======================================================
WARNING: possible circular locking dependency detected
4.16.0+ #11 Not tainted
------------------------------------------------------
syzkaller336064/4489 is trying to acquire lock:
000000005f8bfa0f (&mm->mmap_sem){++++}, at: __might_fault+0xfb/0x1e0 mm/memory.c:4554

but task is already holding lock:
0000000098e7a1e2 (sk_lock-AF_INET6){+.+.}, at: lock_sock include/net/sock.h:1469 [inline]
0000000098e7a1e2 (sk_lock-AF_INET6){+.+.}, at: do_ipv6_setsockopt.isra.9+0x5ba/0x4660 net/ipv6/ipv6_sockglue.c:167

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (sk_lock-AF_INET6){+.+.}:
       lock_sock_nested+0xd0/0x120 net/core/sock.c:2844
       lock_sock include/net/sock.h:1469 [inline]
       tcp_mmap+0x1c7/0x14f0 net/ipv4/tcp.c:1759
       sock_mmap+0x8e/0xc0 net/socket.c:1144
       call_mmap include/linux/fs.h:1789 [inline]
       mmap_region+0xd13/0x1820 mm/mmap.c:1723
       do_mmap+0xc79/0x11d0 mm/mmap.c:1494
       do_mmap_pgoff include/linux/mm.h:2237 [inline]
       vm_mmap_pgoff+0x1fb/0x2a0 mm/util.c:355
       ksys_mmap_pgoff+0x4c9/0x640 mm/mmap.c:1544
       SYSC_mmap arch/x86/kernel/sys_x86_64.c:100 [inline]
       SyS_mmap+0x16/0x20 arch/x86/kernel/sys_x86_64.c:91
       do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
       entry_SYSCALL_64_after_hwframe+0x42/0xb7

-> #0 (&mm->mmap_sem){++++}:
       lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
       __might_fault+0x155/0x1e0 mm/memory.c:4555
       _copy_from_user+0x30/0x150 lib/usercopy.c:10
       copy_from_user include/linux/uaccess.h:147 [inline]
       do_ipv6_setsockopt.isra.9+0x2a78/0x4660 net/ipv6/ipv6_sockglue.c:474
       ipv6_setsockopt+0xbd/0x170 net/ipv6/ipv6_sockglue.c:922
       sctp_setsockopt+0x2da/0x7000 net/sctp/socket.c:4212
       sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:3042
       __sys_setsockopt+0x1bd/0x390 net/socket.c:1903
       SYSC_setsockopt net/socket.c:1914 [inline]
       SyS_setsockopt+0x34/0x50 net/socket.c:1911
       do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
       entry_SYSCALL_64_after_hwframe+0x42/0xb7

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(sk_lock-AF_INET6);
                               lock(&mm->mmap_sem);
                               lock(sk_lock-AF_INET6);
  lock(&mm->mmap_sem);

 *** DEADLOCK ***

1 lock held by syzkaller336064/4489:
 #0: 0000000098e7a1e2 (sk_lock-AF_INET6){+.+.}, at: lock_sock include/net/sock.h:1469 [inline]
 #0: 0000000098e7a1e2 (sk_lock-AF_INET6){+.+.}, at: do_ipv6_setsockopt.isra.9+0x5ba/0x4660 net/ipv6/ipv6_sockglue.c:167

stack backtrace:
CPU: 0 PID: 4489 Comm: syzkaller336064 Not tainted 4.16.0+ #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 print_circular_bug.isra.36.cold.54+0x1bd/0x27d kernel/locking/lockdep.c:1223
 check_prev_add kernel/locking/lockdep.c:1863 [inline]
 check_prevs_add kernel/locking/lockdep.c:1976 [inline]
 validate_chain kernel/locking/lockdep.c:2417 [inline]
 __lock_acquire+0x343e/0x5140 kernel/locking/lockdep.c:3431
 lock_acquire+0x1dc/0x520 kernel/locking/lockdep.c:3920
 __might_fault+0x155/0x1e0 mm/memory.c:4555
 _copy_from_user+0x30/0x150 lib/usercopy.c:10
 copy_from_user include/linux/uaccess.h:147 [inline]
 do_ipv6_setsockopt.isra.9+0x2a78/0x4660 net/ipv6/ipv6_sockglue.c:474
 ipv6_setsockopt+0xbd/0x170 net/ipv6/ipv6_sockglue.c:922
 sctp_setsockopt+0x2da/0x7000 net/sctp/socket.c:4212
 sock_common_setsockopt+0x9a/0xe0 net/core/sock.c:3042
 __sys_setsockopt+0x1bd/0x390 net/socket.c:1903
 SYSC_setsockopt net/socket.c:1914 [inline]
 SyS_setsockopt+0x34/0x50 net/socket.c:1911
 do_syscall_64+0x29e/0x9d0 arch/x86/entry/common.c:287
 entry_SYSCALL_64_after_hwframe+0x42/0xb7
RIP: 0033:0x43fe59
RSP: 002b:00007fff7135f748 EFLAGS: 00000217 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fe59
RDX: 0000000000000032 RSI: 0000000000000029 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000108 R09: 00000000004002c8
R10: 0000000020000140 R11: 0000000000000217 R12: 0000000000401780