syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P8829/1:b..l
	(detected by 0, t=10503 jiffies, g=31741, q=59)
task:syz.3.1262      state:R  running task     stack:25072 pid: 8829 ppid:  4185 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:blk_cgroup_congested include/linux/blk-cgroup.h:285 [inline]
RIP: 0010:__cgroup_throttle_swaprate+0x245/0x530 mm/swapfile.c:3809
Code: 89 f7 e8 be 6f 06 00 4d 8b 36 4d 85 f6 0f 84 a9 00 00 00 e8 cd 63 c1 ff 41 bd 70 09 00 00 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 <74> 08 4c 89 f7 e8 91 6f 06 00 4d 8b 3e 4d 01 ef 4c 89 ff be 04 00
RSP: 0018:ffffc9000332f468 EFLAGS: 00000246
RAX: 1ffff11028f7fa00 RBX: 00fff00000080001 RCX: 0000000000080000
RDX: ffffc90004581000 RSI: 000000000007ffff RDI: 0000000000080000
RBP: 0000000000000001 R08: dffffc0000000000 R09: 1ffffffff203a618
R10: dffffc0000000000 R11: fffffbfff203a619 R12: dffffc0000000000
R13: 0000000000000970 R14: ffff888147bfd000 R15: ffff88802984002c
 cgroup_throttle_swaprate include/linux/swap.h:728 [inline]
 shmem_add_to_page_cache+0xb90/0x14d0 mm/shmem.c:727
 shmem_getpage_gfp+0x1796/0x2d40 mm/shmem.c:1940
 shmem_fault+0x1ac/0x540 mm/shmem.c:2118
 __do_fault+0x141/0x330 mm/memory.c:3928
 do_read_fault mm/memory.c:4264 [inline]
 do_fault mm/memory.c:4392 [inline]
 handle_pte_fault mm/memory.c:4650 [inline]
 __handle_mm_fault mm/memory.c:4785 [inline]
 handle_mm_fault+0x2985/0x4410 mm/memory.c:4883
 faultin_page mm/gup.c:976 [inline]
 __get_user_pages+0x94b/0x11e0 mm/gup.c:1197
 populate_vma_page_range+0x213/0x290 mm/gup.c:1529
 __mm_populate+0x275/0x3b0 mm/gup.c:1638
 mm_populate include/linux/mm.h:2646 [inline]
 vm_mmap_pgoff+0x212/0x2d0 mm/util.c:556
 ksys_mmap_pgoff+0x140/0x790 mm/mmap.c:1635
 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: 0033:0x7f37b8e2b629
RSP: 002b:00007f37b7085028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f37b90a4fa0 RCX: 00007f37b8e2b629
RDX: b635773f06ebbeee RSI: 0000000000b36000 RDI: 0000200000000000
RBP: 00007f37b8ec1b39 R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000008031 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f37b90a5038 R14: 00007f37b90a4fa0 R15: 00007ffe52d048f8
 </TASK>
rcu: rcu_preempt kthread starved for 10537 jiffies! g31741 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:27120 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:2117
 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: 8815 Comm: syz.2.1259 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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:2021
 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:__raw_spin_unlock_irq include/linux/spinlock_api_smp.h:169 [inline]
RIP: 0010:_raw_spin_unlock_irq+0x25/0x40 kernel/locking/spinlock.c:202
Code: 00 00 00 66 90 53 48 89 fb 48 83 c7 18 48 8b 74 24 08 e8 ee ea 97 f7 48 89 df e8 26 c3 98 f7 e8 91 b5 b9 f7 fb bf 01 00 00 00 <e8> a6 c9 8c f7 65 8b 05 47 d7 3c 76 85 c0 74 02 5b c3 e8 94 e4 3a
RSP: 0018:ffffc900031efbc0 EFLAGS: 00000282
RAX: d3b34fe78144cb00 RBX: ffff8880769e65c0 RCX: d3b34fe78144cb00
RDX: dffffc0000000000 RSI: ffffffff8a2b2780 RDI: 0000000000000001
RBP: 0000000000000000 R08: ffff8880769e65c3 R09: 1ffff1100ed3ccb8
R10: dffffc0000000000 R11: ffffed100ed3ccb9 R12: ffff8880769e65c0
R13: 0000000000000021 R14: dffffc0000000000 R15: 000000001c000004
 spin_unlock_irq include/linux/spinlock.h:414 [inline]
 get_signal+0x11d6/0x12c0 kernel/signal.c:2903
 arch_do_signal_or_restart+0xe7/0x12c0 arch/x86/kernel/signal.c:867
 handle_signal_work kernel/entry/common.c:154 [inline]
 exit_to_user_mode_loop+0x9e/0x130 kernel/entry/common.c:178
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f19bd112b86
Code: 1f 44 00 00 48 8b 70 f8 48 83 e8 08 48 39 f2 72 f3 48 39 c3 73 3e 48 89 33 48 89 c6 48 83 c3 08 48 89 08 48 8b 0b 48 8b 55 00 <eb> c0 48 39 f2 72 a4 48 39 f0 0f 83 c0 00 00 00 48 89 75 00 49 89
RSP: 002b:00007ffcd2594c40 EFLAGS: 00000212
RAX: 00007f19bd0201c0 RBX: 00007f19bcfa0610 RCX: ffffffff81d068db
RDX: ffffffff81d09099 RSI: 00007f19bd0201c0 RDI: 00007f19bcfe3238
RBP: 00007f19bcf99910 R08: 00007f19bd4a6000 R09: 00007f19bd4bc038
R10: 0000000000000001 R11: 0000000000000009 R12: 00007f19bd02cb68
R13: 000000000000001f R14: 000000000001264b R15: 0000000000000001
 </TASK>