syzbot

======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Not tainted
------------------------------------------------------
syz.0.17/6130 is trying to acquire lock:
ffff88803976da20 (slock-AF_PHONET/1){+.+.}-{3:3}, at: __sk_receive_skb+0x1bf/0x9e0 net/core/sock.c:563

but task is already holding lock:
ffff88803976e2e0 (slock-AF_PHONET){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
ffff88803976e2e0 (slock-AF_PHONET){+...}-{3:3}, at: __sk_receive_skb+0x1f1/0x9e0 net/core/sock.c:565

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (slock-AF_PHONET){+...}-{3:3}:
       rt_spin_lock+0x83/0x400 kernel/locking/spinlock_rt.c:56
       spin_lock include/linux/spinlock_rt.h:45 [inline]
       __sk_receive_skb+0x1f1/0x9e0 net/core/sock.c:565
       sk_receive_skb include/net/sock.h:2022 [inline]
       phonet_rcv+0x781/0xc40 net/phonet/af_phonet.c:-1
       __netif_receive_skb_one_core net/core/dev.c:6210 [inline]
       __netif_receive_skb net/core/dev.c:6323 [inline]
       process_backlog+0x5e1/0xc60 net/core/dev.c:6674
       __napi_poll+0xab/0x550 net/core/dev.c:7738
       napi_poll net/core/dev.c:7801 [inline]
       net_rx_action+0x696/0xe00 net/core/dev.c:7958
       handle_softirqs+0x1de/0x6d0 kernel/softirq.c:626
       __do_softirq kernel/softirq.c:660 [inline]
       __local_bh_enable_ip+0x170/0x2b0 kernel/softirq.c:302
       local_bh_enable include/linux/bottom_half.h:33 [inline]
       netif_rx+0xb9/0xf0 net/core/dev.c:5776
       pn_send+0x62a/0x8e0 net/phonet/af_phonet.c:188
       pn_skb_send+0x218/0x530 net/phonet/af_phonet.c:275
       pep_indicate net/phonet/pep.c:123 [inline]
       pipe_snd_status+0x1f1/0x320 net/phonet/pep.c:221
       pipe_grant_credits net/phonet/pep.c:244 [inline]
       pipe_do_rcv+0xf15/0x16a0 net/phonet/pep.c:433
       sk_backlog_rcv include/net/sock.h:1190 [inline]
       __sk_receive_skb+0x962/0x9e0 net/core/sock.c:572
       sk_receive_skb include/net/sock.h:2022 [inline]
       pep_do_rcv+0x685/0xaa0 net/phonet/pep.c:675
       sk_backlog_rcv include/net/sock.h:1190 [inline]
       __release_sock+0x2a9/0x3d0 net/core/sock.c:3216
       release_sock+0x1be/0x290 net/core/sock.c:3815
       pep_sock_accept+0xd47/0x11e0 net/phonet/pep.c:879
       pn_socket_accept+0xc1/0x310 net/phonet/socket.c:303
       do_accept+0x6ca/0x930 net/socket.c:2062
       __sys_accept4_file net/socket.c:2096 [inline]
       __sys_accept4+0x139/0x230 net/socket.c:2118
       __do_sys_accept4 net/socket.c:2125 [inline]
       __se_sys_accept4 net/socket.c:2122 [inline]
       __x64_sys_accept4+0x9a/0xb0 net/socket.c:2122
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (slock-AF_PHONET/1){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:3167 [inline]
       check_prevs_add kernel/locking/lockdep.c:3286 [inline]
       validate_chain kernel/locking/lockdep.c:3910 [inline]
       __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5239
       lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870
       rt_spin_lock_nested+0x81/0x3f0 kernel/locking/spinlock_rt.c:64
       __sk_receive_skb+0x1bf/0x9e0 net/core/sock.c:563
       sk_receive_skb include/net/sock.h:2022 [inline]
       pep_do_rcv+0x685/0xaa0 net/phonet/pep.c:675
       sk_backlog_rcv include/net/sock.h:1190 [inline]
       __sk_receive_skb+0x962/0x9e0 net/core/sock.c:572
       sk_receive_skb include/net/sock.h:2022 [inline]
       phonet_rcv+0x781/0xc40 net/phonet/af_phonet.c:-1
       __netif_receive_skb_one_core net/core/dev.c:6210 [inline]
       __netif_receive_skb net/core/dev.c:6323 [inline]
       process_backlog+0x5e1/0xc60 net/core/dev.c:6674
       __napi_poll+0xab/0x550 net/core/dev.c:7738
       napi_poll net/core/dev.c:7801 [inline]
       net_rx_action+0x696/0xe00 net/core/dev.c:7958
       handle_softirqs+0x1de/0x6d0 kernel/softirq.c:626
       __do_softirq kernel/softirq.c:660 [inline]
       __local_bh_enable_ip+0x170/0x2b0 kernel/softirq.c:302
       local_bh_enable include/linux/bottom_half.h:33 [inline]
       netif_rx+0xb9/0xf0 net/core/dev.c:5776
       pn_send+0x62a/0x8e0 net/phonet/af_phonet.c:188
       pn_skb_send+0x218/0x530 net/phonet/af_phonet.c:275
       pipe_skb_send+0x2f7/0x540 net/phonet/pep.c:1130
       pep_sendmsg+0x9ca/0xb00 net/phonet/pep.c:1206
       pn_socket_sendmsg+0x1e5/0x250 net/phonet/socket.c:424
       sock_sendmsg_nosec+0x112/0x150 net/socket.c:797
       __sock_sendmsg net/socket.c:812 [inline]
       sock_write_iter+0x308/0x410 net/socket.c:1269
       new_sync_write fs/read_write.c:595 [inline]
       vfs_write+0x629/0xba0 fs/read_write.c:688
       ksys_write+0x156/0x270 fs/read_write.c:740
       do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
       do_syscall_64+0x15f/0xf80 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
       ----                    ----
  lock(slock-AF_PHONET);
                               lock(slock-AF_PHONET/1);
                               lock(slock-AF_PHONET);
  lock(slock-AF_PHONET/1);

