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Subjectnet/ipv4: deadlock in ip_ra_control
Hello,

I've got the following deadlock report while running syzkaller fuzzer
on linux-next/51788aebe7cae79cb334ad50641347465fc188fd:

======================================================
[ INFO: possible circular locking dependency detected ]
4.10.0-next-20170301+ #1 Not tainted
-------------------------------------------------------
syz-executor1/3394 is trying to acquire lock:
(sk_lock-AF_INET){+.+.+.}, at: [<ffffffff838864cc>] lock_sock
include/net/sock.h:1460 [inline]
(sk_lock-AF_INET){+.+.+.}, at: [<ffffffff838864cc>]
do_ip_setsockopt.isra.12+0x21c/0x3540 net/ipv4/ip_sockglue.c:652

but task is already holding lock:
(rtnl_mutex){+.+.+.}, at: [<ffffffff836fbd97>] rtnl_lock+0x17/0x20
net/core/rtnetlink.c:70

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (rtnl_mutex){+.+.+.}:
validate_chain kernel/locking/lockdep.c:2265 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
__mutex_lock_common kernel/locking/mutex.c:754 [inline]
__mutex_lock+0x172/0x1730 kernel/locking/mutex.c:891
mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:906
rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
mrtsock_destruct+0x86/0x2c0 net/ipv4/ipmr.c:1281
ip_ra_control+0x459/0x600 net/ipv4/ip_sockglue.c:372
do_ip_setsockopt.isra.12+0x1064/0x3540 net/ipv4/ip_sockglue.c:1161
ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1264
raw_setsockopt+0xb7/0xd0 net/ipv4/raw.c:839
sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2725
SYSC_setsockopt net/socket.c:1786 [inline]
SyS_setsockopt+0x25c/0x390 net/socket.c:1765
entry_SYSCALL_64_fastpath+0x1f/0xc2

-> #0 (sk_lock-AF_INET){+.+.+.}:
check_prev_add kernel/locking/lockdep.c:1828 [inline]
check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1938
validate_chain kernel/locking/lockdep.c:2265 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
lock_sock_nested+0xcb/0x120 net/core/sock.c:2530
lock_sock include/net/sock.h:1460 [inline]
do_ip_setsockopt.isra.12+0x21c/0x3540 net/ipv4/ip_sockglue.c:652
ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1264
tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2721
sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2725
SYSC_setsockopt net/socket.c:1786 [inline]
SyS_setsockopt+0x25c/0x390 net/socket.c:1765
entry_SYSCALL_64_fastpath+0x1f/0xc2

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(rtnl_mutex);
lock(sk_lock-AF_INET);
lock(rtnl_mutex);
lock(sk_lock-AF_INET);

*** DEADLOCK ***

1 lock held by syz-executor1/3394:
#0: (rtnl_mutex){+.+.+.}, at: [<ffffffff836fbd97>]
rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70

stack backtrace:
CPU: 0 PID: 3394 Comm: syz-executor1 Not tainted 4.10.0-next-20170301+ #1
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:15 [inline]
dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
print_circular_bug+0x307/0x3b0 kernel/locking/lockdep.c:1202
check_prev_add kernel/locking/lockdep.c:1828 [inline]
check_prevs_add+0xa8f/0x19f0 kernel/locking/lockdep.c:1938
validate_chain kernel/locking/lockdep.c:2265 [inline]
__lock_acquire+0x2149/0x3430 kernel/locking/lockdep.c:3338
lock_acquire+0x2a1/0x630 kernel/locking/lockdep.c:3753
lock_sock_nested+0xcb/0x120 net/core/sock.c:2530
lock_sock include/net/sock.h:1460 [inline]
do_ip_setsockopt.isra.12+0x21c/0x3540 net/ipv4/ip_sockglue.c:652
ip_setsockopt+0x3a/0xb0 net/ipv4/ip_sockglue.c:1264
tcp_setsockopt+0x82/0xd0 net/ipv4/tcp.c:2721
sock_common_setsockopt+0x95/0xd0 net/core/sock.c:2725
SYSC_setsockopt net/socket.c:1786 [inline]
SyS_setsockopt+0x25c/0x390 net/socket.c:1765
entry_SYSCALL_64_fastpath+0x1f/0xc2

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