On Sat, 2018-08-18 at 12:29 +0200, Mike Galbraith wrote:

On Fri, 2018-08-17 at 16:23 -0400, Steven Rostedt wrote:

quoted

Pulling in stable releases into v4.14-rt I triggered this with my CPU
hotplug test:

------------[ cut here ]------------
kernel BUG at /work/rt/stable-rt.git/kernel/sched/core.c:1639!
invalid opcode: 0000 [#1] PREEMPT SMP PTI
Modules linked in: sunrpc ip6t_REJECT nf_reject_ipv6 nf_conntrack_ipv6 nf_defrag_ipv6 ip6table_filter ip6_tables uinput snd_hda_codec_idt snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_seq snd_seq_device snd_pcm snd_timer snd shpchp i2c_i801 soundcore floppy i915 drm_kms_helper drm fb_sys_fops sysimgblt sysfillrect syscopyarea i2c_algo_bit iosf_mbi video [last unloaded: speedstep_lib]
CPU: 1 PID: 2944 Comm: mkdumprd Not tainted 4.14.63-test-rt40+ #782
Hardware name: To Be Filled By O.E.M. To Be Filled By O.E.M./To be filled by O.E.M., BIOS SDBLI944.86P 05/08/2007
task: ffff880037888d80 task.stack: ffffc90000538000
RIP: 0010:select_fallback_rq+0xc3/0x122

I noticed this upstream, and had started hunting for the origin, but
had thought that 4.14-rt was OK.  Clearly not the case, but it's not
4.14.60.. stable changes interacting badly either, virgin 4.14.59-rt37
just reproduced in a vm clone of my workstation.

4.15.18-rt37 (4.14-rt rolled forward) does not reproduce, nor does
4.16.18-rt12, but 4.17.0-rt5 (v4.16.12-rt5 rolled forward) does, so
seems it has be something from the 4.17 cycle that went back to 4.14-
stable after 4.1[56]-stable trees went extinct.

	-Mike