[v6.6] INFO: rcu detected stall in task_mm_cid_work
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syzbot
Dec 19, 2025, 3:11:30 PM12/19/25
to syzkaller...@googlegroups.com
Hello,
syzbot found the following issue on:
HEAD commit: 5fa4793a2d2d Linux 6.6.119
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1580377c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=691a6769a86ac817
dashboard link: https://syzkaller.appspot.com/bug?extid=df63b3cfac01eabd92ee
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1528e984580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1482fdc2580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/857fe583cdec/disk-5fa4793a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ed4d3c1402bc/vmlinux-5fa4793a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/40296d968c3d/bzImage-5fa4793a.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+df63b3...@syzkaller.appspotmail.com
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 1-....: (7636 ticks this GP) idle=8ccc/1/0x4000000000000000 softirq=12954/12965 fqs=5247
rcu: hardirqs softirqs csw/system
rcu: number: 1528861 62 0
rcu: cputime: 16126 36353 37 ==> 52500(ms)
rcu: (t=10502 jiffies g=9473 q=2211 ncpus=2)
CPU: 1 PID: 5989 Comm: syz.1.18 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:check_kcov_mode kernel/kcov.c:182 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x27/0x60 kernel/kcov.c:216
Code: cc cc cc f3 0f 1e fa 48 8b 04 24 65 48 8b 0d f0 24 7e 7e 65 8b 15 f1 24 7e 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 35 <83> b9 1c 16 00 00 00 74 2c 8b 91 f8 15 00 00 83 fa 02 75 21 48 8b
RSP: 0018:ffffc900001ef9d0 EFLAGS: 00000246
RAX: ffffffff813aa367 RBX: ffffc900001efb60 RCX: ffff88801f3c3c00
RDX: 0000000000000100 RSI: ffffffff81e6251d RDI: ffffc900001efaa8
RBP: ffffc900001efb30 R08: ffffc900001efb70 R09: 0000000000000000
R10: 0000000000000004 R11: 0000000000000100 R12: ffffc900001efaa8
R13: dffffc0000000000 R14: ffffffff81746d20 R15: ffffc900001efaa8
FS: 0000555592ce6500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055c9685d3468 CR3: 00000000731b3000 CR4: 00000000003506e0
Call Trace:
<IRQ>
unwind_next_frame+0x27/0x2970 arch/x86/kernel/unwind_orc.c:469
arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
save_stack+0xf7/0x1f0 mm/page_owner.c:128
__set_page_owner+0x1d/0x60 mm/page_owner.c:192
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x1cd/0x210 mm/page_alloc.c:1554
prep_new_page mm/page_alloc.c:1561 [inline]
get_page_from_freelist+0x195c/0x19f0 mm/page_alloc.c:3191
__alloc_pages+0x1e3/0x460 mm/page_alloc.c:4457
alloc_slab_page+0x5d/0x170 mm/slub.c:1881
allocate_slab mm/slub.c:2028 [inline]
new_slab+0x87/0x2e0 mm/slub.c:2081
___slab_alloc+0xc6d/0x1300 mm/slub.c:3253
__slab_alloc mm/slub.c:3339 [inline]
__slab_alloc_node mm/slub.c:3392 [inline]
slab_alloc_node mm/slub.c:3485 [inline]
slab_alloc mm/slub.c:3503 [inline]
__kmem_cache_alloc_lru mm/slub.c:3510 [inline]
kmem_cache_alloc+0x1b7/0x2e0 mm/slub.c:3519
skb_clone+0x1eb/0x370 net/core/skbuff.c:1915
deliver_clone net/bridge/br_forward.c:125 [inline]
maybe_deliver+0x98/0x150 net/bridge/br_forward.c:191
br_flood+0x31b/0x680 net/bridge/br_forward.c:237
br_dev_xmit+0x1176/0x17f0 net/bridge/br_device.c:106
__netdev_start_xmit include/linux/netdevice.h:4943 [inline]
netdev_start_xmit include/linux/netdevice.h:4957 [inline]
xmit_one net/core/dev.c:3619 [inline]
dev_hard_start_xmit+0x246/0x740 net/core/dev.c:3635
__dev_queue_xmit+0x1a64/0x35a0 net/core/dev.c:4425
dev_queue_xmit include/linux/netdevice.h:3113 [inline]
neigh_hh_output include/net/neighbour.h:527 [inline]
neigh_output include/net/neighbour.h:541 [inline]
ip6_finish_output2+0xdf5/0x1650 net/ipv6/ip6_output.c:141
dst_output include/net/dst.h:467 [inline]
NF_HOOK include/linux/netfilter.h:304 [inline]
ndisc_send_skb+0xbed/0x14b0 net/ipv6/ndisc.c:513
addrconf_rs_timer+0x2bc/0x600 net/ipv6/addrconf.c:4006
call_timer_fn+0x16e/0x530 kernel/time/timer.c:1701
expire_timers kernel/time/timer.c:1752 [inline]
__run_timers+0x52d/0x7d0 kernel/time/timer.c:2023
run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
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:preempt_schedule_irq+0xb0/0x140 kernel/sched/core.c:7009
