Re: [syzbot] [lvs?] possible deadlock in start_sync_thread

[syzbot <syzbot+e929093395ec65f969c7@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    6c52d4da1c74 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=12889630580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=672325e7ab17fdf7
dashboard link: https://syzkaller.appspot.com/bug?extid=e929093395ec65f969c7
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1788e187980000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14a4f2a7980000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/70526f6a5c28/disk-6c52d4da.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/8ca3cd20d331/vmlinux-6c52d4da.xz
kernel image: https://storage.googleapis.com/syzbot-assets/9c4393fc9a08/bzImage-6c52d4da.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e929093395ec65f969c7@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.12.0-rc5-syzkaller-00181-g6c52d4da1c74 #0 Not tainted
------------------------------------------------------
syz-executor158/5839 is trying to acquire lock:
ffffffff8fcd3448 (rtnl_mutex){+.+.}-{3:3}, at: start_sync_thread+0xdc/0x2dc0 net/netfilter/ipvs/ip_vs_sync.c:1761

but task is already holding lock:
ffff888034ac8aa8 (&smc->clcsock_release_lock){+.+.}-{3:3}, at: smc_setsockopt+0x1c3/0xe50 net/smc/af_smc.c:3056

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&smc->clcsock_release_lock){+.+.}-{3:3}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:608 [inline]
       __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
       smc_switch_to_fallback+0x35/0xdb0 net/smc/af_smc.c:902
       smc_sendmsg+0x11f/0x530 net/smc/af_smc.c:2771
       sock_sendmsg_nosec net/socket.c:729 [inline]
       __sock_sendmsg+0x221/0x270 net/socket.c:744
       __sys_sendto+0x39b/0x4f0 net/socket.c:2214
       __do_sys_sendto net/socket.c:2226 [inline]
       __se_sys_sendto net/socket.c:2222 [inline]
       __x64_sys_sendto+0xde/0x100 net/socket.c:2222
       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

-> #1 (sk_lock-AF_INET){+.+.}-{0:0}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5825
       lock_sock_nested+0x48/0x100 net/core/sock.c:3611
       do_ip_setsockopt+0x1a2d/0x3cd0 net/ipv4/ip_sockglue.c:1078
       ip_setsockopt+0x63/0x100 net/ipv4/ip_sockglue.c:1417
       do_sock_setsockopt+0x3af/0x720 net/socket.c:2334
       __sys_setsockopt+0x1a2/0x250 net/socket.c:2357
       __do_sys_setsockopt net/socket.c:2366 [inline]
       __se_sys_setsockopt net/socket.c:2363 [inline]
       __x64_sys_setsockopt+0xb5/0xd0 net/socket.c:2363
       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

-> #0 (rtnl_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3161 [inline]
       check_prevs_add kernel/locking/lockdep.c:3280 [inline]
       validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904
       __lock_acquire+0x1384/0x2050 kernel/locking/lockdep.c:5202
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5825
       __mutex_lock_common kernel/locking/mutex.c:608 [inline]
       __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
       start_sync_thread+0xdc/0x2dc0 net/netfilter/ipvs/ip_vs_sync.c:1761
       do_ip_vs_set_ctl+0x442/0x13d0 net/netfilter/ipvs/ip_vs_ctl.c:2732
       nf_setsockopt+0x295/0x2c0 net/netfilter/nf_sockopt.c:101
       smc_setsockopt+0x275/0xe50 net/smc/af_smc.c:3064
       do_sock_setsockopt+0x3af/0x720 net/socket.c:2334
       __sys_setsockopt+0x1a2/0x250 net/socket.c:2357
       __do_sys_setsockopt net/socket.c:2366 [inline]
       __se_sys_setsockopt net/socket.c:2363 [inline]
       __x64_sys_setsockopt+0xb5/0xd0 net/socket.c:2363
       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

other info that might help us debug this:

Chain exists of:
  rtnl_mutex --> sk_lock-AF_INET --> &smc->clcsock_release_lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&smc->clcsock_release_lock);
                               lock(sk_lock-AF_INET);
                               lock(&smc->clcsock_release_lock);
  lock(rtnl_mutex);

 *** DEADLOCK ***

1 lock held by syz-executor158/5839:
 #0: ffff888034ac8aa8 (&smc->clcsock_release_lock){+.+.}-{3:3}, at: smc_setsockopt+0x1c3/0xe50 net/smc/af_smc.c:3056

stack backtrace:
CPU: 0 UID: 0 PID: 5839 Comm: syz-executor158 Not tainted 6.12.0-rc5-syzkaller-00181-g6c52d4da1c74 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2074
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2206
 check_prev_add kernel/locking/lockdep.c:3161 [inline]
 check_prevs_add kernel/locking/lockdep.c:3280 [inline]
 validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904
 __lock_acquire+0x1384/0x2050 kernel/locking/lockdep.c:5202
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:608 [inline]
 __mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
 start_sync_thread+0xdc/0x2dc0 net/netfilter/ipvs/ip_vs_sync.c:1761
 do_ip_vs_set_ctl+0x442/0x13d0 net/netfilter/ipvs/ip_vs_ctl.c:2732
 nf_setsockopt+0x295/0x2c0 net/netfilter/nf_sockopt.c:101
 smc_setsockopt+0x275/0xe50 net/smc/af_smc.c:3064
 do_sock_setsockopt+0x3af/0x720 net/socket.c:2334
 __sys_setsockopt+0x1a2/0x250 net/socket.c:2357
 __do_sys_setsockopt net/socket.c:2366 [inline]
 __se_sys_setsockopt net/socket.c:2363 [inline]
 __x64_sys_setsockopt+0xb5/0xd0 net/socket.c:2363
 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: 0033:0x7f468bc1c369
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe79331b18 EFLAGS: 00000246 ORIG_RAX: 0000000000000036
RAX: ffffffffffffffda RBX: 00007ffe79331ce8 RCX: 00007f468bc1c369
RDX: 000000000000048b RSI: 0000000000000000 RDI: 0000000000000005
RBP: 00007f468bc8f610 R08: 0000000000000018 R09: 00007ffe79331ce8
R10: 0000000020000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffe79331cd8 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
IPVS: Unkn


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