ffff880036cfcb60 000000000000000c ffff880036cfcb60 [ 600.281873] Call Trace: [ 600.281882] [<ffffffff81736a14>] schedule+0x34/0xa0 [ 600.281885] [<ffffffff81738a44>] schedule_timeout+0x204/0x270 [ 600.281929] [<ffffffffa00b8756>] ? radeon_fence_process+0x16/0x40 [radeon] [ 600.281949] [<ffffffffa00b87c4>] ? radeon_fence_any_seq_signaled+0x44/0x90 [radeon] [ 600.281968] [<ffffffffa00b8a37>] radeon_fence_wait_seq_timeout.constprop.7+0x227/0x330 [radeon] [ 600.281972] [<ffffffff810815c0>] ? prepare_to_wait_event+0x110/0x110 [ 600.281992] [<ffffffffa00b8e97>] radeon_fence_wait_any+0x57/0x70 [radeon] [ 600.282023] [<ffffffffa012df5f>] radeon_sa_bo_new+0x2cf/0x4e0 [radeon] [ 600.282027] [<ffffffff81077a1e>] ? dequeue_task_fair+0x43e/0x650 [ 600.282055] [<ffffffffa0188087>] radeon_ib_get+0x37/0xf0 [radeon] [ 600.282078] [<ffffffffa00d46bd>] radeon_cs_ioctl+0x22d/0x820 [radeon] [ 600.282098] [<ffffffffa000ec04>] drm_ioctl+0x1a4/0x630 [drm] [ 600.282104] [<ffffffff810b2489>] ? do_futex+0x109/0xb20 [ 600.282106] [<ffffffff810787c6>] ? put_prev_entity+0x96/0x3f0 [ 600.282122] [<ffffffffa009b00e>] radeon_drm_ioctl+0xe/0x10 [radeon] [ 600.282125] [<ffffffff81190db0>] do_vfs_ioctl+0x2e0/0x4d0 [ 600.282128] [<ffffffff8119b792>] ? __fget+0x72/0xa0 [ 600.282131] [<ffffffff81191021>] SyS_ioctl+0x81/0xa0 [ 600.282134] [<ffffffff810d45c6>] ? __audit_syscall_exit+0x236/0x2e0 [ 600.282137] [<ffffffff8173a1d6>] system_call_fastpath+0x16/0x1b