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 8b b3 eb f6 e8 26 3a 1c 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:ffffc90003517840 EFLAGS: 00000286
RAX: 763624262c051a00 RBX: 0000000000000000 RCX: 763624262c051a00
RDX: dffffc0000000000 RSI: ffffffff8aaabce0 RDI: 0000000000000001
RBP: ffffc900035178e0 R08: ffffffff8e4a212f R09: 1ffffffff1c94425
R10: dffffc0000000000 R11: fffffbfff1c94426 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff920006a2f08
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_acquire+0x1f2/0x410 kernel/locking/lockdep.c:5758
Code: 00 9c 8f 84 24 80 00 00 00 f6 84 24 81 00 00 00 02 0f 85 f5 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 3c 00 00 00 00 66 43 c7 44 3c 09 00 00 43 c6 44 3c 0b 00
RSP: 0018:ffffc900035179a0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 763624262c051a00
RDX: 0000000000000000 RSI: ffffffff8aaace60 RDI: ffffffff8afc6f80
RBP: ffffc90003517aa8 R08: dffffc0000000000 R09: 1ffffffff21b28a0
R10: dffffc0000000000 R11: fffffbfff21b28a1 R12: 1ffff920006a2f40
R13: ffffffff8cd2ff20 R14: 0000000000000246 R15: dffffc0000000000
rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
rcu_read_lock include/linux/rcupdate.h:786 [inline]
sched_mm_cid_remote_clear_old kernel/sched/core.c:11933 [inline]
task_mm_cid_work+0x335/0x760 kernel/sched/core.c:11994
task_work_run+0x1ce/0x250 kernel/task_work.c:239
get_signal+0x1235/0x1400 kernel/signal.c:2678
arch_do_signal_or_restart+0x9c/0x7b0 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xf6/0x180 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:87
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f6f0138f749
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:00007fffeb0bc8a8 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
RAX: 0000000000000004 RBX: 00007f6f015e5fa0 RCX: 00007f6f0138f749
RDX: ffffffffffffffff RSI: 0000000000000000 RDI: 0000200000000140
RBP: 00007f6f01413f91 R08: 0000000000000002 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6f015e5fa0 R14: 00007f6f015e5fa0 R15: 0000000000000005
</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 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.
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 found the following issue on:
HEAD commit: 5fa4793a2d2d Linux 6.6.119
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=1580377c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=691a6769a86ac817
dashboard link: https://syzkaller.appspot.com/bug?extid=df63b3cfac01eabd92ee
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1528e984580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1482fdc2580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/857fe583cdec/disk-5fa4793a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ed4d3c1402bc/vmlinux-5fa4793a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/40296d968c3d/bzImage-5fa4793a.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+df63b3...@syzkaller.appspotmail.com
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 1-....: (7636 ticks this GP) idle=8ccc/1/0x4000000000000000 softirq=12954/12965 fqs=5247
rcu: hardirqs softirqs csw/system
rcu: number: 1528861 62 0
rcu: cputime: 16126 36353 37 ==> 52500(ms)
rcu: (t=10502 jiffies g=9473 q=2211 ncpus=2)
CPU: 1 PID: 5989 Comm: syz.1.18 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:check_kcov_mode kernel/kcov.c:182 [inline]
RIP: 0010:__sanitizer_cov_trace_pc+0x27/0x60 kernel/kcov.c:216
Code: cc cc cc f3 0f 1e fa 48 8b 04 24 65 48 8b 0d f0 24 7e 7e 65 8b 15 f1 24 7e 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 35 <83> b9 1c 16 00 00 00 74 2c 8b 91 f8 15 00 00 83 fa 02 75 21 48 8b
RSP: 0018:ffffc900001ef9d0 EFLAGS: 00000246
RAX: ffffffff813aa367 RBX: ffffc900001efb60 RCX: ffff88801f3c3c00
RDX: 0000000000000100 RSI: ffffffff81e6251d RDI: ffffc900001efaa8
RBP: ffffc900001efb30 R08: ffffc900001efb70 R09: 0000000000000000
R10: 0000000000000004 R11: 0000000000000100 R12: ffffc900001efaa8
R13: dffffc0000000000 R14: ffffffff81746d20 R15: ffffc900001efaa8
FS: 0000555592ce6500(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055c9685d3468 CR3: 00000000731b3000 CR4: 00000000003506e0
Call Trace:
<IRQ>
unwind_next_frame+0x27/0x2970 arch/x86/kernel/unwind_orc.c:469
arch_stack_walk+0x144/0x190 arch/x86/kernel/stacktrace.c:25
stack_trace_save+0x9c/0xe0 kernel/stacktrace.c:122
