shm broken on MIPS in current -git

[Manuel Lauss]

Hello Vasiliy,

Commits 5774ed014f02120db9a6945a1ecebeb97c2acccb
(shm: handle separate PID namespaces case)
and 4c677e2eefdba9c5bfc4474e2e91b26ae8458a1d
(shm: optimize locking and ipc_namespace getting)
break on my MIPS systems.  The following oops is
printed on boot, and as a result, more than  300 zombie kworker
kernel processes are resident.  I don't see this oops on x86 or x64.

ra points to the down_write() in ipc/shm.c::exit_shm()

CPU 0 Unable to handle kernel paging request at virtual address
00000000, epc == 80527c64, ra == 8024afb8
Oops[#1]:
Cpu 0
$ 0   : 00000000 10003c00 00000000 10003c01
$ 4   : 8060d114 8fc45e60 8060d118 8fc3f520
$ 8   : 00000000 01312d00 0016e35f 00020000
$12   : 00000080 00000010 00000010 8fc3001c
$16   : 8fc3f520 00000000 00000000 00000000
$20   : 00000000 00000000 8fc45eb4 00000000
$24   : 00000000 8011f9b0
$28   : 8fc44000 8fc45e50 00000001 8024afb8
Hi    : 00000000
Lo    : 01312d00
epc   : 80527c64 __down_write_nested+0x68/0xf0
    Not tainted
ra    : 8024afb8 exit_shm+0x30/0x64
Status: 10003c02    KERNEL EXL
Cause : 0080800c
BadVA : 00000000
PrId  : 800c8000 (Au1300)
Process kworker/u:0 (pid: 9, threadinfo=8fc44000, task=8fc3f520, tls=00000000)
Stack : 14200972 d3054429 00000000 56b8e493 8060d118 00000000 8fc3f520 00000002
        8fc2c000 8060d114 00000000 8024afb8 00000000 00000000 00000000 00000000
        8060d0c0 00000000 8fc3f520 80128ae8 30480023 0b309f84 34ffeedb ef9e65d6
        38019941 af430015 f6d9ebeb 00000000 00000000 00000000 8fc29ce0 8fc15300
        00000000 00000000 00000000 00000000 00000000 00000000 00000000 80139578
        ...
Call Trace:
[<80527c64>] __down_write_nested+0x68/0xf0
[<8024afb8>] exit_shm+0x30/0x64
[<80128ae8>] do_exit+0x50c/0x664
[<80139578>] ____call_usermodehelper+0xfc/0x118
[<801061bc>] kernel_thread_helper+0x10/0x18


Code: ac850008  afa60010  afa20014 <ac450000> 40016000  30630001
3421001f  3821001f  00611825
Disabling lock debugging due to kernel taint
Fixing recursive fault but reboot is needed!


Thanks,
        Manuel Lauss
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