"reuse mergeable anon_vma as parent when fork" causes a crash on s390

[Qian Cai]

The linux-next commit "mm/rmap.c: reuse mergeable anon_vma as parent when fork"
[1] causes a crash on s390 while compiling some C code. Reverted it fixes the
issue.

[1] https://lore.kernel.org/lkml/20191004160632.30251-1-richardw.yang@xxxxxxxxxxxxxxx/

00: [ÂÂ330.681233] vma 0000000049a08008 start 000003ff8ee7f000 end 000003ff8eee4
00: 000ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681233] next 000000004f272008 prev 0000000065c84230 mm 0000000037d1c1
00: 00ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681233] prot 711 anon_vma 000000001f4e4a80 vm_ops 0000000000000000ÂÂÂ
00: [ÂÂ330.681233] pgoff 3ff8ee7f file 0000000000000000 private_data 00000000000
00: 00000ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681233] flags: 0x8100073(read|write|mayread|maywrite|mayexec|account|
00: softdirty)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681344] ------------[ cut here ]------------ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681357] kernel BUG at include/linux/rmap.h:159!ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681442] illegal operation: 0001 ilc:1 [#1] SMP DEBUG_PAGEALLOCÂÂÂÂÂÂÂ
00: [ÂÂ330.681460] Modules linked in: ip_tables x_tables xfs dasd_fba_mod dasd_e
00: ckd_mod dm_mirror dm_region_hash dm_log dm_modÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681502] CPU: 0 PID: 7651 Comm: cc1 Not tainted 5.4.0-rc2-next-2019100
00: 9+ #4ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681516] Hardware name: IBM 2964 N96 400 (z/VM 6.4.0)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681530] Krnl PSW : 0704c00180000000 00000000531d9cac (__vma_adjust+0x
00: cf4/0xf30)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681561]ÂÂÂÂÂÂÂÂÂÂÂÂR:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0
00:ÂÂRI:0 EA:3ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681579] Krnl GPRS: 0000000000000001 0000030000000000 0000000000000146
00:ÂÂ000000006cc03da4ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681595]ÂÂÂÂÂÂÂÂÂÂÂÂ0000030000000000 000000005304378c 00000000513de008
00:ÂÂ0000000000000000ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681611]ÂÂÂÂÂÂÂÂÂÂÂÂ0000000049a08008 0000000049a08080 0000000000000000
00:ÂÂ000000005a178438ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681627]ÂÂÂÂÂÂÂÂÂÂÂÂ0000000053bae3b0 0000000037d1c100 00000000531d9ca8
00:ÂÂ00000000235ef880ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
01: HCPGSP2629I The virtual machine is placed in CP mode due to a SIGP stop from
ÂCPU 01.ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
01: HCPGSP2629I The virtual machine is placed in CP mode due to a SIGP stop from
ÂCPU 00.ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681668] Krnl Code: 00000000531d9c9c: fae0b9040028ÂÂÂÂÂÂÂÂapÂÂÂÂÂÂ2308
00: (15,%r11),40(1,%r0)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681668]ÂÂÂÂÂÂÂÂÂÂÂÂ00000000531d9ca2: c0e5ffff145fÂÂÂÂÂÂÂÂbraslÂÂÂ%r14
00: ,531bc560ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681668]ÂÂÂÂÂÂÂÂÂÂÂ#00000000531d9ca8: a7f40001ÂÂÂÂÂÂÂÂÂÂÂÂbrcÂÂÂÂÂ15,5
00: 31d9caaÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681668]ÂÂÂÂÂÂÂÂÂÂÂ>00000000531d9cac: c020005f1a5aÂÂÂÂÂÂÂÂlarlÂÂÂÂ%r2,
00: 53dbd160ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681668]ÂÂÂÂÂÂÂÂÂÂÂÂ00000000531d9cb2: c0e50015ec2bÂÂÂÂÂÂÂÂbraslÂÂÂ%r14
00: ,53497508ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681668]ÂÂÂÂÂÂÂÂÂÂÂÂ00000000531d9cb8: e320f0d80004ÂÂÂÂÂÂÂÂlgÂÂÂÂÂÂ%r2,
00: 216(%r15)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681668]ÂÂÂÂÂÂÂÂÂÂÂÂ00000000531d9cbe: c0e500040de1ÂÂÂÂÂÂÂÂbraslÂÂÂ%r14
00: ,5325b880ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.681668]ÂÂÂÂÂÂÂÂÂÂÂÂ00000000531d9cc4: 4120d038ÂÂÂÂÂÂÂÂÂÂÂÂlaÂÂÂÂÂÂ%r2,
00: 56(%r13)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682579] Call Trace:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682665] ([<00000000531d9ca8>] __vma_adjust+0xcf0/0xf30)ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682684]ÂÂ[<00000000531da4f0>] vma_merge+0x608/0x6b8ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682699]ÂÂ[<00000000531de3b8>] mmap_region+0x1e0/0x9b0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682713]ÂÂ[<00000000531defec>] do_mmap+0x464/0x650ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682730]ÂÂ[<00000000531930ba>] vm_mmap_pgoff+0x132/0x1c0ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682745]ÂÂ[<00000000531da7b4>] ksys_mmap_pgoff+0xd4/0x458ÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682761]ÂÂ[<00000000531dac54>] __s390x_sys_old_mmap+0xdc/0x108ÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682779]ÂÂ[<00000000537dcdd0>] system_call+0xd8/0x2b4ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682791] INFO: lockdep is turned off.ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682801] Last Breaking-Event-Address:ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682815]ÂÂ[<00000000531d9ca8>] __vma_adjust+0xcf0/0xf30ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ
00: [ÂÂ330.682833] Kernel panic - not syncing: Fatal exception: panic_on_oops