save_stack+0xf7/0x1f0 mm/page_owner.c:128
__set_page_owner+0x1d/0x60 mm/page_owner.c:192
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x1cd/0x210 mm/page_alloc.c:1554
prep_new_page mm/page_alloc.c:1561 [inline]
get_page_from_freelist+0x195c/0x19f0 mm/page_alloc.c:3191
__alloc_pages+0x1e3/0x460 mm/page_alloc.c:4457
alloc_slab_page+0x5d/0x170 mm/slub.c:1881
allocate_slab mm/slub.c:2028 [inline]
new_slab+0x87/0x2e0 mm/slub.c:2081
___slab_alloc+0xc6d/0x1300 mm/slub.c:3253
__slab_alloc mm/slub.c:3339 [inline]
__slab_alloc_node mm/slub.c:3392 [inline]
slab_alloc_node mm/slub.c:3485 [inline]
slab_alloc mm/slub.c:3503 [inline]
__kmem_cache_alloc_lru mm/slub.c:3510 [inline]
kmem_cache_alloc+0x1b7/0x2e0 mm/slub.c:3519
skb_clone+0x1eb/0x370 net/core/skbuff.c:1915
deliver_clone net/bridge/br_forward.c:125 [inline]
maybe_deliver+0x98/0x150 net/bridge/br_forward.c:191
br_flood+0x31b/0x680 net/bridge/br_forward.c:237
br_dev_xmit+0x1176/0x17f0 net/bridge/br_device.c:106
__netdev_start_xmit include/linux/netdevice.h:4943 [inline]
netdev_start_xmit include/linux/netdevice.h:4957 [inline]
xmit_one net/core/dev.c:3619 [inline]
dev_hard_start_xmit+0x246/0x740 net/core/dev.c:3635
__dev_queue_xmit+0x1a64/0x35a0 net/core/dev.c:4425
dev_queue_xmit include/linux/netdevice.h:3113 [inline]
neigh_hh_output include/net/neighbour.h:527 [inline]
neigh_output include/net/neighbour.h:541 [inline]
ip6_finish_output2+0xdf5/0x1650 net/ipv6/ip6_output.c:141
dst_output include/net/dst.h:467 [inline]
NF_HOOK include/linux/netfilter.h:304 [inline]
ndisc_send_skb+0xbed/0x14b0 net/ipv6/ndisc.c:513
addrconf_rs_timer+0x2bc/0x600 net/ipv6/addrconf.c:4006
call_timer_fn+0x16e/0x530 kernel/time/timer.c:1701
expire_timers kernel/time/timer.c:1752 [inline]
__run_timers+0x52d/0x7d0 kernel/time/timer.c:2023
run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
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:preempt_schedule_irq+0xb0/0x140 kernel/sched/core.c:7009
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 8b b3 eb f6 e8 26 3a 1c 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:ffffc90003517840 EFLAGS: 00000286
RAX: 763624262c051a00 RBX: 0000000000000000 RCX: 763624262c051a00
RDX: dffffc0000000000 RSI: ffffffff8aaabce0 RDI: 0000000000000001
RBP: ffffc900035178e0 R08: ffffffff8e4a212f R09: 1ffffffff1c94425
R10: dffffc0000000000 R11: fffffbfff1c94426 R12: 0000000000000000
R13: 0000000000000000 R14: dffffc0000000000 R15: 1ffff920006a2f08
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_acquire+0x1f2/0x410 kernel/locking/lockdep.c:5758
Code: 00 9c 8f 84 24 80 00 00 00 f6 84 24 81 00 00 00 02 0f 85 f5 00 00 00 41 f7 c6 00 02 00 00 74 01 fb 48 c7 44 24 60 0e 36 e0 45 <4b> c7 04 3c 00 00 00 00 66 43 c7 44 3c 09 00 00 43 c6 44 3c 0b 00
RSP: 0018:ffffc900035179a0 EFLAGS: 00000206
RAX: 0000000000000001 RBX: 0000000000000000 RCX: 763624262c051a00
RDX: 0000000000000000 RSI: ffffffff8aaace60 RDI: ffffffff8afc6f80
RBP: ffffc90003517aa8 R08: dffffc0000000000 R09: 1ffffffff21b28a0
R10: dffffc0000000000 R11: fffffbfff21b28a1 R12: 1ffff920006a2f40
R13: ffffffff8cd2ff20 R14: 0000000000000246 R15: dffffc0000000000
rcu_lock_acquire include/linux/rcupdate.h:334 [inline]
rcu_read_lock include/linux/rcupdate.h:786 [inline]
sched_mm_cid_remote_clear_old kernel/sched/core.c:11933 [inline]
task_mm_cid_work+0x335/0x760 kernel/sched/core.c:11994
task_work_run+0x1ce/0x250 kernel/task_work.c:239
get_signal+0x1235/0x1400 kernel/signal.c:2678
arch_do_signal_or_restart+0x9c/0x7b0 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xf6/0x180 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:87
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f6f0138f749
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:00007fffeb0bc8a8 EFLAGS: 00000246 ORIG_RAX: 000000000000012a
RAX: 0000000000000004 RBX: 00007f6f015e5fa0 RCX: 00007f6f0138f749
RDX: ffffffffffffffff RSI: 0000000000000000 RDI: 0000200000000140
RBP: 00007f6f01413f91 R08: 0000000000000002 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007f6f015e5fa0 R14: 00007f6f015e5fa0 R15: 0000000000000005
</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 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.
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
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