INFO: rcu detected stall in debug_check_no_obj_freed

Status: upstream: reported syz repro on 2026/09/19 17:50
Reported-by: syzbot+565c2fb0d9cd17ab0f64@syzkaller.appspotmail.com
First crash: 1d17h, last: 1d17h
Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream BUG: soft lockup in debug_check_no_obj_freed serial 1 syz 2 701d 701d 0/29 auto-obsoleted due to no activity on 2025/01/27 15:36
linux-6.6 INFO: rcu detected stall in debug_check_no_obj_freed origin:lts-only 1 syz, C error 1 282d 314d 0/2 upstream: reported C repro on 2025/11/11 10:45
linux-5.15 INFO: rcu detected stall in debug_check_no_obj_freed origin:lts-only 1 syz error 2 176d 315d 0/3 upstream: reported syz repro on 2025/11/10 02:51
upstream INFO: rcu detected stall in debug_check_no_obj_freed fs 1 1 596d 596d 0/29 auto-obsoleted due to no activity on 2025/05/03 06:53
upstream BUG: soft lockup in debug_check_no_obj_freed (2) kernel 1 1 288d 288d 0/29 closed as invalid on 2026/01/09 17:04

Sample crash report:
rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2670 jiffies s: 3813 root: 0x1/.
rcu: blocking rcu_node structures (internal RCU debug):
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 4407 Comm: syz-executor Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:asm_sysvec_irq_work+0x0/0x20 arch/x86/include/asm/idtentry.h:722
Code: e9 b5 03 00 00 90 90 90 90 90 0f 01 ca fc 6a ff e8 b5 02 00 00 48 89 c4 48 89 e7 e8 aa 53 f2 ff e9 95 03 00 00 90 90 90 90 90 <0f> 01 ca fc 6a ff e8 95 02 00 00 48 89 c4 48 89 e7 e8 7a 58 f2 ff
RSP: 0018:ffffc900000079d8 EFLAGS: 00000006
RAX: f24fac2fcc045800 RBX: 1ffff92000000f48 RCX: f24fac2fcc045800
RDX: dffffc0000000000 RSI: ffffffff8a8c18a0 RDI: ffffffff8adf68a0
RBP: ffffc90000007b00 R08: ffff8880b8e357cb R09: 1ffff110171c6af9
R10: dffffc0000000000 R11: ffffed10171c6afa R12: 0000000000000246
R13: dffffc0000000000 R14: ffff8880b8e3bb00 R15: 0000000000000001
FS:  0000555576566500(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555576581a38 CR3: 0000000054a7c000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
RIP: 0010:rcu_read_unlock_special+0x7f/0x510 kernel/rcu/tree_plugin.h:685
Code: eb 03 48 b8 f1 f1 f1 f1 f8 f2 f2 f2 4a 89 04 2b 42 c7 44 2b 08 f8 f3 f3 f3 65 44 8b 35 32 7b 95 7e 41 f7 c6 00 00 f0 00 74 40 <48> c7 44 24 40 0e 36 e0 45 4a c7 04 2b 00 00 00 00 42 c7 44 2b 08
RSP: 0018:ffffc90000007a00 EFLAGS: 00000206
 __rcu_read_unlock+0x78/0xd0 kernel/rcu/tree_plugin.h:426
 rcu_read_unlock include/linux/rcupdate.h:823 [inline]
 process_backlog+0x3ff/0x710 net/core/dev.c:6062
 __napi_poll+0xbb/0x460 net/core/dev.c:6628
 napi_poll net/core/dev.c:6695 [inline]
 net_rx_action+0x622/0xbc0 net/core/dev.c:6809
 handle_softirqs+0x291/0x910 kernel/softirq.c:596
 __do_softirq kernel/softirq.c:630 [inline]
 invoke_softirq kernel/softirq.c:470 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:679
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1118 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1118
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xbc/0x120 kernel/locking/spinlock.c:194
Code: c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f7 44 24 20 00 02 00 00 41 c6 04 07 f8 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> 3f 1a 1c f7 65 8b 05 10 ca c5 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc900041d7bc0 EFLAGS: 00000206
RAX: dffffc0000000004 RBX: 0000000000000a06 RCX: f24fac2fcc045800
RDX: dffffc0000000000 RSI: ffffffff8a8c18a0 RDI: 0000000000000001
RBP: ffffc900041d7c50 R08: ffff8880b8e357cb R09: 1ffff110171c6af9
R10: dffffc0000000000 R11: ffffed10171c6afa R12: dffffc0000000000
R13: ffff8880183b4f30 R14: ffffffff96ec3e20 R15: 1ffff9200083af78
 __debug_check_no_obj_freed lib/debugobjects.c:1054 [inline]
 debug_check_no_obj_freed+0x471/0x520 lib/debugobjects.c:1075
 slab_free_hook mm/slub.c:1704 [inline]
 slab_free_freelist_hook+0xd2/0x1b0 mm/slub.c:1755
 slab_free mm/slub.c:3687 [inline]
 kmem_cache_free+0xf7/0x2a0 mm/slub.c:3709
 file_free fs/file_table.c:56 [inline]
 __fput+0x5cb/0x8b0 fs/file_table.c:333
 task_work_run+0x1d0/0x260 kernel/task_work.c:203
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:180
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:213
 __syscall_exit_to_user_mode_work kernel/entry/common.c:295 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:306
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fba1db5e98e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007ffd178ca018 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: 0000000000000000 RBX: 0000555576566500 RCX: 00007fba1db5e98e
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007ffd178ca0bc R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000001a
R13: 00000000000927c0 R14: 00000000000236de R15: 00007ffd178ca110
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/19 17:50 linux-6.1.y 1a8763b93150 853b104b .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in debug_check_no_obj_freed
* Struck through repros no longer work on HEAD.