Re: [syzbot] [mm?] INFO: rcu detected stall in vm_mmap_pgoff

[syzbot <syzbot+890a1df7294175947697@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    ec039126b7fa Add linux-next specific files for 20260611
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1616a3b6580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d0d1fa2afcbce17c
dashboard link: https://syzkaller.appspot.com/bug?extid=890a1df7294175947697
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=161e44ae580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/be809c32a471/disk-ec039126.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/13ea1053e3b5/vmlinux-ec039126.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1bcdab47ddc8/bzImage-ec039126.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+890a1df7294175947697@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
rcu: 	Tasks blocked on level-0 rcu_node (CPUs 0-1): P6292/2:b..l
rcu: 	(detected by 1, t=10502 jiffies, g=19045, q=7088 ncpus=2)
task:syz.0.104       state:R  running task     stack:23736 pid:6292  tgid:6290  ppid:5799   task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5504 [inline]
 __schedule+0x172b/0x5550 kernel/sched/core.c:7228
 preempt_schedule_irq+0x4d/0xa0 kernel/sched/core.c:7552
 irqentry_exit_to_kernel_mode include/linux/irq-entry-common.h:539 [inline]
 irqentry_exit+0x14f/0x8c0 kernel/entry/common.c:167
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:674
RIP: 0010:get_current arch/x86/include/asm/current.h:25 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:245 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp8+0x8/0xa0 kernel/kcov.c:321
Code: 74 0a 18 48 89 44 0a 20 c3 cc cc cc cc cc 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 48 8b 04 24 <65> 48 8b 0d f8 7e f5 10 65 44 8b 05 18 7f f5 10 41 81 e0 00 00 ff
RSP: 0018:ffffc90004217640 EFLAGS: 00000206
RAX: ffffffff8238c5c3 RBX: 0000000000000000 RCX: ffff888029bb9f00
RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000005
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffff94000269461 R12: 0000000000000000
R13: 000000004d28c027 R14: 0000000000000005 R15: 0000000000000001
 pte_user_accessible_page arch/x86/include/asm/pgtable.h:1689 [inline]
 __page_table_check_ptes_set+0x263/0x320 mm/page_table_check.c:211
 page_table_check_ptes_set include/linux/page_table_check.h:83 [inline]
 set_ptes include/linux/pgtable.h:447 [inline]
 set_pte_range+0x83e/0x890 mm/memory.c:5588
 finish_fault+0xd12/0xfc0 mm/memory.c:5724
 do_read_fault mm/memory.c:5864 [inline]
 do_fault mm/memory.c:5994 [inline]
 do_pte_missing+0x17c4/0x2940 mm/memory.c:4566
 handle_pte_fault mm/memory.c:6379 [inline]
 __handle_mm_fault mm/memory.c:6517 [inline]
 handle_mm_fault+0xdc2/0x14d0 mm/memory.c:6686
 faultin_page mm/gup.c:1126 [inline]
 __get_user_pages+0x16d4/0x2620 mm/gup.c:1428
 populate_vma_page_range+0x2be/0x3c0 mm/gup.c:1860
 __mm_populate+0x25f/0x390 mm/gup.c:1963
 mm_populate include/linux/mm.h:4171 [inline]
 vm_mmap_pgoff+0x3ad/0x4f0 mm/util.c:586
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1ce857ce59
RSP: 002b:00007f1ce7bde028 EFLAGS: 00000246 ORIG_RAX: 0000000000000009
RAX: ffffffffffffffda RBX: 00007f1ce87f5fa0 RCX: 00007f1ce857ce59
RDX: b635773f04ebbeef RSI: 0000000000b36000 RDI: 0000200000000000
RBP: 00007f1ce8612d6f R08: ffffffffffffffff R09: 0000000000000000
R10: 0000000000008031 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1ce87f6038 R14: 00007f1ce87f5fa0 R15: 00007ffe40d7f778
 </TASK>
rcu: rcu_preempt kthread timer wakeup didn't happen for 8806 jiffies! g19045 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402
rcu: 	Possible timer handling issue on cpu=0 timer-softirq=8166
rcu: rcu_preempt kthread starved for 8807 jiffies! g19045 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x402 ->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:I stack:27576 pid:18    tgid:18    ppid:2      task_flags:0x208040 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5504 [inline]
 __schedule+0x172b/0x5550 kernel/sched/core.c:7228
 __schedule_loop kernel/sched/core.c:7307 [inline]
 schedule+0x164/0x360 kernel/sched/core.c:7322
 schedule_timeout+0x158/0x2c0 kernel/time/sleep_timeout.c:99
 rcu_gp_fqs_loop+0x312/0x11b0 kernel/rcu/tree.c:2123
 rcu_gp_kthread+0x9e/0x2b0 kernel/rcu/tree.c:2325
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:64
Code: 6b 84 02 e9 13 cc 03 00 cc cc cc 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 66 90 0f 00 2d 93 81 2b 00 fb f4 <c3> cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc cc 90 90 90 90 90
RSP: 0018:ffffffff8e007de0 EFLAGS: 00000246
RAX: 00000000000f42dd RBX: ffffffff8199fabc RCX: 0000000080000001
RDX: 0000000000000001 RSI: ffffffff8d978313 RDI: ffffffff8bcc4d80
RBP: ffffffff8e007eb0 R08: ffff8880b8633d5b R09: 1ffff110170c67ab
R10: dffffc0000000000 R11: ffffed10170c67ac R12: 0000000000000000
R13: 1ffffffff1c1fde8 R14: 1ffffffff1c00fc4 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888125a6b000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007faf351135c0 CR3: 000000003893c000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 arch_safe_halt arch/x86/kernel/process.c:766 [inline]
 default_idle+0x9/0x20 arch/x86/kernel/process.c:767
 default_idle_call+0x72/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:199 [inline]
 do_idle+0x1cc/0x540 kernel/sched/idle.c:355
 cpu_startup_entry+0x43/0x60 kernel/sched/idle.c:454
 rest_init+0x2de/0x300 init/main.c:717
 start_kernel+0x392/0x3e0 init/main.c:1175
 x86_64_start_reservations+0x24/0x30 arch/x86/kernel/head64.c:310
 x86_64_start_kernel+0x143/0x1c0 arch/x86/kernel/head64.c:291
 common_startup_64+0x13e/0x157
 </TASK>


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