syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P4424/1:b..l P5792/1:b..l
	(detected by 0, t=10502 jiffies, g=20237, q=69)
task:syz-executor    state:R  running task     stack:22000 pid: 5792 ppid:  5763 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
 preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6799
 irqentry_exit+0x63/0x70 kernel/entry/common.c:432
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x60 kernel/kcov.c:202
Code: 66 2e 0f 1f 84 00 00 00 00 00 53 48 89 fb e8 17 00 00 00 48 8b 3d d0 48 10 0c 48 89 de 5b e9 67 3a 44 00 00 00 cc cc 00 00 cc <48> 8b 04 24 65 48 8b 0d 64 5f 89 7e 65 8b 15 65 5f 89 7e 81 e2 00
RSP: 0018:ffffc90003c8f900 EFLAGS: 00000283
RAX: 0000000000000001 RBX: ffffc90003c8fd40 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: ffffc90003c8f9f0 RDI: ffffc90003c8fd40
RBP: 0000000000000ffd R08: ffffc90003c8f9ff R09: ffffc90003c8f9f0
R10: dffffc0000000000 R11: fffff52000791f40 R12: 0000000000001000
R13: dffffc0000000000 R14: ffff88807c308ffd R15: 0000000000000ffe
 rcu_lock_acquire+0x5/0x30 include/linux/rcupdate.h:312
 rcu_read_lock include/linux/rcupdate.h:740 [inline]
 prepend_path+0x2f/0xbb0 fs/d_path.c:165
 d_absolute_path+0x9e/0x140 fs/d_path.c:235
 tomoyo_get_absolute_path security/tomoyo/realpath.c:101 [inline]
 tomoyo_realpath_from_path+0x331/0x610 security/tomoyo/realpath.c:276
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_perm+0x23f/0x5d0 security/tomoyo/file.c:822
 tomoyo_path_unlink+0xa7/0xf0 security/tomoyo/tomoyo.c:149
 security_path_unlink+0xd8/0x130 security/security.c:1170
 do_unlinkat+0x2fc/0x710 fs/namei.c:4352
 __do_sys_unlink fs/namei.c:4404 [inline]
 __se_sys_unlink fs/namei.c:4402 [inline]
 __x64_sys_unlink+0x45/0x50 fs/namei.c:4402
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7ff8d55bcda7
RSP: 002b:00007ffeba09ef98 EFLAGS: 00000202 ORIG_RAX: 0000000000000057
RAX: ffffffffffffffda RBX: 0000000000001101 RCX: 00007ff8d55bcda7
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00007ffeba09f050
RBP: 00007ffeba09f050 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007ffeba0a0140
R13: 00007ff8d562771f R14: 000055557717e4e8 R15: 0000000000000006
 </TASK>
task:udevd           state:R  running task     stack:23216 pid: 4424 ppid:  3560 flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
 preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6571
 preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6596
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
 __raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
 _raw_spin_unlock_irq+0x3c/0x40 kernel/locking/spinlock.c:202
 spin_unlock_irq include/linux/spinlock.h:414 [inline]
 loop_queue_work drivers/block/loop.c:1069 [inline]
 loop_queue_rq+0x9e0/0xac0 drivers/block/loop.c:2202
 __blk_mq_issue_directly block/blk-mq.c:2014 [inline]
 __blk_mq_try_issue_directly+0x497/0x820 block/blk-mq.c:2070
 blk_mq_request_issue_directly block/blk-mq.c:2118 [inline]
 blk_mq_try_issue_list_directly+0x1a1/0x530 block/blk-mq.c:2136
 blk_mq_sched_insert_requests+0x2d6/0x5c0 block/blk-mq-sched.c:512
 blk_mq_flush_plug_list+0x59b/0x690 block/blk-mq.c:1971
 blk_flush_plug_list+0x404/0x450 block/blk-core.c:1734
 blk_finish_plug+0x59/0x80 block/blk-core.c:1751
 read_pages+0x4d2/0x930 mm/readahead.c:150
