====================================================== WARNING: possible circular locking dependency detected syzkaller #0 Not tainted ------------------------------------------------------ syz.0.664/8554 is trying to acquire lock: ffff888061e6d160 (slock-AF_PHONET/1){+.+.}-{3:3}, at: __sk_receive_skb+0x1bf/0x9e0 net/core/sock.c:563 but task is already holding lock: ffff8880352762e0 (slock-AF_PHONET){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline] ffff8880352762e0 (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:6203 [inline] __netif_receive_skb net/core/dev.c:6316 [inline] process_backlog+0x5e1/0xc60 net/core/dev.c:6667 __napi_poll+0xab/0x550 net/core/dev.c:7731 napi_poll net/core/dev.c:7794 [inline] net_rx_action+0x696/0xe00 net/core/dev.c:7951 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:309 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+0x15a5/0x2d10 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:6203 [inline] __netif_receive_skb net/core/dev.c:6316 [inline] process_backlog+0x5e1/0xc60 net/core/dev.c:6667 __napi_poll+0xab/0x550 net/core/dev.c:7731 napi_poll net/core/dev.c:7794 [inline] net_rx_action+0x696/0xe00 net/core/dev.c:7951 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_sock_close+0x2c1/0x5b0 include/linux/skbuff.h:-1 pn_socket_release+0x9b/0xc0 net/phonet/socket.c:34 __sock_release+0xb9/0x250 net/socket.c:726 sock_close+0x1c/0x30 net/socket.c:1529 __fput+0x461/0xa70 fs/file_table.c:510 task_work_run+0x1d9/0x270 kernel/task_work.c:233 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] __exit_to_user_mode_loop kernel/entry/common.c:67 [inline] exit_to_user_mode_loop+0xf3/0x4d0 kernel/entry/common.c:98 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline] do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100 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 *** 7 locks held by syz.0.664/8554: #0: ffff88805f6816f8 (&sb->s_type->i_mutex_key#13){+.+.}-{4:4}, at: inode_lock include/linux/fs.h:1029 [inline] #0: ffff88805f6816f8 (&sb->s_type->i_mutex_key#13){+.+.}-{4:4}, at: __sock_release+0x89/0x250 net/socket.c:725 #1: ffff888035275ad8 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1713 [inline] #1: ffff888035275ad8 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: pep_sock_close+0x86/0x5b0 net/phonet/pep.c:742 #2: ffffffff8dfc8240 (rcu_read_lock){....}-{1:3}, at: __local_bh_disable_ip+0x3c/0x420 kernel/softirq.c:163 #3: ffffffff8dfc8240 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline] #3: ffffffff8dfc8240 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline] #3: ffffffff8dfc8240 (rcu_read_lock){....}-{1:3}, at: process_backlog+0x271/0xc60 net/core/dev.c:6666 #4: ffff8880352762e0 (slock-AF_PHONET){+...}-{3:3}, at: spin_lock include/linux/spinlock_rt.h:45 [inline] #4: ffff8880352762e0 (slock-AF_PHONET){+...}-{3:3}, at: __sk_receive_skb+0x1f1/0x9e0 net/core/sock.c:565 #5: ffffffff8dfc8240 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline] #5: ffffffff8dfc8240 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline] #5: ffffffff8dfc8240 (rcu_read_lock){....}-{1:3}, at: __rt_spin_lock kernel/locking/spinlock_rt.c:50 [inline] #5: ffffffff8dfc8240 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1e0/0x400 kernel/locking/spinlock_rt.c:57 #6: ffff888035276398 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: sk_receive_skb include/net/sock.h:2022 [inline] #6: ffff888035276398 (sk_lock-AF_PHONET){+.+.}-{0:0}, at: phonet_rcv+0x781/0xc40 net/phonet/af_phonet.c:-1 stack backtrace: CPU: 0 UID: 0 PID: 8554 Comm: syz.0.664 Not tainted syzkaller #0 PREEMPT_{RT,(full)} Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026 Call Trace: 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+0x15a5/0x2d10 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:6203 [inline] __netif_receive_skb net/core/dev.c:6316 [inline] process_backlog+0x5e1/0xc60 net/core/dev.c:6667 __napi_poll+0xab/0x550 net/core/dev.c:7731 napi_poll net/core/dev.c:7794 [inline] net_rx_action+0x696/0xe00 net/core/dev.c:7951 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_sock_close+0x2c1/0x5b0 include/linux/skbuff.h:-1 pn_socket_release+0x9b/0xc0 net/phonet/socket.c:34 __sock_release+0xb9/0x250 net/socket.c:726 sock_close+0x1c/0x30 net/socket.c:1529 __fput+0x461/0xa70 fs/file_table.c:510 task_work_run+0x1d9/0x270 kernel/task_work.c:233 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] __exit_to_user_mode_loop kernel/entry/common.c:67 [inline] exit_to_user_mode_loop+0xf3/0x4d0 kernel/entry/common.c:98 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline] do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fc1eac2cdd9 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:00007ffe12e8fb08 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 00007fc1eaea7da0 RCX: 00007fc1eac2cdd9 RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003 RBP: 00007fc1eaea7da0 R08: 0000000000000006 R09: 0000000000000000 R10: 00007fc1eaea7cb0 R11: 0000000000000246 R12: 0000000000062e71 R13: 00007fc1eaea609c R14: 0000000000062bb6 R15: 00007ffe12e8fc10