syzbot

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1):
 P5889/1:b.el
 P5888/1:b..l

rcu: 	(detected by 1, t=10502 jiffies, g=10765, q=729 ncpus=2)
task:udevd           state:R
  running task     stack:26872 pid:5888  tgid:5888  ppid:5216   task_flags:0x400140 flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5397 [inline]
 __schedule+0x16f5/0x4d00 kernel/sched/core.c:6786
 preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7109
 irqentry_exit+0x6f/0x90 kernel/entry/common.c:307
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:__rcu_read_unlock+0x0/0xe0 kernel/rcu/tree_plugin.h:431
Code: 89 d9 80 e1 07 80 c1 03 38 c1 7c dc 48 89 df e8 66 56 7a 00 eb d2 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <f3> 0f 1e fa 41 57 41 56 41 55 41 54 53 49 bf 00 00 00 00 00 fc ff
RSP: 0018:ffffc900043bf170 EFLAGS: 00000282

RAX: b50a9f6cf8f45200 RBX: ffffffff90315e01 RCX: b50a9f6cf8f45200
RDX: 0000000000000000 RSI: ffffffff8db83fd2 RDI: ffffffff8be28d40
RBP: dffffc0000000000 R08: ffffc900043bf298 R09: 0000000000000000
R10: ffffc900043bf2f8 R11: fffff52000877e61 R12: ffffc900043bf2a8
R13: ffffc900043b8000 R14: ffffc900043bf2a8 R15: ffffffff8172aae5
 rcu_read_unlock include/linux/rcupdate.h:873 [inline]
 class_rcu_destructor include/linux/rcupdate.h:1155 [inline]
 unwind_next_frame+0x19ae/0x2390 arch/x86/kernel/unwind_orc.c:680
 __unwind_start+0x5b9/0x760 arch/x86/kernel/unwind_orc.c:758
 unwind_start arch/x86/include/asm/unwind.h:64 [inline]
 arch_stack_walk+0xe4/0x150 arch/x86/kernel/stacktrace.c:24
 stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
 unpoison_slab_object mm/kasan/common.c:319 [inline]
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:345
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4148 [inline]
 slab_alloc_node mm/slub.c:4197 [inline]
 kmem_cache_alloc_node_noprof+0x1bb/0x3c0 mm/slub.c:4249
 __alloc_skb+0x112/0x2d0 net/core/skbuff.c:660
 alloc_skb include/linux/skbuff.h:1336 [inline]
 alloc_skb_with_frags+0xca/0x890 net/core/skbuff.c:6665
 sock_alloc_send_pskb+0x857/0x990 net/core/sock.c:2999
 unix_dgram_sendmsg+0x451/0x17d0 net/unix/af_unix.c:2083
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg+0x219/0x270 net/socket.c:727
 sock_write_iter+0x258/0x330 net/socket.c:1131
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x548/0xa90 fs/read_write.c:686
 ksys_write+0x145/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f817b2a7407
RSP: 002b:00007ffcb3e46230 EFLAGS: 00000202
 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f817b94d880 RCX: 00007f817b2a7407
RDX: 0000000000000000 RSI: 00007ffcb3e462d7 RDI: 000000000000000a
RBP: 000000000000000a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 00007f817b94d6e8
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
task:udevd           state:R
  running task     stack:26440 pid:5889  tgid:5889  ppid:5216   task_flags:0x400140 flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5397 [inline]
 __schedule+0x16f5/0x4d00 kernel/sched/core.c:6786
 preempt_schedule_irq+0xb5/0x150 kernel/sched/core.c:7109
 irqentry_exit+0x6f/0x90 kernel/entry/common.c:307
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:rcu_is_watching+0x67/0xb0 kernel/rcu/tree.c:746
Code: 89 f7 e8 3c 0c 7b 00 48 c7 c3 58 ff a0 92 49 03 1e 48 89 d8 48 c1 e8 03 42 0f b6 04 38 84 c0 75 34 8b 03 65 ff 0d 69 a3 f8 10 <74> 11 83 e0 04 c1 e8 02 5b 41 5e 41 5f e9 c7 46 c9 09 cc e8 d1 79
RSP: 0018:ffffc900043cf880 EFLAGS: 00000286

