WARNING: suspicious RCU usage in pid_task

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    f0dc7f9c6dd9 Merge git://git.kernel.org/pub/scm/linux/kern..
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=124b698f800000
kernel config:  https://syzkaller.appspot.com/x/.config?x=fa9c20c48788d1c1
dashboard link: https://syzkaller.appspot.com/bug?extid=c2d4c3ae3fd90bbaf059
compiler:       gcc (GCC) 8.0.1 20180413 (experimental)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+c2d4c3ae3fd90bbaf059@xxxxxxxxxxxxxxxxxxxxxxxxx

bpfilter: read fail -512

=============================
WARNING: suspicious RCU usage
4.17.0+ #84 Not tainted
-----------------------------
kernel/pid.c:323 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by syz-executor7/29997:
device lo entered promiscuous mode
 #0: 000000001e4dec85 (bpfilter_lock){+.+.}, at:  
__bpfilter_process_sockopt+0x1bd/0x384 net/bpfilter/bpfilter_kern.c:67

stack backtrace:
CPU: 1 PID: 29997 Comm: syz-executor7 Not tainted 4.17.0+ #84
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS  
Google 01/01/2011
IPVS: ftp: loaded support on port[0] = 21
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1b9/0x294 lib/dump_stack.c:113
 lockdep_rcu_suspicious+0x14a/0x153 kernel/locking/lockdep.c:4562
 pid_task+0x1b9/0x1e0 kernel/pid.c:322
 shutdown_umh.constprop.0+0x33/0x7c net/bpfilter/bpfilter_kern.c:29
 __stop_umh net/bpfilter/bpfilter_kern.c:41 [inline]
 __bpfilter_process_sockopt.cold.1+0x9b/0xa0 net/bpfilter/bpfilter_kern.c:81
 bpfilter_mbox_request+0x4d/0xb0 net/ipv4/bpfilter/sockopt.c:25
 bpfilter_ip_get_sockopt+0x6b/0x90 net/ipv4/bpfilter/sockopt.c:42
 ip_getsockopt+0x238/0x2a0 net/ipv4/ip_sockglue.c:1563
 tcp_getsockopt+0x93/0xe0 net/ipv4/tcp.c:3534
 sock_common_getsockopt+0x9a/0xe0 net/core/sock.c:3012
 smc_getsockopt+0xc7/0x120 net/smc/af_smc.c:1473
 __sys_getsockopt+0x1a5/0x370 net/socket.c:1984
 __do_sys_getsockopt net/socket.c:1995 [inline]
 __se_sys_getsockopt net/socket.c:1992 [inline]
 __x64_sys_getsockopt+0xbe/0x150 net/socket.c:1992
 do_syscall_64+0x1b1/0x800 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x455b29
Code: 1d ba fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7  
48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff  
ff 0f 83 eb b9 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f0391bdbc68 EFLAGS: 00000246 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 00007f0391bdc6d4 RCX: 0000000000455b29
RDX: 0000000000000043 RSI: 0000000000000000 RDI: 0000000000000016
RBP: 000000000072bea0 R08: 0000000020000040 R09: 0000000000000000
R10: 0000000020000000 R11: 0000000000000246 R12: 00000000ffffffff
R13: 00000000004c3808 R14: 00000000004c8f78 R15: 0000000000000000
netlink: 220 bytes leftover after parsing attributes in process  
`syz-executor2'.


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