CRIU swrk mode crash on restore (once)

[xemul]

https://api.travis-ci.org/jobs/176298120/log.txt?deansi=true

Core was generated by `../criu/criu swrk 4'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0x0000000000422ed9 in usernsd (sk=5) at criu/namespaces.c:1215
1215 BUG_ON(fd < 0 && flags & UNS_FDOUT);
(gdb) #0 0x0000000000422ed9 in usernsd (sk=5) at criu/namespaces.c:1215
#1 0x0000000000477c6c in start_usernsd () at criu/namespaces.c:1385
#2 0x000000000047a6b1 in prepare_namespace_before_tasks ()
at criu/namespaces.c:1684
#3 0x000000000042253d in restore_root_task (init=0x2b4b6c4c0458)
at criu/cr-restore.c:1796
#4 0x000000000044c514 in cr_restore_tasks () at criu/cr-restore.c:2069
#5 0x00000000004505cd in restore_using_req (sk=sk@entry=4,
req=) at criu/cr-service.c:562
#6 0x0000000000450984 in cr_service_work (sk=4) at criu/cr-service.c:931
#7 0x0000000000424323 in main (argc=3, argv=0x7fff312ddbe8,
envp=) at criu/crtools.c:319
(gdb) rax 0xdead04bf 3735880895
rbx 0x5 5
rcx 0x2b4b6c6d01fb 47602941624827
rdx 0x6 6
rsi 0xb3 179
rdi 0xb3 179
rbp 0x2 0x2
rsp 0x7fff312dd850 0x7fff312dd850
r8 0x0 0
r9 0x2b4b00000000 47601122541568
r10 0x7fff312dd610 140734018475536
r11 0x202 514
r12 0x752a 29994
r13 0x7fff312ddbe0 140734018477024
r14 0x0 0
r15 0x0 0
rip 0x422ed9 0x422ed9 <usernsd+364>
eflags 0x10203 [ CF IF RF ]
cs 0x33 51
ss 0x2b 43
ds 0x0 0
es 0x0 0
fs 0x0 0
gs 0x0 0
(gdb) Dump of assembler code from 0x422ec9 to 0x422ee9:
0x0000000000422ec9 <usernsd+348>: retq
0x0000000000422eca <usernsd+349>: cmpsb %es:(%rdi),%ds:(%rsi)
0x0000000000422ecb <usernsd+350>: (bad)
0x0000000000422ecc <usernsd+351>: decl -0x1(%rax)
0x0000000000422ecf <usernsd+354>: add $0x38814c,%eax
0x0000000000422ed4 <usernsd+359>: mov $0xdead04bf,%eax
=> 0x0000000000422ed9 <usernsd+364>: mov %rax,0x0
0x0000000000422ee1 <usernsd+372>: mov $0x7ab7e0,%edi
0x0000000000422ee6 <usernsd+377>: mov 0x14(%rsp),%edx
End of assembler dump.
(gdb) Dump of assembler code from 0x422ec9 to 0x422ee9:
0x0000000000422ec9 <usernsd+348>: retq
0x0000000000422eca <usernsd+349>: cmpsb %es:(%rdi),%ds:(%rsi)
0x0000000000422ecb <usernsd+350>: (bad)
0x0000000000422ecc <usernsd+351>: decl -0x1(%rax)
0x0000000000422ecf <usernsd+354>: add $0x38814c,%eax
0x0000000000422ed4 <usernsd+359>: mov $0xdead04bf,%eax
=> 0x0000000000422ed9 <usernsd+364>: mov %rax,0x0
0x0000000000422ee1 <usernsd+372>: mov $0x7ab7e0,%edi
0x0000000000422ee6 <usernsd+377>: mov 0x14(%rsp),%edx
End of assembler dump.
(gdb) quit

[xemul]

Cc @avagin and @efiop

[xemul]

64c2558
(then rolled back by d979f3f)

[github-actions]

A friendly reminder that this issue had no activity for 30 days.