 page_cache_ra_unbounded+0x838/0x940 mm/readahead.c:239
 do_page_cache_ra mm/readahead.c:269 [inline]
 force_page_cache_ra+0x3e5/0x440 mm/readahead.c:301
 page_cache_sync_readahead include/linux/pagemap.h:833 [inline]
 filemap_get_pages mm/filemap.c:2551 [inline]
 filemap_read+0x5de/0x2540 mm/filemap.c:2634
 blkdev_read_iter+0x11d/0x150 block/fops.c:563
 call_read_iter include/linux/fs.h:2167 [inline]
 new_sync_read fs/read_write.c:404 [inline]
 vfs_read+0x759/0xd60 fs/read_write.c:485
 ksys_read+0x152/0x260 fs/read_write.c:623
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f3b87c24407
RSP: 002b:00007ffe91c12da0 EFLAGS: 00000202 ORIG_RAX: 0000000000000000
RAX: ffffffffffffffda RBX: 00007f3b87b36880 RCX: 00007f3b87c24407
RDX: 0000000000000200 RSI: 00007f3b871d7000 RDI: 0000000000000009
RBP: 0000556dc528d260 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 0000000000000000
R13: 0000000000000000 R14: 0000556dc527d578 R15: 00007f3b8837a39c
 </TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 10413 jiffies! g20237 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=0 timer-softirq=9040
rcu: rcu_preempt kthread starved for 10419 jiffies! g20237 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->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:I stack:27536 pid:   15 ppid:     2 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11ef/0x43c0 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0x184/0x2d0 kernel/time/timer.c:1914
 rcu_gp_fqs_loop+0x2be/0x11d0 kernel/rcu/tree.c:1972
 rcu_gp_kthread+0x9b/0x370 kernel/rcu/tree.c:2145
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
 rcu_check_gp_kthread_starvation+0x1cd/0x250 kernel/rcu/tree_stall.h:487
 print_other_cpu_stall+0x1110/0x1270 kernel/rcu/tree_stall.h:592
 check_cpu_stall kernel/rcu/tree_stall.h:745 [inline]
 rcu_pending kernel/rcu/tree.c:3936 [inline]
 rcu_sched_clock_irq+0x843/0x1120 kernel/rcu/tree.c:2619
 update_process_times+0x193/0x200 kernel/time/timer.c:1818
 tick_sched_handle kernel/time/tick-sched.c:254 [inline]
 tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4ad/0xb70 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x3bb/0x8d0 kernel/time/hrtimer.c:1811
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
 __sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0x9b/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:default_idle+0xb/0x10 arch/x86/kernel/process.c:730
Code: b7 48 89 df e8 c6 9c fa f7 eb ad e8 4f b1 f6 ff 00 00 cc cc 00 00 cc cc 00 00 cc cc 00 00 cc 66 90 0f 00 2d 67 4c 62 00 fb f4 <c3> 0f 1f 40 00 41 57 41 56 53 49 be 00 00 00 00 00 fc ff df 65 48
RSP: 0018:ffffffff8c007dc8 EFLAGS: 000002c6
RAX: 478d45f7c6612e00 RBX: ffffffff8c0bc480 RCX: 478d45f7c6612e00
RDX: 0000000000000001 RSI: ffffffff8a2b1c00 RDI: ffffffff8a79e740
RBP: ffffffff8c007ef8 R08: ffff8880b903b30b R09: 1ffff11017207661
R10: dffffc0000000000 R11: ffffed1017207662 R12: 1ffffffff1817890
R13: dffffc0000000000 R14: 0000000000000000 R15: 1ffffffff1800fc4
 default_idle_call+0x81/0xc0 kernel/sched/idle.c:112
 cpuidle_idle_call kernel/sched/idle.c:194 [inline]
 do_idle+0x21f/0x580 kernel/sched/idle.c:306
 cpu_startup_entry+0x14/0x20 kernel/sched/idle.c:403
 start_kernel+0x489/0x540 init/main.c:1154
 secondary_startup_64_no_verify+0xb1/0xbb
 </TASK>
vkms_vblank_simulate: vblank timer overrun