syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P5964/2:b..l
rcu: 	(detected by 1, t=10503 jiffies, g=11745, q=1315 ncpus=2)
task:syz-executor    state:R  running task     stack:19496 pid:5964  tgid:5964  ppid:5953   task_flags:0x400140 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6863
 preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7190
 irqentry_exit+0x5d8/0x660 kernel/entry/common.c:216
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:is_anon_ns fs/mount.h:179 [inline]
RIP: 0010:__prepend_path fs/d_path.c:122 [inline]
RIP: 0010:prepend_path+0x580/0x830 fs/d_path.c:172
Code: 95 c0 48 81 fb 01 f0 ff ff 0f 92 c1 84 c8 75 07 e8 35 ac 77 ff eb 21 48 81 c3 6c 01 00 00 48 89 d8 48 c1 e8 03 42 0f b6 04 30 <84> c0 75 44 80 3b 00 74 13 e8 12 ac 77 ff 41 bc 02 00 00 00 45 31
RSP: 0018:ffffc900032e78d8 EFLAGS: 00000a07
RAX: 0000000000000000 RBX: ffff888031cb496c RCX: ffff88802b8fdb01
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff88807b04f6d0
RBP: ffffc900032e79a8 R08: ffffffff8fc3a577 R09: 1ffffffff1f874ae
R10: dffffc0000000000 R11: fffffbfff1f874af R12: ffff888149000178
R13: ffff8881490001c8 R14: dffffc0000000000 R15: ffff88807b04f6c0
 d_absolute_path+0xa1/0x140 fs/d_path.c:234
 tomoyo_get_absolute_path security/tomoyo/realpath.c:101 [inline]
 tomoyo_realpath_from_path+0x2c8/0x5d0 security/tomoyo/realpath.c:271
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_perm+0x213/0x4b0 security/tomoyo/file.c:822
 tomoyo_sb_umount+0x9c/0xe0 security/tomoyo/tomoyo.c:430
 security_sb_umount+0xbb/0x290 security/security.c:1076
 do_umount fs/namespace.c:1866 [inline]
 path_umount+0x36e/0xb40 fs/namespace.c:2038
 ksys_umount fs/namespace.c:2061 [inline]
 __do_sys_umount fs/namespace.c:2066 [inline]
 __se_sys_umount fs/namespace.c:2064 [inline]
 __x64_sys_umount+0x122/0x160 fs/namespace.c:2064
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f776f190a77
RSP: 002b:00007ffc4d8fcc88 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: ffffffffffffffda RBX: 00007f776f2143a5 RCX: 00007f776f190a77
RDX: 00007f776f18de97 RSI: 0000000000000002 RDI: 00007f776f214631
RBP: 00007f776f2145d9 R08: 0000000000000000 R09: 00007ffc4d8fcd00
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f776f1ef400
R13: 00007f776f1ef3d8 R14: 00007ffc4d8fcf88 R15: 0000000000000000
 </TASK>
rcu: rcu_preempt kthread starved for 10233 jiffies! g11745 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
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:27304 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x14bc/0x5000 kernel/sched/core.c:6863
 __schedule_loop kernel/sched/core.c:6945 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6960
 schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2083
 rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2285
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 6117 Comm: syz.1.33 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:check_kcov_mode kernel/kcov.c:194 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:246 [inline]
RIP: 0010:__sanitizer_cov_trace_cmp8+0x37/0x90 kernel/kcov.c:294
Code: 08 30 c3 92 65 8b 15 28 3a 01 11 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 57 83 b9 6c 16 00 00 00 74 4e 8b 91 48 16 00 00 <83> fa 03 75 43 48 8b 91 50 16 00 00 44 8b 89 4c 16 00 00 49 c1 e1
RSP: 0018:ffffc900038076d8 EFLAGS: 00000246
RAX: ffffffff8241d762 RBX: ffff888034578648 RCX: ffff88802f09db80
RDX: 0000000000000000 RSI: 7fffffffffffffff RDI: 000000006934818d
RBP: ffffc90003807798 R08: ffffffff8fc3a577 R09: 1ffffffff1f874ae
R10: dffffc0000000000 R11: fffffbfff1f874af R12: 7fffffffffffffff
R13: 8000000000000000 R14: 000000006934818d R15: 0000000000000001
FS:  00007f13c39676c0(0000) GS:ffff8881259ed000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f88948bcf98 CR3: 0000000073140000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 timestamp_truncate fs/inode.c:2763 [inline]
 current_time+0x1c2/0x360 fs/inode.c:2358
 file_update_time_flags+0xcd/0x4e0 fs/inode.c:2375
 shmem_file_write_iter+0xcf/0x120 mm/shmem.c:3487
 iter_file_splice_write+0x972/0x10b0 fs/splice.c:738
 do_splice_from fs/splice.c:938 [inline]
 direct_splice_actor+0x101/0x160 fs/splice.c:1161
 splice_direct_to_actor+0x5a8/0xcc0 fs/splice.c:1105
 do_splice_direct_actor fs/splice.c:1204 [inline]
 do_splice_direct+0x181/0x270 fs/splice.c:1230
 do_sendfile+0x4da/0x7e0 fs/read_write.c:1370
 __do_sys_sendfile64 fs/read_write.c:1431 [inline]
 __se_sys_sendfile64+0x13e/0x190 fs/read_write.c:1417
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f13c2b8f749
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:00007f13c3967038 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f13c2de5fa0 RCX: 00007f13c2b8f749
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000003
RBP: 00007f13c2c13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0001000000201005 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f13c2de6038 R14: 00007f13c2de5fa0 R15: 00007ffd05b60108
 </TASK>