mm: page_alloc: move mlocked flag clearance into free_pages_prepare()

In the Linux kernel, the following vulnerability has been resolved:

mm: page_alloc: move mlocked flag clearance into free_pages_prepare()

Syzbot reported a bad page state problem caused by a page being freed
using free_page() still having a mlocked flag at free_pages_prepare()
stage:

BUG: Bad page state in process syz.5.504 pfn:61f45
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x61f45
flags: 0xfff00000080204(referenced|workingset|mlocked|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000080204 0000000000000000 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x400dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO), pid 8443, tgid 8442 (syz.5.504), ts 201884660643, free_ts 201499827394
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1537
prep_new_page mm/page_alloc.c:1545 [inline]
get_page_from_freelist+0x303f/0x3190 mm/page_alloc.c:3457
__alloc_pages_noprof+0x292/0x710 mm/page_alloc.c:4733
alloc_pages_mpol_noprof+0x3e8/0x680 mm/mempolicy.c:2265
kvm_coalesced_mmio_init+0x1f/0xf0 virt/kvm/coalesced_mmio.c:99
kvm_create_vm virt/kvm/kvm_main.c:1235 [inline]
kvm_dev_ioctl_create_vm virt/kvm/kvm_main.c:5488 [inline]
kvm_dev_ioctl+0x12dc/0x2240 virt/kvm/kvm_main.c:5530
__do_compat_sys_ioctl fs/ioctl.c:1007 [inline]
__se_compat_sys_ioctl+0x510/0xc90 fs/ioctl.c:950
do_syscall_32_irqs_on arch/x86/entry/common.c:165 [inline]
__do_fast_syscall_32+0xb4/0x110 arch/x86/entry/common.c:386
do_fast_syscall_32+0x34/0x80 arch/x86/entry/common.c:411
entry_SYSENTER_compat_after_hwframe+0x84/0x8e
page last free pid 8399 tgid 8399 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1108 [inline]
free_unref_folios+0xf12/0x18d0 mm/page_alloc.c:2686
folios_put_refs+0x76c/0x860 mm/swap.c:1007
free_pages_and_swap_cache+0x5c8/0x690 mm/swap_state.c:335
__tlb_batch_free_encoded_pages mm/mmu_gather.c:136 [inline]
tlb_batch_pages_flush mm/mmu_gather.c:149 [inline]
tlb_flush_mmu_free mm/mmu_gather.c:366 [inline]
tlb_flush_mmu+0x3a3/0x680 mm/mmu_gather.c:373
tlb_finish_mmu+0xd4/0x200 mm/mmu_gather.c:465
exit_mmap+0x496/0xc40 mm/mmap.c:1926
__mmput+0x115/0x390 kernel/fork.c:1348
exit_mm+0x220/0x310 kernel/exit.c:571
do_exit+0x9b2/0x28e0 kernel/exit.c:926
do_group_exit+0x207/0x2c0 kernel/exit.c:1088
__do_sys_exit_group kernel/exit.c:1099 [inline]
__se_sys_exit_group kernel/exit.c:1097 [inline]
__x64_sys_exit_group+0x3f/0x40 kernel/exit.c:1097
x64_sys_call+0x2634/0x2640 arch/x86/include/generated/asm/syscalls_64.h:232
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Modules linked in:
CPU: 0 UID: 0 PID: 8442 Comm: syz.5.504 Not tainted 6.12.0-rc6-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
bad_page+0x176/0x1d0 mm/page_alloc.c:501
free_page_is_bad mm/page_alloc.c:918 [inline]
free_pages_prepare mm/page_alloc.c:1100 [inline]
free_unref_page+0xed0/0xf20 mm/page_alloc.c:2638
kvm_destroy_vm virt/kvm/kvm_main.c:1327 [inline]
kvm_put_kvm+0xc75/0x1350 virt/kvm/kvm_main.c:1386
kvm_vcpu_release+0x54/0x60 virt/kvm/kvm_main.c:4143
__fput+0x23f/0x880 fs/file_table.c:431
task_work_run+0x24f/0x310 kernel/task_work.c:239
exit_task_work include/linux/task_work.h:43 [inline]
do_exit+0xa2f/0x28e0 kernel/exit.c:939
do_group_exit+0x207/0x2c0 kernel/exit.c:1088
__do_sys_exit_group kernel/exit.c:1099 [in
---truncated---