[syzbot] [smc?] possible deadlock in smc_diag_dump_proto

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8d245acc1e88 Merge tag 'char-misc-6.17-rc3' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=176fa7bc580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e1e1566c7726877e
dashboard link: https://syzkaller.appspot.com/bug?extid=50603c05bbdf4dfdaffa
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14e42062580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=12e42062580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/096739d8f0ec/disk-8d245acc.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/83a21aa9b978/vmlinux-8d245acc.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7e7f165a3b29/bzImage-8d245acc.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+50603c...@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/6109 is trying to acquire lock:
ffff8880b8823d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:44 [inline]
ffff8880b8823d90 ((softirq_ctrl.lock)){+.+.}-{3:3}, at: __local_bh_disable_ip+0x264/0x400 kernel/softirq.c:168

but task is already holding lock:
ffffffff8efa6608 (smc_v6_hashinfo.lock){++.+}-{3:3}, at: read_lock include/linux/rwlock_rt.h:37 [inline]
ffffffff8efa6608 (smc_v6_hashinfo.lock){++.+}-{3:3}, at: smc_diag_dump_proto+0x174/0x1fb0 net/smc/smc_diag.c:207

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (smc_v6_hashinfo.lock){++.+}-{3:3}:
lock_acquire+0x120/0x360 kernel/locking/lockdep.c:5868
rt_write_lock+0x6a/0x110 kernel/locking/spinlock_rt.c:242
write_lock_bh include/linux/rwlock_rt.h:99 [inline]
smc_hash_sk+0x8f/0x2a0 net/smc/af_smc.c:193
smc_sk_init+0x5a1/0x7f0 net/smc/af_smc.c:399
smc_sock_alloc net/smc/af_smc.c:420 [inline]
__smc_create+0x10d/0x280 net/smc/af_smc.c:3382
__sock_create+0x4b3/0x9f0 net/socket.c:1589
sock_create net/socket.c:1647 [inline]
__sys_socket_create net/socket.c:1684 [inline]
__sys_socket+0xd7/0x1b0 net/socket.c:1731
__do_sys_socket net/socket.c:1745 [inline]
__se_sys_socket net/socket.c:1743 [inline]
__x64_sys_socket+0x7a/0x90 net/socket.c:1743
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 ((softirq_ctrl.lock)){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385
__lock_release kernel/locking/lockdep.c:5574 [inline]
lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
__local_bh_enable_ip+0x10c/0x270 kernel/softirq.c:228
local_bh_enable include/linux/bottom_half.h:33 [inline]
sock_i_ino+0xa9/0xc0 net/core/sock.c:2800
smc_diag_msg_attrs_fill net/smc/smc_diag.c:68 [inline]
__smc_diag_dump net/smc/smc_diag.c:98 [inline]
smc_diag_dump_proto+0xa4c/0x1fb0 net/smc/smc_diag.c:217
smc_diag_dump+0x59/0xa0 net/smc/smc_diag.c:236
netlink_dump+0x6e4/0xe90 net/netlink/af_netlink.c:2327
__netlink_dump_start+0x5cb/0x7e0 net/netlink/af_netlink.c:2442
netlink_dump_start include/linux/netlink.h:341 [inline]
smc_diag_handler_dump+0x178/0x210 net/smc/smc_diag.c:251
sock_diag_rcv_msg+0x4c9/0x600 net/core/sock_diag.c:-1
netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x843/0xa10 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
sock_sendmsg_nosec net/socket.c:714 [inline]
__sock_sendmsg+0x219/0x270 net/socket.c:729
____sys_sendmsg+0x508/0x820 net/socket.c:2614
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
__sys_sendmsg net/socket.c:2700 [inline]
__do_sys_sendmsg net/socket.c:2705 [inline]
__se_sys_sendmsg net/socket.c:2703 [inline]
__x64_sys_sendmsg+0x1a1/0x260 net/socket.c:2703
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
rlock(smc_v6_hashinfo.lock);
lock((softirq_ctrl.lock));
lock(smc_v6_hashinfo.lock);
lock((softirq_ctrl.lock));

*** DEADLOCK ***

3 locks held by syz.0.17/6109:
#0: ffff888035fbe908 (nlk_cb_mutex-SOCK_DIAG){+.+.}-{4:4}, at: __netlink_dump_start+0xfe/0x7e0 net/netlink/af_netlink.c:2406
#1: ffffffff8efa6608 (smc_v6_hashinfo.lock){++.+}-{3:3}, at: read_lock include/linux/rwlock_rt.h:37 [inline]
#1: ffffffff8efa6608 (smc_v6_hashinfo.lock){++.+}-{3:3}, at: smc_diag_dump_proto+0x174/0x1fb0 net/smc/smc_diag.c:207
#2: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
#2: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
#2: ffffffff8d9a8b80 (rcu_read_lock){....}-{1:3}, at: rt_read_lock+0x1f8/0x360 kernel/locking/spinlock_rt.c:234

stack backtrace:
CPU: 0 UID: 0 PID: 6109 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_circular_bug+0x2ee/0x310 kernel/locking/lockdep.c:2043
check_noncircular+0x134/0x160 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3165 [inline]
check_prevs_add kernel/locking/lockdep.c:3284 [inline]
validate_chain+0xb9b/0x2140 kernel/locking/lockdep.c:3908
__lock_acquire+0xab9/0xd20 kernel/locking/lockdep.c:5237
reacquire_held_locks+0x127/0x1d0 kernel/locking/lockdep.c:5385
__lock_release kernel/locking/lockdep.c:5574 [inline]
lock_release+0x1b4/0x3e0 kernel/locking/lockdep.c:5889
__local_bh_enable_ip+0x10c/0x270 kernel/softirq.c:228
local_bh_enable include/linux/bottom_half.h:33 [inline]
sock_i_ino+0xa9/0xc0 net/core/sock.c:2800
smc_diag_msg_attrs_fill net/smc/smc_diag.c:68 [inline]
__smc_diag_dump net/smc/smc_diag.c:98 [inline]
smc_diag_dump_proto+0xa4c/0x1fb0 net/smc/smc_diag.c:217
smc_diag_dump+0x59/0xa0 net/smc/smc_diag.c:236
netlink_dump+0x6e4/0xe90 net/netlink/af_netlink.c:2327
__netlink_dump_start+0x5cb/0x7e0 net/netlink/af_netlink.c:2442
netlink_dump_start include/linux/netlink.h:341 [inline]
smc_diag_handler_dump+0x178/0x210 net/smc/smc_diag.c:251
sock_diag_rcv_msg+0x4c9/0x600 net/core/sock_diag.c:-1
netlink_rcv_skb+0x205/0x470 net/netlink/af_netlink.c:2552
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x843/0xa10 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
sock_sendmsg_nosec net/socket.c:714 [inline]
__sock_sendmsg+0x219/0x270 net/socket.c:729
____sys_sendmsg+0x508/0x820 net/socket.c:2614
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
__sys_sendmsg net/socket.c:2700 [inline]
__do_sys_sendmsg net/socket.c:2705 [inline]
__se_sys_sendmsg net/socket.c:2703 [inline]
__x64_sys_sendmsg+0x1a1/0x260 net/socket.c:2703
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe07d70ebe9
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:00007ffe932c2428 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fe07d935fa0 RCX: 00007fe07d70ebe9
RDX: 0000000000004000 RSI: 0000200000000140 RDI: 0000000000000004
RBP: 00007fe07d791e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe07d935fa0 R14: 00007fe07d935fa0 R15: 0000000000000003
</TASK>


---
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