 *** DEADLOCK ***

6 locks held by syz.0.17/6130:
 #0: ffff88803aded218 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline]
 #0: ffff88803aded218 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: pep_sendmsg+0x7b6/0xb00 net/phonet/pep.c:1199
 #1: ffffffff8e3c8140 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163
 #2: ffffffff8e3c8140 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #2: ffffffff8e3c8140 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #2: ffffffff8e3c8140 (rcu_read_lock){....}-{1:3}, at: process_backlog+0x271/0xc60 net/core/dev.c:6673
 #3: ffff88803976e2e0 (slock-AF_PHONET){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline]
 #3: ffff88803976e2e0 (slock-AF_PHONET){+...}-{3:3}, at: __sk_receive_skb+0x1f1/0x9e0 net/core/sock.c:565
 #4: ffffffff8e3c8140 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #4: ffffffff8e3c8140 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #4: ffffffff8e3c8140 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline]
 #4: ffffffff8e3c8140 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1e0/0x400 kernel/locking/spinlock_rt.c:57
 #5: ffff88803976e398 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: sk_receive_skb include/net/sock.h:2022 [inline]
 #5: ffff88803976e398 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: phonet_rcv+0x781/0xc40 net/phonet/af_phonet.c:-1

stack backtrace:
CPU: 0 UID: 0 PID: 6130 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2045
 check_noncircular+0x12e/0x150 kernel/locking/lockdep.c:2177
 check_prev_add kernel/locking/lockdep.c:3167 [inline]
 check_prevs_add kernel/locking/lockdep.c:3286 [inline]
 validate_chain kernel/locking/lockdep.c:3910 [inline]
 __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5239
 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5870
 rt_spin_lock_nested+0x81/0x3f0 kernel/locking/spinlock_rt.c:64
 __sk_receive_skb+0x1bf/0x9e0 net/core/sock.c:563
 sk_receive_skb include/net/sock.h:2022 [inline]
 pep_do_rcv+0x685/0xaa0 net/phonet/pep.c:675
 sk_backlog_rcv include/net/sock.h:1190 [inline]
 __sk_receive_skb+0x962/0x9e0 net/core/sock.c:572
 sk_receive_skb include/net/sock.h:2022 [inline]
 phonet_rcv+0x781/0xc40 net/phonet/af_phonet.c:-1
 __netif_receive_skb_one_core net/core/dev.c:6210 [inline]
 __netif_receive_skb net/core/dev.c:6323 [inline]
 process_backlog+0x5e1/0xc60 net/core/dev.c:6674
 __napi_poll+0xab/0x550 net/core/dev.c:7738
 napi_poll net/core/dev.c:7801 [inline]
 net_rx_action+0x696/0xe00 net/core/dev.c:7958
 handle_softirqs+0x1de/0x6d0 kernel/softirq.c:626
 __do_softirq kernel/softirq.c:660 [inline]
 __local_bh_enable_ip+0x170/0x2b0 kernel/softirq.c:302
 local_bh_enable include/linux/bottom_half.h:33 [inline]
 netif_rx+0xb9/0xf0 net/core/dev.c:5776
 pn_send+0x62a/0x8e0 net/phonet/af_phonet.c:188
 pn_skb_send+0x218/0x530 net/phonet/af_phonet.c:275
 pipe_skb_send+0x2f7/0x540 net/phonet/pep.c:1130
 pep_sendmsg+0x9ca/0xb00 net/phonet/pep.c:1206
 pn_socket_sendmsg+0x1e5/0x250 net/phonet/socket.c:424
 sock_sendmsg_nosec+0x112/0x150 net/socket.c:797
 __sock_sendmsg net/socket.c:812 [inline]
 sock_write_iter+0x308/0x410 net/socket.c:1269
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x629/0xba0 fs/read_write.c:688
 ksys_write+0x156/0x270 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd74410c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fd743745028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fd744386090 RCX: 00007fd74410c819
RDX: 00000000000003db RSI: 0000200000000480 RDI: 0000000000000006
RBP: 00007fd7441a2c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fd744386128 R14: 00007fd744386090 R15: 00007fff7efc5418
 </TASK>