FWIW, from the log I see that this was this program that triggered the bug:
2017/10/18 09:57:08 executing program 6:
mmap(&(0x7f0000000000/0xf64000)=nil, 0xf64000, 0x1, 0x31,
0xffffffffffffffff, 0x0)
mmap(&(0x7f0000000000/0xfff000)=nil, 0xfff000, 0x3, 0x32,
0xffffffffffffffff, 0x0)
r0 = accept4$ax25(0xffffffffffffff9c, 0x0, &(0x7f0000001000-0x4)=0x0, 0x800)
r1 = accept4$unix(0xffffffffffffffff, &(0x7f0000b8e000)=@file={0x0,
"0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000"},
&(0x7f0000ec1000)=0x55, 0x80000)
bind$unix(r1, &(0x7f00000fc000-0x8)=@abs={0x1, 0x0, 0x1}, 0x8)
mmap(&(0x7f0000000000/0x210000)=nil, 0x210000, 0x3, 0x32, r0, 0x0)
mmap(&(0x7f0000210000/0x1000)=nil, 0x1000, 0x3, 0x32, 0xffffffffffffffff, 0x0)
r2 = accept(r0, 0x0, &(0x7f0000211000-0x4)=0x0)
setsockopt$inet_sctp6_SCTP_INITMSG(r2, 0x84, 0x2,
&(0x7f00000f0000-0x8)={0x2, 0x80000001, 0x4000000abe5, 0x1}, 0x8)
setsockopt$netrom_NETROM_IDLE(r0, 0x103, 0x7,
&(0x7f00000d2000-0x4)=0x80000001, 0x4)
r3 = socket(0x10, 0x2, 0xc)
mmap(&(0x7f0000210000/0x1000)=nil, 0x1000, 0x3, 0x32, 0xffffffffffffffff, 0x0)
write(r3, &(0x7f00007b4000-0x20)="1f00000000011303f900d4e80788060c41ff200008000280061b0f0e000096fa",
0x20)
setsockopt$llc_int(r3, 0x10c, 0x8000000000006, &(0x7f0000f2d000-0x4)=0x2, 0x4)
r4 = socket$inet6(0xa, 0x1000000000000001, 0x800)
getsockopt$inet_sctp_SCTP_SOCKOPT_CONNECTX3(r3, 0x84, 0x6f,
&(0x7f0000b41000)={0x0, 0x3, &(0x7f0000f7d000-0x54)=[@in6={0xa, 0x0,
0x7fff, @empty={[0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0]}, 0x1000}, @in6={0xa, 0x3, 0x3,
@local={0xfe, 0x80, [0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0], 0x0, 0xaa}, 0x0}, @in6={0xa, 0x2, 0x5, @remote={0xfe, 0x80,
[0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0], 0x0,
0xbb}, 0x81}]}, &(0x7f00005fb000-0x4)=0x10)
getsockopt$inet_sctp6_SCTP_LOCAL_AUTH_CHUNKS(r3, 0x84, 0x1b,
&(0x7f00008d1000-0x1a)={<r5=>0x0, 0x12,
"8572e0f5c102f1d1755e06b25a03953c07d9"}, &(0x7f000017e000)=0x1a)
getsockopt$inet_sctp6_SCTP_PRIMARY_ADDR(r2, 0x84, 0x6,
&(0x7f0000699000-0x8c)={r5, @in6={{0xa, 0x2, 0x0, @empty={[0x0, 0x0,
0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0]}, 0xfffffffffffffffe}, [0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0, 0x0]}}, &(0x7f0000e4e000)=0x8c)
connect$inet6(r4, &(0x7f0000754000)={0xa, 0x0, 0xfffffffffffffffd,
@remote={0xfe, 0x80, [0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0,
0x0, 0x0, 0x0], 0x0, 0xbb}, 0x9}, 0x1c)
mmap(&(0x7f0000000000/0xfff000)=nil, 0xfff000, 0x3, 0x32,
0xffffffffffffffff, 0x0)
clock_gettime(0x0, &(0x7f000092c000-0x10)={0x0, 0x0})
futex(&(0x7f000000d000-0x4)=0x0, 0x0, 0x4,
&(0x7f000000b000)={0x77359400, 0x0}, &(0x7f0000cef000)=0x0, 0x0)
sendmmsg$unix(0xffffffffffffffff, &(0x7f000039b000)=[], 0x0, 0x0)
mkdir(&(0x7f0000f84000-0x8)="2e2f66696c653000", 0x0)
r6 = openat(0xffffffffffffff9c,
&(0x7f0000956000-0x8)="2e2f66696c653000", 0x408000, 0x40)
open(&(0x7f000038f000)="2e2f66696c653000", 0x400001, 0x20)
ioctl$PIO_FONTRESET(r6, 0x4b6d, 0x0)
unshare(0x20000)
mount(&(0x7f00004a4000-0x8)="2e2f66696c653000",
&(0x7f0000b7c000)="2e2f66696c653000",
&(0x7f00006d6000-0x6)="72616d667300", 0x0, &(0x7f0000691000-0x1)="")
r7 = inotify_init()
inotify_add_watch(r7, &(0x7f0000cc8000-0x8)="2e2f66696c653000", 0x14)
Bot wasn't able to reproduce the crash using this program, but it can
give hints as to what syscalls were executed.
There seems to be few things happened with the mount and
"2e2f66696c653000" path:
mkdir(&(0x7f0000f84000-0x8)="2e2f66696c653000", 0x0)
r6 = openat(0xffffffffffffff9c,
&(0x7f0000956000-0x8)="2e2f66696c653000", 0x408000, 0x40)
open(&(0x7f000038f000)="2e2f66696c653000", 0x400001, 0x20)
mount(&(0x7f00004a4000-0x8)="2e2f66696c653000",
&(0x7f0000b7c000)="2e2f66696c653000",
&(0x7f00006d6000-0x6)="72616d667300", 0x0, &(0x7f0000691000-0x1)="")
r7 = inotify_init()
inotify_add_watch(r7, &(0x7f0000cc8000-0x8)="2e2f66696c653000", 0x14)
But note that syscalls can be executed in parallel.