linux-kernel - Re: [syzbot] [mm?] INFO: rcu detected stall in sys

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Message-ID: <696d73c8.a70a0220.34546f.0366.GAE@google.com>
Date: Sun, 18 Jan 2026 15:59:04 -0800
From: syzbot <syzbot+8bb3e2bee8a429cc76dd@...kaller.appspotmail.com>
To: kapoorarnav43@...il.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] INFO: rcu detected stall in sys_execve (6)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
INFO: rcu detected stall in worker_thread

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	1-...!: (1 GPs behind) idle=3fa4/1/0x4000000000000000 softirq=23801/23814 fqs=1
rcu: 	(detected by 0, t=10503 jiffies, g=17209, q=7435 ncpus=2)
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 5941 Comm: kworker/1:5 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events_power_efficient gc_worker
RIP: 0010:check_region_inline mm/kasan/generic.c:185 [inline]
RIP: 0010:kasan_check_range+0x19/0x2c0 mm/kasan/generic.c:200
Code: cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 55 41 57 41 56 41 55 41 54 53 b0 01 48 85 f6 0f 84 ba 01 00 00 <4c> 8d 04 37 49 39 f8 0f 82 82 02 00 00 49 b9 00 00 00 00 00 80 ff
RSP: 0018:ffffc90000a08ba8 EFLAGS: 00000002
RAX: 00000000ffffff01 RBX: ffffffff99b74750 RCX: ffffffff819e9061
RDX: 0000000000000001 RSI: 0000000000000004 RDI: ffffc90000a08c20
RBP: ffffc90000a08c98 R08: ffffffff99b74753 R09: 1ffffffff336e8ea
R10: dffffc0000000000 R11: fffffbfff336e8eb R12: ffffffff99b74760
R13: ffffffff99b74758 R14: 1ffffffff336e8ec R15: 1ffffffff336e8eb
FS:  0000000000000000(0000) GS:ffff888125f1e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff7a7c27432 CR3: 0000000073668000 CR4: 00000000003526f0
Call Trace:
 <IRQ>
 instrument_read_write include/linux/instrumented.h:54 [inline]
 atomic_try_cmpxchg_acquire include/linux/atomic/atomic-instrumented.h:1301 [inline]
 queued_spin_lock include/asm-generic/qspinlock.h:111 [inline]
 do_raw_spin_lock+0x121/0x290 kernel/locking/spinlock_debug.c:116
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:111 [inline]
 _raw_spin_lock_irqsave+0x4c/0x60 kernel/locking/spinlock.c:162
 debug_object_deactivate+0x6d/0x360 lib/debugobjects.c:873
 debug_hrtimer_deactivate kernel/time/hrtimer.c:443 [inline]
 debug_deactivate+0x1d/0x1e0 kernel/time/hrtimer.c:483
 __run_hrtimer kernel/time/hrtimer.c:1745 [inline]
 __hrtimer_run_queues+0x2b0/0xc30 kernel/time/hrtimer.c:1841
 hrtimer_interrupt+0x45b/0xaa0 kernel/time/hrtimer.c:1903
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1045 [inline]
 __sysvec_apic_timer_interrupt+0x102/0x3e0 arch/x86/kernel/apic/apic.c:1062
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1056
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:rcu_is_watching_curr_cpu include/linux/context_tracking.h:-1 [inline]
RIP: 0010:rcu_is_watching+0x44/0xb0 kernel/rcu/tree.c:751
Code: 73 65 49 bf 00 00 00 00 00 fc ff df 4c 8d 34 dd d0 0d 9b 8d 4c 89 f0 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 f7 e8 8c 1d 80 00 <48> c7 c3 d8 56 81 92 49 03 1e 48 89 d8 48 c1 e8 03 42 0f b6 04 38
RSP: 0018:ffffc90003d77860 EFLAGS: 00000246
RAX: 1ffffffff1b361bb RBX: 0000000000000001 RCX: 0000000080000001
RDX: 0000000000000000 RSI: ffffffff8bc086c0 RDI: ffffffff8bc08680
RBP: ffffffff8983265b R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff1f045cf R12: 0000000000000002
