syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P5454/1:b..l
rcu: 	(detected by 0, t=10502 jiffies, g=6961, q=12 ncpus=2)
task:dhcpcd          state:R  running task     stack:21032 pid:5454  ppid:5453   flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5380 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
 preempt_schedule_irq+0xb5/0x140 kernel/sched/core.c:7009
 irqentry_exit+0x67/0x70 kernel/entry/common.c:438
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:__wake_up_common_lock kernel/sched/wait.c:141 [inline]
RIP: 0010:__wake_up_sync_key+0x11f/0x190 kernel/sched/wait.c:213
Code: 89 c4 4c 89 ff 89 de 44 89 ea b9 10 00 00 00 4d 89 f0 4c 8d 4c 24 40 e8 9f f8 ff ff 41 89 c5 4c 89 ff 4c 89 e6 e8 a1 4e 13 09 <f6> 44 24 40 04 75 c6 49 bc 00 00 00 00 00 fc ff df 48 8b 44 24 18
RSP: 0018:ffffc90003667780 EFLAGS: 00010246
RAX: efe498b98e8e1300 RBX: 0000000000000001 RCX: 0000000000000000
RDX: dffffc0000000000 RSI: ffffffff8aaabca0 RDI: 00000000ffffffff
RBP: ffffc90003667878 R08: ffffffff8e4a94ef R09: 1ffffffff1c9529d
R10: dffffc0000000000 R11: fffffbfff1c9529e R12: 0000000000000a02
R13: 0000000000000001 R14: 00000000000000c3 R15: ffff888148cb1840
 sock_def_readable+0x1e1/0x430 net/core/sock.c:3346
 unix_dgram_sendmsg+0x10cc/0x1720 net/unix/af_unix.c:2141
 sock_sendmsg_nosec net/socket.c:730 [inline]
 __sock_sendmsg net/socket.c:745 [inline]
 sock_write_iter+0x2bb/0x3f0 net/socket.c:1160
 do_iter_readv_writev fs/read_write.c:-1 [inline]
 do_iter_write+0x79a/0xc70 fs/read_write.c:860
 vfs_writev fs/read_write.c:933 [inline]
 do_writev+0x252/0x410 fs/read_write.c:976
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f7684cc9407
RSP: 002b:00007ffd3aa79550 EFLAGS: 00000202 ORIG_RAX: 0000000000000014
RAX: ffffffffffffffda RBX: 00007f7684c3f740 RCX: 00007f7684cc9407
RDX: 0000000000000002 RSI: 00007ffd3aa795f0 RDI: 000000000000000b
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 000000000000000b
R13: 00007f7684c3f6c8 R14: 0000000000000000 R15: 00007ffd3aa89700
 </TASK>
rcu: rcu_preempt kthread starved for 10538 jiffies! g6961 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=1
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:27752 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5380 [inline]
 __schedule+0x14d2/0x44d0 kernel/sched/core.c:6699
 preempt_schedule_irq+0xb5/0x140 kernel/sched/core.c:7009
 irqentry_exit+0x67/0x70 kernel/entry/common.c:438
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:__timer_delete_sync+0x191/0x2c0 kernel/time/timer.c:1563
Code: 61 10 00 49 89 dc 4d 85 f6 48 bb 00 00 00 00 00 fc ff df 75 07 e8 df 61 10 00 eb 06 e8 d8 61 10 00 fb 65 44 8b 35 97 8b 8e 7e <44> 89 f6 81 e6 00 00 0f 00 31 ff e8 6f 65 10 00 41 81 e6 00 00 0f
RSP: 0018:ffffc90000167aa0 EFLAGS: 00000293
RAX: ffffffff81752e68 RBX: dffffc0000000000 RCX: ffff88801be50000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000167b70 R08: ffffffff8e4a94ef R09: 1ffffffff1c9529d
R10: dffffc0000000000 R11: fffffbfff1c9529e R12: ffffc90000167ba0
R13: 1ffff9200002cf58 R14: 0000000080000000 R15: 0000000000000000
 timer_delete_sync kernel/time/timer.c:1628 [inline]
 del_timer_sync include/linux/timer.h:200 [inline]
 schedule_timeout+0x16a/0x280 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x302/0x1560 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x99/0x380 kernel/rcu/tree.c:1866
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 5797 Comm: syz-executor195 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:entry_SYSCALL_64_after_hwframe+0x59/0xd2
Code: 45 31 e4 45 31 ed 45 31 f6 45 31 ff 48 89 e7 48 63 f0 66 90 b9 48 00 00 00 65 48 8b 14 25 60 7f 02 00 89 d0 48 c1 ea 20 0f 30 <0f> 1f 44 00 00 e8 d5 19 00 00 e8 c0 cf ed ff 0f 1f 44 00 00 48 8b
RSP: 0018:ffffc9000461ff58 EFLAGS: 00000046
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 0000000000000048
RDX: 0000000000000000 RSI: 000000000000000f RDI: ffffc9000461ff58
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f4b44f586c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000058 CR3: 000000007426e000 CR4: 00000000003506e0
Call Trace:
 <TASK>
RIP: 0033:0x7f4b44f6ac89
Code: 64 c7 00 16 00 00 00 b8 ff ff ff ff c3 0f 1f 40 00 90 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 c7 c0 0f 00 00 00 0f 05 <0f> 1f 80 00 00 00 00 48 81 ec 48 01 00 00 49 89 d0 64 48 8b 04 25
RSP: 002b:00007f4b44f57bc0 EFLAGS: 00000202 ORIG_RAX: 000000000000000f
RAX: ffffffffffffffda RBX: 00007f4b45022308 RCX: 00007f4b44f6ac89
RDX: 00007f4b44f57bc0 RSI: 00007f4b44f57cf0 RDI: 0000000000000021
RBP: 00007f4b45022300 R08: 00007f4b44f586c0 R09: 00007f4b44f586c0
R10: 0000000000000000 R11: 0000000000000202 R12: 00007f4b4502230c
R13: 0000000000000000 R14: 00007ffd3a710f90 R15: 00007ffd3a711078
 </TASK>