====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ ksoftirqd/1/30 is trying to acquire lock: ffff888061f4d160 (slock-AF_PHONET/1){+.+.}-{3:3}, at: __sk_receive_skb+0x1bf/0x9e0 net/core/sock.c:563 but task is already holding lock: ffff888061f4e2e0 (slock-AF_PHONET){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline] ffff888061f4e2e0 (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:6209 [inline] __netif_receive_skb net/core/dev.c:6322 [inline] process_backlog+0x5e1/0xc60 net/core/dev.c:6673 __napi_poll+0xab/0x550 net/core/dev.c:7737 napi_poll net/core/dev.c:7800 [inline] net_rx_action+0x696/0xe00 net/core/dev.c:7957 handle_softirqs+0x1de/0x6d0 kernel/softirq.c:622 __do_softirq kernel/softirq.c:656 [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:5775 pn_send+0x62a/0x8e0 net/phonet/af_phonet.c:188 pn_skb_send+0x218/0x510 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+0x52b/0x760 net/socket.c:2047 __sys_accept4_file net/socket.c:2081 [inline] __sys_accept4+0x139/0x230 net/socket.c:2103 __do_sys_accept4 net/socket.c:2110 [inline] __se_sys_accept4 net/socket.c:2107 [inline] __x64_sys_accept4+0x9a/0xb0 net/socket.c:2107 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:3165 [inline] check_prevs_add kernel/locking/lockdep.c:3284 [inline] validate_chain kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868 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:6209 [inline] __netif_receive_skb net/core/dev.c:6322 [inline] process_backlog+0x5e1/0xc60 net/core/dev.c:6673 __napi_poll+0xab/0x550 net/core/dev.c:7737 napi_poll net/core/dev.c:7800 [inline] net_rx_action+0x696/0xe00 net/core/dev.c:7957 handle_softirqs+0x1de/0x6d0 kernel/softirq.c:622 run_ksoftirqd+0x52/0x180 kernel/softirq.c:1076 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160 kthread+0x388/0x470 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 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 ksoftirqd/1/30: #0: ffffffff8de5f2c0 (local_bh){.+.+}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163 #1: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163 #2: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline] #2: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline] #2: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: process_backlog+0x271/0xc60 net/core/dev.c:6672 #3: ffff888061f4e2e0 (slock-AF_PHONET){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline] #3: ffff888061f4e2e0 (slock-AF_PHONET){+...}-{3:3}, at: __sk_receive_skb+0x1f1/0x9e0 net/core/sock.c:565 #4: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline] #4: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline] #4: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline] #4: ffffffff8dfc80c0 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1e0/0x400 kernel/locking/spinlock_rt.c:57 #5: ffff888061f4e398 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: sk_receive_skb include/net/sock.h:2022 [inline] #5: ffff888061f4e398 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: phonet_rcv+0x781/0xc40 net/phonet/af_phonet.c:-1 stack backtrace: CPU: 1 UID: 0 PID: 30 Comm: ksoftirqd/1 Not tainted syzkaller #0 PREEMPT_{RT,(full)} Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026 Call Trace: dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_circular_bug+0x2e1/0x300 kernel/locking/lockdep.c:2043 check_noncircular+0x12e/0x150 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 kernel/locking/lockdep.c:3908 [inline] __lock_acquire+0x15a5/0x2cf0 kernel/locking/lockdep.c:5237 lock_acquire+0x106/0x350 kernel/locking/lockdep.c:5868 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:6209 [inline] __netif_receive_skb net/core/dev.c:6322 [inline] process_backlog+0x5e1/0xc60 net/core/dev.c:6673 __napi_poll+0xab/0x550 net/core/dev.c:7737 napi_poll net/core/dev.c:7800 [inline] net_rx_action+0x696/0xe00 net/core/dev.c:7957 handle_softirqs+0x1de/0x6d0 kernel/softirq.c:622 run_ksoftirqd+0x52/0x180 kernel/softirq.c:1076 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160 kthread+0x388/0x470 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245