[Xenomai] ipipe: 4.4 BUG on x86, maybe on 4.9 as well

[Jan Kiszka]

Hi Philippe,

something got broken with the exception path rework:

[    2.619458] debug: unmapping init [mem 0xffffffff81b43000-0xffffffff81ee5fff]
[    2.622011] BUG: using __this_cpu_read() in preemptible [00000000] code: init/1
[    2.623446] caller is __this_cpu_preempt_check+0x13/0x20
[    2.624724] CPU: 2 PID: 1 Comm: init Not tainted 4.4.105+ #689
[    2.626073] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.11.0-0-g63451fca13-prebuilt.qemu-project.org 04/01/2014
[    2.628911] I-pipe domain: Linux
[    2.630083]  ffffffff81993439 ffff88003fb43c10 ffffffff813afa45 0000000000000002
[    2.631427]  ffff88003fb38000 ffff88003fb43c50 ffffffff813db5eb ffffffff82c57340
[    2.631427]  ffff88003fb43c98 0000000000000002 ffff88003fb44000 0000000000000000
[    2.631427] Call Trace:
[    2.631427]  [<ffffffff813afa45>] dump_stack+0xb2/0xdd
[    2.631427]  [<ffffffff813db5eb>] check_preemption_disabled+0x17b/0x1c0
[    2.631427]  [<ffffffff813db663>] __this_cpu_preempt_check+0x13/0x20
[    2.631427]  [<ffffffff8104eb1f>] do_page_fault+0x3f/0x60
[    2.631427]  [<ffffffff8170f8b7>] page_fault+0x27/0x60
[    2.631427]  [<ffffffff813bcef2>] ? __clear_user+0x42/0x70
[    2.631427]  [<ffffffff813bcf69>] clear_user+0x49/0x80
[    2.631427]  [<ffffffff812727d4>] padzero+0x24/0x40
[    2.631427]  [<ffffffff81274bfe>] load_elf_binary+0x8fe/0x10f0
[    2.631427]  [<ffffffff81116ee8>] ? ipipe_unstall_root+0x58/0x90
[    2.631427]  [<ffffffff812222c7>] search_binary_handler+0x97/0x1d0
[    2.631427]  [<ffffffff81223b86>] do_execveat_common.isra.40+0x5d6/0x7e0
[    2.631427]  [<ffffffff81223aff>] ? do_execveat_common.isra.40+0x54f/0x7e0
[    2.631427]  [<ffffffff8122bb00>] ? path_openat+0x1440/0x14e0
[    2.631427]  [<ffffffff816fff20>] ? rest_init+0xd0/0xd0
[    2.631427]  [<ffffffff81223dbc>] do_execve+0x2c/0x30
[    2.631427]  [<ffffffff810002eb>] run_init_process+0x2b/0x30
[    2.631427]  [<ffffffff816fff5d>] kernel_init+0x3d/0xe0
[    2.631427]  [<ffffffff8170d4c0>] ret_from_fork+0x40/0x70
[    2.631427]  [<ffffffff816fff20>] ? rest_init+0xd0/0xd0

Unless you have some immediate idea, I will debug this tomorrow. Issue
disappears when I revert the related patches in the ipipe queue.

I also have the build fix for 4.4 lined up, basically a backport of
"enable dev_printk() from the head stage" to that kernel. I've pushed
things to my for-upstream/4.4 branch, though they aren't ready yet.

Jan

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