[v6.6] INFO: rcu detected stall in sys_clone

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 3a8ababb8b6a Linux 6.6.101
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=17f38c34580000
kernel config: https://syzkaller.appspot.com/x/.config?x=a2bd95b6de4839b7
dashboard link: https://syzkaller.appspot.com/bug?extid=4a0c2a1f63c5084ccdd9
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ae2055ece513/disk-3a8ababb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/72f91e4de841/vmlinux-3a8ababb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3dae292c190e/bzImage-3a8ababb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4a0c2a...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 0-....: (10499 ticks this GP) idle=b21c/1/0x4000000000000000 softirq=34016/556508 fqs=5128
rcu: hardirqs softirqs csw/system
rcu: number: 3360693 267186 0
rcu: cputime: 31828 19998 654 ==> 52490(ms)
rcu: (t=10500 jiffies g=38621 q=1849 ncpus=2)
CPU: 0 PID: 9870 Comm: syz.2.1368 Not tainted 6.6.101-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x60 kernel/kcov.c:212
Code: 00 0f 0b 0f 1f 80 00 00 00 00 f3 0f 1e fa 53 48 89 fb e8 13 00 00 00 48 8b 3d 8c f1 c4 0c 48 89 de 5b e9 63 75 56 00 cc cc cc <f3> 0f 1e fa 48 8b 04 24 65 48 8b 0d 60 24 7e 7e 65 8b 15 61 24 7e
RSP: 0018:ffffc90000007490 EFLAGS: 00000206
RAX: 0000000000000014 RBX: 0000005163e611ca RCX: ffff8880241d8000
RDX: 0000000000000100 RSI: ffffffff8cd79100 RDI: 0000000000000004
RBP: 0000000000000848 R08: ffff8880241d8000 R09: 0000000000000020
R10: 000000000000001f R11: 0000000000000100 R12: 0000000000000294
R13: f800000000000000 R14: 0000000000000294 R15: 0000005163e67b5e
FS: 00007fb5376346c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2e517ff8 CR3: 0000000026532000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
<IRQ>
check_buffer+0x556/0x950 kernel/trace/ring_buffer.c:3491
__rb_reserve_next+0x511/0xd50 kernel/trace/ring_buffer.c:3624
rb_reserve_next_event kernel/trace/ring_buffer.c:3759 [inline]
ring_buffer_lock_reserve+0xae1/0xed0 kernel/trace/ring_buffer.c:3818
__trace_buffer_lock_reserve kernel/trace/trace.c:992 [inline]
trace_event_buffer_lock_reserve+0x1d0/0x6e0 kernel/trace/trace.c:2902
trace_event_buffer_reserve+0x29b/0x3c0 kernel/trace/trace_events.c:661
do_trace_event_raw_event_bpf_trace_printk kernel/trace/bpf_trace.h:11 [inline]
trace_event_raw_event_bpf_trace_printk+0x101/0x210 kernel/trace/bpf_trace.h:11
trace_bpf_trace_printk+0x142/0x1a0 kernel/trace/bpf_trace.h:11
____bpf_trace_printk kernel/trace/bpf_trace.c:388 [inline]
bpf_trace_printk+0x11f/0x190 kernel/trace/bpf_trace.c:371
bpf_prog_0605f9f479290f07+0x37/0x3b
bpf_dispatcher_nop_func include/linux/bpf.h:1213 [inline]
__bpf_prog_run include/linux/filter.h:612 [inline]
bpf_prog_run include/linux/filter.h:619 [inline]
__bpf_trace_run kernel/trace/bpf_trace.c:2322 [inline]
bpf_trace_run1+0x1c9/0x3b0 kernel/trace/bpf_trace.c:2360
