[v5.15] INFO: rcu detected stall in sys_mlock (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c86c4726e7f0 Linux 5.15.211
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=12f1a0b9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=6f8e2266b61925dc
dashboard link: https://syzkaller.appspot.com/bug?extid=6d18e493d35a61aea34b
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15f71b89580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=15865346580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c3e980557785/disk-c86c4726.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5fbaf3714ad0/vmlinux-c86c4726.xz
kernel image: https://storage.googleapis.com/syzbot-assets/de60a4f1e940/bzImage-c86c4726.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/addcbd061b11/mount_3.gz
fsck result: failed (log: https://syzkaller.appspot.com/x/fsck.log?x=11f71b89580000)

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6d18e4...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
(detected by 0, t=10502 jiffies, g=6209, q=8)
rcu: All QSes seen, last rcu_preempt kthread activity 10502 (4294959109-4294948607), jiffies_till_next_fqs=1, root ->qsmask 0x0
rcu: rcu_preempt kthread starved for 10502 jiffies! g6209 f0x2 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:28240 pid: 15 ppid: 2 flags:0x00004000
Call Trace:
<TASK>
context_switch kernel/sched/core.c:5049 [inline]
__schedule+0x11c3/0x4350 kernel/sched/core.c:6395
schedule+0x11b/0x1e0 kernel/sched/core.c:6478
schedule_timeout+0x184/0x2d0 kernel/time/timer.c:2117
rcu_gp_fqs_loop+0x2be/0x11f0 kernel/rcu/tree.c:1972
rcu_gp_kthread+0x9a/0x370 kernel/rcu/tree.c:2145
kthread+0x42e/0x520 kernel/kthread.c:334
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
</TASK>
rcu: Stack dump where RCU GP kthread last ran:
NMI backtrace for cpu 0
CPU: 0 PID: 4384 Comm: syz.0.22 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
<IRQ>
dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
rcu_check_gp_kthread_starvation+0x1cd/0x250 kernel/rcu/tree_stall.h:487
print_other_cpu_stall+0x1110/0x1270 kernel/rcu/tree_stall.h:592
check_cpu_stall kernel/rcu/tree_stall.h:745 [inline]
rcu_pending kernel/rcu/tree.c:3936 [inline]
rcu_sched_clock_irq+0x845/0x1120 kernel/rcu/tree.c:2619
update_process_times+0x193/0x200 kernel/time/timer.c:2021
tick_sched_handle kernel/time/tick-sched.c:254 [inline]
tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
__run_hrtimer kernel/time/hrtimer.c:1685 [inline]
__hrtimer_run_queues+0x4b0/0xb60 kernel/time/hrtimer.c:1749
hrtimer_interrupt+0x397/0x8b0 kernel/time/hrtimer.c:1811
local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
__sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
sysvec_apic_timer_interrupt+0x9b/0xc0 arch/x86/kernel/apic/apic.c:1108
</IRQ>
<TASK>
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:check_preemption_disabled+0x37/0x110 lib/smp_processor_id.c:55
Code: 04 25 28 00 00 00 48 89 44 24 08 65 8b 05 a9 ee 42 76 65 8b 0d 12 49 43 76 f7 c1 ff ff ff 7f 74 1f 65 48 8b 0c 25 28 00 00 00 <48> 3b 4c 24 08 0f 85 c4 00 00 00 48 83 c4 10 5b 41 5e 41 5f 5d c3
RSP: 0018:ffffc9000347f840 EFLAGS: 00000202
RAX: 0000000000000000 RBX: 0000000000000000 RCX: a9d0bbd076518200
RDX: 0000000000000000 RSI: ffffffff8a7a2a20 RDI: ffffffff8a7a29e0
RBP: ffffc9000347f930 R08: dffffc0000000000 R09: 1ffffffff203d218
R10: dffffc0000000000 R11: fffffbfff203d219 R12: dffffc0000000000
R13: 1ffff9200068ff2c R14: 1ffff9200068ff14 R15: dffffc0000000000
rcu_lockdep_current_cpu_online+0x35/0x130 kernel/rcu/tree.c:1171
rcu_read_lock_held_common kernel/rcu/update.c:112 [inline]
rcu_read_lock_sched_held+0x71/0x110 kernel/rcu/update.c:123
task_css include/linux/cgroup.h:496 [inline]
mem_cgroup_from_task+0x49/0x110 mm/memcontrol.c:935
count_memcg_event_mm+0x164/0x370 include/linux/memcontrol.h:1080
handle_mm_fault+0x134/0x4440 mm/memory.c:4863
faultin_page mm/gup.c:976 [inline]
__get_user_pages+0x952/0x11e0 mm/gup.c:1197
populate_vma_page_range+0x213/0x290 mm/gup.c:1529
__mm_populate+0x275/0x3b0 mm/gup.c:1638
do_mlock+0x49c/0x550 mm/mlock.c:688
__do_sys_mlock mm/mlock.c:696 [inline]
__se_sys_mlock mm/mlock.c:694 [inline]
__x64_sys_mlock+0x5c/0x70 mm/mlock.c:694
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f96dbd85e59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeea3e9b88 EFLAGS: 00000246 ORIG_RAX: 0000000000000095
RAX: ffffffffffffffda RBX: 00007f96dc00dfa0 RCX: 00007f96dbd85e59
RDX: 0000000000000000 RSI: 0000000000800000 RDI: 0000200000000000
RBP: 00007f96dbe1be6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f96dc00dfac R14: 00007f96dc00dfa0 R15: 00007f96dc00dfa0
</TASK>


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