R13: ffffffff8df41aa0 R14: ffffffff8d9b0dd8 R15: dffffc0000000000
 trace_lock_acquire include/trace/events/lock.h:24 [inline]
 lock_acquire+0x5f/0x340 kernel/locking/lockdep.c:5831
 rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 rcu_read_lock include/linux/rcupdate.h:867 [inline]
 gc_worker+0x28c/0x13d0 net/netfilter/nf_conntrack_core.c:1546
 process_one_work kernel/workqueue.c:3257 [inline]
 process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
rcu: rcu_preempt kthread starved for 10479 jiffies! g17209 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:27416 pid:16    tgid:16    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5256 [inline]
 __schedule+0x149b/0x4fd0 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+0x510/0xa50 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:
CPU: 0 UID: 0 PID: 6390 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:csd_lock_wait kernel/smp.c:342 [inline]
RIP: 0010:smp_call_function_many_cond+0xcce/0x1260 kernel/smp.c:877
Code: 01 31 ff e8 d4 97 0b 00 41 83 e5 01 49 bd 00 00 00 00 00 fc ff df 75 07 e8 7f 93 0b 00 eb 38 f3 90 42 0f b6 04 2b 84 c0 75 11 <41> f7 04 24 01 00 00 00 74 1e e8 63 93 0b 00 eb e4 44 89 e1 80 e1
RSP: 0018:ffffc900031374a0 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 1ffff110170e8129 RCX: ffff8880254c9e80
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000000
RBP: ffffc900031375e0 R08: ffffffff8f822e77 R09: 1ffffffff1f045ce
R10: dffffc0000000000 R11: fffffbfff1f045cf R12: ffff8880b8740948
R13: dffffc0000000000 R14: ffff8880b863bb00 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888125e1e000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055fad049c6d8 CR3: 000000000dd3a000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 on_each_cpu_cond_mask+0x3f/0x80 kernel/smp.c:1043
 __flush_tlb_multi arch/x86/include/asm/paravirt.h:91 [inline]
 flush_tlb_multi arch/x86/mm/tlb.c:1382 [inline]
 flush_tlb_mm_range+0x60a/0x1170 arch/x86/mm/tlb.c:1472
 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+0x174/0xb10 mm/mmap.c:1263
 __mmput+0x118/0x430 kernel/fork.c:1173
 exit_mm+0x169/0x230 kernel/exit.c:581
 do_exit+0x627/0x22f0 kernel/exit.c:959
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1112
 get_signal+0x1285/0x1340 kernel/signal.c:3034
 arch_do_signal_or_restart+0x9a/0x7a0 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline]
 exit_to_user_mode_loop+0x87/0x4e0 kernel/entry/common.c:75
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline]
 do_syscall_64+0x2c1/0xf80 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f175fd915dc
Code: Unable to access opcode bytes at 0x7f175fd915b2.
RSP: 002b:00007ffd6bb31250 EFLAGS: 00000293 ORIG_RAX: 000000000000002c
RAX: 0000000000000040 RBX: 00007f1760b14620 RCX: 00007f175fd915dc
RDX: 0000000000000040 RSI: 00007f1760b14670 RDI: 0000000000000003
RBP: 0000000000000000 R08: 00007ffd6bb312a4 R09: 000000000000000c
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000003
R13: 0000000000000000 R14: 00007f1760b14670 R15: 0000000000000000
 </TASK>


Tested on:

commit:         f40ddcc0 Revert "nfc/nci: Add the inconsistency check ..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=16b06852580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=323fe5bdde2384a5
dashboard link: https://syzkaller.appspot.com/bug?extid=8bb3e2bee8a429cc76dd
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1688eb9a580000