Runtime trouble with commit dbd952127d (seccomp: introduce writer locking)

[Guenter Roeck <private@roeck-us.net>]

Hi folks,

I am having some trouble with commit dbd952127d (seccomp: introduce
writer locking) when running my qemu tests on the upstream kernel.

With powerpc, I get the following crash.

ftrace: allocating 20093 entries in 59 pages
------------[ cut here ]------------
kernel BUG at kernel/fork.c:1108!
Oops: Exception in kernel mode, sig: 5 [#1]
PREEMPT PowerMac
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 3.16.0-yocto-standard+ #1
task: c08a03d0 ti: c08e4000 task.ti: c08e4000
NIP: c002b98c LR: c002b988 CTR: c03837ec
REGS: c08e5e30 TRAP: 0700   Not tainted  (3.16.0-yocto-standard+)
MSR: 00021032 <ME,IR,DR,RI>  CR: 22282048  XER: 20000000

GPR00: c002b988 c08e5ee0 c08a03d0 00000001 c0a9b878 00000800 c783603c 00000020
GPR08: c783603c 00000003 00000001 c08f61fc 22222044 00000000 07c5ac10 00800300
GPR16: c7870000 00000010 00000000 07de7fa4 00000000 c08f594c c08f0000 c78702d0
GPR24: 00000000 c08f0000 c08f5940 c000422c c08a8ea0 c7870310 00000000 c7808400
NIP [c002b98c] copy_process.part.52+0x794/0x13e4
LR [c002b988] copy_process.part.52+0x790/0x13e4
Call Trace:
[c08e5ee0] [c002b988] copy_process.part.52+0x790/0x13e4 (unreliable)
[c08e5f60] [c002c768] do_fork+0xb8/0x3bc
[c08e5fa0] [c00041c8] rest_init+0x30/0x94
[c08e5fb0] [c083cf98] start_kernel+0x368/0x37c
[c08e5ff0] [00003438] 0x3438
Instruction dump:
7d400124 38600001 48027e95 55e903e1 41820b84 80e202c0 90f002c0 81420570
91500570 38600001 48027e75 39400001 <0f0a0000> 81420568 8162056c 91500568
---[ end trace dc8fa200cb88537f ]---

With  mips (both 32 bit and 64 bit), I get

NR_IRQS:256
CPU frequency 200.00 MHz
Console: colour dummy device 80x25
console [tty0] enabled
bootconsole [uart0] disabled

[ and then there is silence ]

In all cases I bisected the problem to the above mentioned commit.

Failures are seen in both linux-next and the tip of Linus' tree.
Test results are on http://server.roeck-us.net:8010/builders
(look for qwmu results). Build and test scripts are in the mips,
mips64, and powerpc subdirectories of
https://github.com/groeck/linux-build-test/tree/master/rootfs.

Any idea, anyone, what might be going on, or how I could do to
help tracking this down ?

Thanks,
Guenter