Re: [syzbot] [net?] possible deadlock in do_ipv6_setsockopt (4)

[syzbot <syzbot+3433b5cb8b2b70933f8d@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in smc_pnet_find_ism_resource

============================================
WARNING: possible recursive locking detected
6.13.0-syzkaller-09685-gc2933b2befe2-dirty #0 Not tainted
--------------------------------------------
syz.0.16/6653 is trying to acquire lock:
ffffffff8fcbf088 (rtnl_mutex){+.+.}-{4:4}, at: pnet_find_base_ndev net/smc/smc_pnet.c:945 [inline]
ffffffff8fcbf088 (rtnl_mutex){+.+.}-{4:4}, at: smc_pnet_find_ism_by_pnetid net/smc/smc_pnet.c:1101 [inline]
ffffffff8fcbf088 (rtnl_mutex){+.+.}-{4:4}, at: smc_pnet_find_ism_resource+0xe1/0x510 net/smc/smc_pnet.c:1152

but task is already holding lock:
ffffffff8fcbf088 (rtnl_mutex){+.+.}-{4:4}, at: smc_connect+0xb2/0xde0 net/smc/af_smc.c:1646

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

       CPU0
       ----
  lock(rtnl_mutex);
  lock(rtnl_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz.0.16/6653:
 #0: ffffffff8fcbf088 (rtnl_mutex){+.+.}-{4:4}, at: smc_connect+0xb2/0xde0 net/smc/af_smc.c:1646
 #1: ffff88806d868258 (sk_lock-AF_INET6){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1624 [inline]
 #1: ffff88806d868258 (sk_lock-AF_INET6){+.+.}-{0:0}, at: smc_connect+0xbc/0xde0 net/smc/af_smc.c:1647

stack backtrace:
CPU: 0 UID: 0 PID: 6653 Comm: syz.0.16 Not tainted 6.13.0-syzkaller-09685-gc2933b2befe2-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_deadlock_bug+0x483/0x620 kernel/locking/lockdep.c:3039
 check_deadlock kernel/locking/lockdep.c:3091 [inline]
 validate_chain+0x15e2/0x5920 kernel/locking/lockdep.c:3893
 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
 __mutex_lock_common kernel/locking/mutex.c:585 [inline]
 __mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730
 pnet_find_base_ndev net/smc/smc_pnet.c:945 [inline]
 smc_pnet_find_ism_by_pnetid net/smc/smc_pnet.c:1101 [inline]
 smc_pnet_find_ism_resource+0xe1/0x510 net/smc/smc_pnet.c:1152
 smc_find_ism_device net/smc/af_smc.c:1011 [inline]
 smc_find_proposal_devices net/smc/af_smc.c:1096 [inline]
 __smc_connect+0x391/0x1910 net/smc/af_smc.c:1526
 smc_connect+0x872/0xde0 net/smc/af_smc.c:1699
 __sys_connect_file net/socket.c:2040 [inline]
 __sys_connect+0x288/0x2d0 net/socket.c:2059
 __do_sys_connect net/socket.c:2065 [inline]
 __se_sys_connect net/socket.c:2062 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2062
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fbdb618cda9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fbdb7056038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007fbdb63a5fa0 RCX: 00007fbdb618cda9
RDX: 000000000000001c RSI: 0000000020000000 RDI: 0000000000000003
RBP: 00007fbdb620e2a0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007fbdb63a5fa0 R15: 00007fff45686908
 </TASK>


Tested on:

commit:         c2933b2b Merge tag 'net-6.14-rc1' of git://git.kernel...
git tree:       net-next
console output: https://syzkaller.appspot.com/x/log.txt?x=17c65724580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d033b14aeef39158
dashboard link: https://syzkaller.appspot.com/bug?extid=3433b5cb8b2b70933f8d
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13691764580000