__bpf_trace_rcu_utilization+0xa2/0xe0 include/trace/events/rcu.h:27
trace_rcu_utilization+0x179/0x1a0 include/trace/events/rcu.h:27
rcu_core+0x1341/0x1720 kernel/rcu/tree.c:2475
handle_softirqs+0x280/0x820 kernel/softirq.c:578
__do_softirq kernel/softirq.c:612 [inline]
invoke_softirq kernel/softirq.c:452 [inline]
__irq_exit_rcu+0xc7/0x190 kernel/softirq.c:661
irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
instr_sysvec_irq_work arch/x86/kernel/irq_work.c:17 [inline]
sysvec_irq_work+0xa1/0xc0 arch/x86/kernel/irq_work.c:17
</IRQ>
<TASK>
asm_sysvec_irq_work+0x1a/0x20 arch/x86/include/asm/idtentry.h:723
RIP: 0010:preempt_schedule_irq+0xb0/0x140 kernel/sched/core.c:7010
Code: 44 24 20 f6 44 24 21 02 74 0b 0f 0b 48 f7 03 08 00 00 00 74 63 bf 01 00 00 00 e8 cb 12 e6 f6 e8 16 99 16 f7 fb bf 01 00 00 00 <e8> db b5 ff ff 48 c7 44 24 40 00 00 00 00 9c 8f 44 24 40 8b 44 24
RSP: 0018:ffffc900193bf520 EFLAGS: 00000282
RAX: f3b7c3e1c75b9500 RBX: 0000000000000000 RCX: f3b7c3e1c75b9500
RDX: dffffc0000000000 RSI: ffffffff8aaaba40 RDI: 0000000000000001
RBP: ffffc900193bf5c0 R08: ffffffff90da35cf R09: 1ffffffff21b46b9
R10: dffffc0000000000 R11: fffffbfff21b46ba R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff92003277ea4
irqentry_exit+0x67/0x70 kernel/entry/common.c:438
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:lock_release+0x57c/0x8b0 kernel/locking/lockdep.c:5778
Code: 00 00 00 00 9c 8f 84 24 80 00 00 00 f6 84 24 81 00 00 00 02 75 75 f7 44 24 50 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 2f 00 00 00 00 66 43 c7 44 2f 09 00 00 43 c6 44 2f 0b 00
RSP: 0018:ffffc900193bf680 EFLAGS: 00000206
RAX: 0000000000000001 RBX: c097c23dfe07078d RCX: f3b7c3e1c75b9500
RDX: 0000000000000003 RSI: ffffffff8aaacbc0 RDI: ffffffff8afc6780
RBP: ffffc900193bf798 R08: ffffffff8e4a84ef R09: 1ffffffff1c9509d
R10: dffffc0000000000 R11: fffffbfff1c9509e R12: ffff8880241d8b58
R13: dffffc0000000000 R14: ffff8880241d8ad0 R15: 1ffff92003277edc
up_write+0x2d/0x410 kernel/locking/rwsem.c:1625
vma_start_write include/linux/mm.h:730 [inline]
dup_userfaultfd+0x270/0x800 fs/userfaultfd.c:695
dup_mmap kernel/fork.c:723 [inline]
dup_mm kernel/fork.c:1692 [inline]
copy_mm+0xcb3/0x1c20 kernel/fork.c:1741
copy_process+0x16d3/0x3d70 kernel/fork.c:2506
kernel_clone+0x21b/0x840 kernel/fork.c:2914
__do_sys_clone kernel/fork.c:3057 [inline]
__se_sys_clone kernel/fork.c:3041 [inline]
__x64_sys_clone+0x18c/0x1e0 kernel/fork.c:3041
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fb53678ebe9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fb537633fe8 EFLAGS: 00000206 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 00007fb5369b5fa0 RCX: 00007fb53678ebe9
RDX: 00002000000006c0 RSI: 0000000000000000 RDI: 0000000001001200
RBP: 00007fb536811e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000206 R12: 0000000000000000
R13: 00007fb5369b6038 R14: 00007fb5369b5fa0 R15: 00007ffd6d1a5008
</TASK>


