possible deadlock in inet_stream_connect

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 9ec5eea5 lib/parman: Delete newline
git tree: net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=11380d24d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=dbc1ca9e55dc1f9f
dashboard link: https://syzkaller.appspot.com/bug?extid=b0f5178b61ed7f3bbb46
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=177a6d14d00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10caeb02d00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b0f517...@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
5.11.0-rc7-syzkaller #0 Not tainted
--------------------------------------------
syz-executor845/10119 is trying to acquire lock:
ffff888021e6e320 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1598 [inline]
ffff888021e6e320 (sk_lock-AF_INET6){+.+.}-{0:0}, at: inet_stream_connect+0x3f/0xa0 net/ipv4/af_inet.c:724

but task is already holding lock:
ffff888022c1a520 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1598 [inline]
ffff888022c1a520 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp_stream_connect+0x85/0x800 net/mptcp/protocol.c:3171

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(sk_lock-AF_INET6);
lock(sk_lock-AF_INET6);

*** DEADLOCK ***

May be due to missing lock nesting notation

1 lock held by syz-executor845/10119:
#0: ffff888022c1a520 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1598 [inline]
#0: ffff888022c1a520 (sk_lock-AF_INET6){+.+.}-{0:0}, at: mptcp_stream_connect+0x85/0x800 net/mptcp/protocol.c:3171

stack backtrace:
CPU: 0 PID: 10119 Comm: syz-executor845 Not tainted 5.11.0-rc7-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x107/0x163 lib/dump_stack.c:120
print_deadlock_bug kernel/locking/lockdep.c:2761 [inline]
check_deadlock kernel/locking/lockdep.c:2804 [inline]
validate_chain kernel/locking/lockdep.c:3595 [inline]
__lock_acquire.cold+0x114/0x39e kernel/locking/lockdep.c:4832
lock_acquire kernel/locking/lockdep.c:5442 [inline]
lock_acquire+0x1a8/0x720 kernel/locking/lockdep.c:5407
lock_sock_nested+0xc5/0x110 net/core/sock.c:3071
lock_sock include/net/sock.h:1598 [inline]
inet_stream_connect+0x3f/0xa0 net/ipv4/af_inet.c:724
mptcp_stream_connect+0x156/0x800 net/mptcp/protocol.c:3200
__sys_connect_file+0x155/0x1a0 net/socket.c:1835
__sys_connect+0x161/0x190 net/socket.c:1852
__do_sys_connect net/socket.c:1862 [inline]
__se_sys_connect net/socket.c:1859 [inline]
__x64_sys_connect+0x6f/0xb0 net/socket.c:1859
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x443ce9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 a1 15 00 00 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 73 01 c3 48 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff5f9324e8 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000443ce9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 0000000000000000 R08: 000000a800000000 R09: 000000a800000000
R10: 000000a800000000 R11: 0000000000000246 R12: 00007fff5f932500
R13: 00007fff5f932510 R14: 0000000000014e11 R15: 00007fff5f9324f0


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[syzbot]

syzbot has bisected this issue to:

commit 40947e13997a1cba4e875893ca6e5d5e61a0689d
Author: Florian Westphal <f...@strlen.de>
Date: Fri Feb 12 23:59:56 2021 +0000

mptcp: schedule worker when subflow is closed

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=109b88f2d00000
start commit: 9ec5eea5 lib/parman: Delete newline
git tree: net-next
final oops: https://syzkaller.appspot.com/x/report.txt?x=129b88f2d00000
console output: https://syzkaller.appspot.com/x/log.txt?x=149b88f2d00000

kernel config: https://syzkaller.appspot.com/x/.config?x=dbc1ca9e55dc1f9f
dashboard link: https://syzkaller.appspot.com/bug?extid=b0f5178b61ed7f3bbb46
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=177a6d14d00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10caeb02d00000

Reported-by: syzbot+b0f517...@syzkaller.appspotmail.com
Fixes: 40947e13997a ("mptcp: schedule worker when subflow is closed")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.