RAX: 0000000000031844 RBX: ffff8880b8632f58 RCX: 32e8fcb877896200
RDX: ffff88807b230000 RSI: ffffffff8be28d20 RDI: ffffffff8be28ce0
RBP: 0000000000000001 R08: 0000000000000000 R09: ffffffff825be5ec
R10: dffffc0000000000 R11: ffffed102845c697 R12: dffffc0000000000
R13: 0000000000000001 R14: ffffffff8dbbcc70 R15: dffffc0000000000
 rcu_read_unlock include/linux/rcupdate.h:869 [inline]
 class_rcu_destructor include/linux/rcupdate.h:1155 [inline]
 kernfs_root+0x14e/0x230 fs/kernfs/kernfs-internal.h:80
 kernfs_root_is_locked fs/kernfs/kernfs-internal.h:109 [inline]
 kernfs_rcu_name fs/kernfs/kernfs-internal.h:119 [inline]
 kernfs_dop_revalidate+0x365/0x5d0 fs/kernfs/dir.c:1192
 d_revalidate fs/namei.c:929 [inline]
 lookup_fast+0x250/0x5b0 fs/namei.c:-1
 lookup_fast_for_open fs/namei.c:3754 [inline]
 open_last_lookups fs/namei.c:3787 [inline]
 path_openat+0x67e/0x3830 fs/namei.c:4052
 do_filp_open+0x1fa/0x410 fs/namei.c:4082
 do_sys_openat2+0x121/0x1c0 fs/open.c:1437
 do_sys_open fs/open.c:1452 [inline]
 __do_sys_openat fs/open.c:1468 [inline]
 __se_sys_openat fs/open.c:1463 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1463
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f817b2a7407
RSP: 002b:00007ffcb3e3f270 EFLAGS: 00000202 ORIG_RAX: 0000000000000101
RAX: ffffffffffffffda RBX: 00007f817b94d880 RCX: 00007f817b2a7407
RDX: 0000000000080000 RSI: 00007ffcb3e3f3a0 RDI: ffffffffffffff9c
RBP: 000055e37b56c060 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000202 R12: 000055e37b56c150
R13: 00007ffcb3e3f3a0 R14: 00007ffcb3e40801 R15: 00007ffcb3e40808
 </TASK>
rcu: rcu_preempt kthread starved for 4587 jiffies! g10765 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:27320 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5397 [inline]
 __schedule+0x16f5/0x4d00 kernel/sched/core.c:6786
 __schedule_loop kernel/sched/core.c:6864 [inline]
 schedule+0x165/0x360 kernel/sched/core.c:6879
 schedule_timeout+0x12b/0x270 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x301/0x1540 kernel/rcu/tree.c:2054
 rcu_gp_kthread+0x99/0x390 kernel/rcu/tree.c:2256
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
CPU: 1 UID: 0 PID: 5886 Comm: syz-executor417 Not tainted 6.16.0-rc6-syzkaller-00281-gf4a40a4282f4 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:csd_lock_wait kernel/smp.c:340 [inline]
RIP: 0010:smp_call_function_many_cond+0xf69/0x12d0 kernel/smp.c:885
Code: 00 45 8b 2f 44 89 ee 83 e6 01 31 ff e8 90 6e 0b 00 41 83 e5 01 49 bd 00 00 00 00 00 fc ff df 75 07 e8 3b 6a 0b 00 eb 37 f3 90 <43> 0f b6 04 2c 84 c0 75 10 41 f7 07 01 00 00 00 74 1e e8 20 6a 0b
RSP: 0018:ffffc900043af360 EFLAGS: 00000293

RAX: ffffffff81b4bd80 RBX: ffff8880b873b1c0 RCX: ffff888031795a00
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc900043af4c0 R08: ffffffff8fa1dcf7 R09: 1ffffffff1f43b9e
R10: dffffc0000000000 R11: fffffbfff1f43b9f R12: 1ffff110170c8385
R13: dffffc0000000000 R14: 0000000000000000 R15: ffff8880b8641c28
FS:  0000000000000000(0000) GS:ffff888125d23000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055e37b558060 CR3: 000000000df38000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 on_each_cpu_cond_mask+0x3f/0x80 kernel/smp.c:1052
 __flush_tlb_multi arch/x86/include/asm/paravirt.h:91 [inline]
 flush_tlb_multi arch/x86/mm/tlb.c:1361 [inline]
 flush_tlb_mm_range+0x6b1/0x12c0 arch/x86/mm/tlb.c:1451
 tlb_flush arch/x86/include/asm/tlb.h:23 [inline]
 tlb_flush_mmu_tlbonly include/asm-generic/tlb.h:490 [inline]
 tlb_flush_mmu+0x1a7/0x680 mm/mmu_gather.c:403
 tlb_finish_mmu+0xc3/0x1d0 mm/mmu_gather.c:497
 free_ldt_pgtables+0x17b/0x320 arch/x86/kernel/ldt.c:411
 arch_exit_mmap arch/x86/include/asm/mmu_context.h:234 [inline]
 exit_mmap+0x17c/0xb50 mm/mmap.c:1270
 __mmput+0x118/0x420 kernel/fork.c:1121
 exit_mm+0x1da/0x2c0 kernel/exit.c:581
 do_exit+0x648/0x22e0 kernel/exit.c:952
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1105
 get_signal+0x1286/0x1340 kernel/signal.c:3034
 arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:111
 exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
 do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f0f326c14db
Code: Unable to access opcode bytes at 0x7f0f326c14b1.
RSP: 002b:00007f0f32675180 EFLAGS: 00000246
 ORIG_RAX: 0000000000000010
RAX: fffffffffffffffc RBX: 00007f0f327494e0 RCX: 00007f0f326c14db
RDX: 00007f0f32675200 RSI: 0000000040085507 RDI: 0000000000000003
RBP: 00007f0f327493c0 R08: 0000000000000003 R09: 0000000000000081
R10: 0000000000000001 R11: 0000000000000246 R12: 00002000000002c0
R13: 00007f0f32716038 R14: 5fe4ebdcdcd7b73d R15: 00000000ffffff75
 </TASK>
sched: DL replenish lagged too much