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: bb9c90ab9c5a Linux 6.6.102
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=147cc462580000
kernel config: https://syzkaller.appspot.com/x/.config?x=7b989b97a0687b0a

dashboard link: https://syzkaller.appspot.com/bug?extid=4a0c2a1f63c5084ccdd9
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=166e9c42580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=137d6462580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3741b512b75a/disk-bb9c90ab.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/dedce7f4c998/vmlinux-bb9c90ab.xz
kernel image: https://storage.googleapis.com/syzbot-assets/acd529da0064/bzImage-bb9c90ab.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+4a0c2a...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 0-....: (1 GPs behind) idle=7564/1/0x4000000000000000 softirq=25979/25981 fqs=2100
rcu: hardirqs softirqs csw/system
rcu: number: 12023821 0 0
rcu: cputime: 6233 46283 0 ==> 52500(ms)
rcu: (detected by 1, t=10505 jiffies, g=18593, q=226 ncpus=2)
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 6758 Comm: syz-executor355 Not tainted 6.6.102-syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025

RIP: 0010:check_kcov_mode kernel/kcov.c:182 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:245 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp8+0x2e/0x80 kernel/kcov.c:320
Code: 48 8b 04 24 65 48 8b 0d 90 2a 7e 7e 65 8b 15 91 2a 7e 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 57 83 b9 1c 16 00 00 00 <74> 4e 8b 91 f8 15 00 00 83 fa 03 75 43 48 8b 91 00 16 00 00 44 8b
RSP: 0018:ffffc90000006dd8 EFLAGS: 00000046
RAX: ffffffff81ac3d31 RBX: 0000000000000010 RCX: ffff88801e6cbc00
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc90000006ed0 R08: dffffc0000000000 R09: 1ffffffff21b46a0
R10: dffffc0000000000 R11: fffffbfff21b46a1 R12: ffffc900000071c0
R13: dffffc0000000000 R14: 0000000000000500 R15: 0000000000000010
FS: 0000555572be3380(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 000020000000014c CR3: 0000000018fb6000 CR4: 00000000003506f0
Call Trace:
<IRQ>
perf_prepare_sample+0x13a1/0x1c40 kernel/events/core.c:7907
__perf_event_output kernel/events/core.c:7971 [inline]
perf_event_output_forward+0x152/0x3a0 kernel/events/core.c:7992
__perf_event_overflow+0x447/0x630 kernel/events/core.c:9717
perf_swevent_overflow kernel/events/core.c:9793 [inline]
perf_swevent_event+0x2f5/0x5c0 kernel/events/core.c:-1
perf_tp_event+0x4f9/0x13a0 kernel/events/core.c:10343
perf_trace_run_bpf_submit+0xf4/0x1c0 kernel/events/core.c:10267
perf_trace_preemptirq_template+0x281/0x340 include/trace/events/preemptirq.h:14
trace_irq_enable+0xbf/0xe0 include/trace/events/preemptirq.h:40
trace_hardirqs_on+0x18/0x40 kernel/trace/trace_preemptirq.c:56
asm_sysvec_irq_work+0x1a/0x20 arch/x86/include/asm/idtentry.h:723
RIP: 0010:rcu_read_unlock_special+0x88/0x4c0 kernel/rcu/tree_plugin.h:682
Code: f1 f1 f1 00 f2 f2 f2 4a 89 04 2b 66 42 c7 44 2b 09 f3 f3 42 c6 44 2b 0b f3 65 44 8b 35 39 58 93 7e 41 f7 c6 00 00 f0 00 74 45 <48> c7 44 24 40 0e 36 e0 45 4a c7 04 2b 00 00 00 00 66 42 c7 44 2b
RSP: 0018:ffffc900000075c0 EFLAGS: 00000206
RAX: 6b2189b8c1a9d800 RBX: 1ffff92000000ec0 RCX: 6b2189b8c1a9d800
RDX: dffffc0000000000 RSI: ffffffff8aaab9c0 RDI: ffffffff8afc66c0
RBP: ffffc900000076a8 R08: ffffffff90da350f R09: 1ffffffff21b46a1
R10: dffffc0000000000 R11: fffffbfff21b46a2 R12: ffffffff8cd35400
R13: dffffc0000000000 R14: 0000000000000246 R15: 0000000000000001
__rcu_read_unlock+0x7c/0xd0 kernel/rcu/tree_plugin.h:426
rcu_read_unlock include/linux/rcupdate.h:818 [inline]
is_bpf_text_address+0x27e/0x2a0 kernel/bpf/core.c:743
kernel_text_address+0xa0/0xd0 kernel/extable.c:125
__kernel_text_address+0xd/0x30 kernel/extable.c:79
unwind_get_return_address+0x5d/0xc0 arch/x86/kernel/unwind_orc.c:369
arch_stack_walk+0x11d/0x190 arch/x86/kernel/stacktrace.c:26
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
kasan_save_free_info+0x2e/0x50 mm/kasan/generic.c:522
____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:236
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1806 [inline]
slab_free_freelist_hook+0x130/0x1b0 mm/slub.c:1832
slab_free mm/slub.c:3816 [inline]
kmem_cache_free+0xf8/0x280 mm/slub.c:3838
rcu_do_batch kernel/rcu/tree.c:2194 [inline]
rcu_core+0xcc4/0x1720 kernel/rcu/tree.c:2467

handle_softirqs+0x280/0x820 kernel/softirq.c:578
__do_softirq kernel/softirq.c:612 [inline]
invoke_softirq kernel/softirq.c:452 [inline]
__irq_exit_rcu+0xc7/0x190 kernel/softirq.c:661
irq_exit_rcu+0x9/0x20 kernel/softirq.c:673

instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:__orc_find arch/x86/kernel/unwind_orc.c:102 [inline]
RIP: 0010:orc_find arch/x86/kernel/unwind_orc.c:227 [inline]
RIP: 0010:unwind_next_frame+0x4b8/0x2970 arch/x86/kernel/unwind_orc.c:494
Code: 01 c8 48 83 e0 fe 4d 8d 3c 44 4c 89 f8 48 c1 e8 03 0f b6 04 10 84 c0 75 3e 4d 63 2f 4d 01 fd 4c 89 ef 4c 89 f6 e8 b8 e5 4a 00 <49> 8d 47 04 4d 39 f5 4c 0f 46 e0 49 8d 47 fc 48 0f 47 d8 49 0f 46
RSP: 0018:ffffc9000b947078 EFLAGS: 00000293
RAX: ffffffff813aa778 RBX: ffffffff8e624728 RCX: ffff88801e6cbc00
RDX: 0000000000000000 RSI: ffffffff81dbf44d RDI: ffffffff81dbf449
RBP: ffffffff8e624724 R08: ffffc9000b947210 R09: 0000000000000003
R10: 0000000000000004 R11: 0000000000000000 R12: ffffffff8e624728
R13: ffffffff81dbf449 R14: ffffffff81dbf44d R15: ffffffff8e624728
arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
kasan_save_stack mm/kasan/common.c:45 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:328
kasan_slab_alloc include/linux/kasan.h:188 [inline]
slab_post_alloc_hook+0x6e/0x4d0 mm/slab.h:767
slab_alloc_node mm/slub.c:3485 [inline]
slab_alloc mm/slub.c:3493 [inline]
__kmem_cache_alloc_lru mm/slub.c:3500 [inline]
kmem_cache_alloc+0x11e/0x2e0 mm/slub.c:3509
kmem_cache_zalloc include/linux/slab.h:711 [inline]
__proc_create+0x370/0x8d0 fs/proc/generic.c:425
proc_create_reg+0x8b/0x110 fs/proc/generic.c:552
proc_create_net_data+0x99/0x1b0 fs/proc/proc_net.c:120
ping_v6_proc_init_net+0x59/0x70 net/ipv6/ping.c:259
ops_init+0x397/0x640 net/core/net_namespace.c:139
setup_net+0x3a5/0xa00 net/core/net_namespace.c:343
copy_net_ns+0x36d/0x5e0 net/core/net_namespace.c:520
create_new_namespaces+0x3d3/0x6f0 kernel/nsproxy.c:110
copy_namespaces+0x430/0x4a0 kernel/nsproxy.c:179
copy_process+0x1700/0x3d70 kernel/fork.c:2509

kernel_clone+0x21b/0x840 kernel/fork.c:2914
__do_sys_clone kernel/fork.c:3057 [inline]
__se_sys_clone kernel/fork.c:3041 [inline]
__x64_sys_clone+0x18c/0x1e0 kernel/fork.c:3041
do_syscall_x64 arch/x86/entry/common.c:51 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:81
entry_SYSCALL_64_after_hwframe+0x68/0xd2

RIP: 0033:0x7f59721e7ab9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 c1 17 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc26107018 EFLAGS: 00000246 ORIG_RAX: 0000000000000038
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f59721e7ab9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00000000e50c1600
RBP: 0000000000032541 R08: 0000000000000000 R09: 0000000000000006
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffc2610702c
R13: 431bde82d7b634db R14: 0000000000000001 R15: 0000000000000001
</TASK>
INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 3.994 msecs


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

[syzbot]

syzbot suspects this issue was fixed by commit:

commit e7a375453cca2b8a0d2fa1b82b913f3fed7c0507
Author: Joel Fernandes <joela...@nvidia.com>
Date: Tue Jul 8 14:22:19 2025 +0000

rcu: Fix rcu_read_unlock() deadloop due to IRQ work

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=169bbc1a580000
start commit: bb9c90ab9c5a Linux 6.6.102
git tree: linux-6.6.y

kernel config: https://syzkaller.appspot.com/x/.config?x=7b989b97a0687b0a
dashboard link: https://syzkaller.appspot.com/bug?extid=4a0c2a1f63c5084ccdd9

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=166e9c42580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=137d6462580000

If the result looks correct, please mark the issue as fixed by replying with:

#syz fix: rcu: Fix rcu_read_unlock() deadloop due to IRQ work

For information about bisection process see: https://goo.gl/tpsmEJ#bisection