[syzbot] [mm?] KMSAN: uninit-value in swap_writeout

[syzbot <syzbot+178fff6149127421c2cc@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    ea1013c15392 Merge tag 'bpf-fixes' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11d2e31a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b3903bdf68407a14
dashboard link: https://syzkaller.appspot.com/bug?extid=178fff6149127421c2cc
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: i386

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/27172fba4316/disk-ea1013c1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ac8c65aa1d08/vmlinux-ea1013c1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/42241f684d1d/bzImage-ea1013c1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+178fff6149127421c2cc@syzkaller.appspotmail.com

=====================================================
BUG: KMSAN: uninit-value in is_folio_zero_filled mm/page_io.c:188 [inline]
BUG: KMSAN: uninit-value in swap_writeout+0x468/0x1390 mm/page_io.c:263
 is_folio_zero_filled mm/page_io.c:188 [inline]
 swap_writeout+0x468/0x1390 mm/page_io.c:263
 shmem_writeout+0x1abb/0x1f60 mm/shmem.c:1662
 writeout mm/vmscan.c:649 [inline]
 pageout mm/vmscan.c:698 [inline]
 shrink_folio_list+0x5920/0x7fc0 mm/vmscan.c:1418
 evict_folios+0x999d/0xbf30 mm/vmscan.c:4711
 try_to_shrink_lruvec+0x12b6/0x17e0 mm/vmscan.c:4874
 lru_gen_shrink_lruvec mm/vmscan.c:5023 [inline]
 shrink_lruvec+0x46f/0x4f10 mm/vmscan.c:5784
 shrink_node_memcgs mm/vmscan.c:6020 [inline]
 shrink_node+0xf1e/0x51e0 mm/vmscan.c:6061
 shrink_zones mm/vmscan.c:6300 [inline]
 do_try_to_free_pages+0x849/0x26b0 mm/vmscan.c:6362
 try_to_free_mem_cgroup_pages+0x3ae/0x950 mm/vmscan.c:6690
 try_charge_memcg+0x80f/0x1c50 mm/memcontrol.c:2388
 obj_cgroup_charge_pages+0x2ed/0x600 mm/memcontrol.c:2823
 __memcg_kmem_charge_page+0x14a/0x4c0 mm/memcontrol.c:2867
 __alloc_frozen_pages_noprof+0x3ba/0xab0 mm/page_alloc.c:5227
 alloc_pages_mpol+0x328/0x860 mm/mempolicy.c:2486
 alloc_frozen_pages_noprof mm/mempolicy.c:2557 [inline]
 alloc_pages_noprof+0x102/0x280 mm/mempolicy.c:2577
 io_mem_alloc_compound io_uring/memmap.c:30 [inline]
 io_region_allocate_pages+0x164/0x900 io_uring/memmap.c:165
 io_create_region+0x6d0/0x830 io_uring/memmap.c:220
 io_allocate_scq_urings+0x1e3/0x8a0 io_uring/io_uring.c:3379
 io_uring_create+0x7b5/0x1040 io_uring/io_uring.c:3643
 io_uring_setup io_uring/io_uring.c:3718 [inline]
 __do_sys_io_uring_setup io_uring/io_uring.c:3752 [inline]
 __se_sys_io_uring_setup+0x3f0/0x410 io_uring/io_uring.c:3743
 __ia32_sys_io_uring_setup+0x76/0xb0 io_uring/io_uring.c:3743
 ia32_sys_call+0x2c57/0x4340 arch/x86/include/generated/asm/syscalls_32.h:426
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x15a/0x330 arch/x86/entry/syscall_32.c:307
 do_fast_syscall_32+0x38/0x80 arch/x86/entry/syscall_32.c:332
 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:370
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e

Uninit was created at:
 __alloc_frozen_pages_noprof+0x421/0xab0 mm/page_alloc.c:5233
 alloc_pages_mpol+0x328/0x860 mm/mempolicy.c:2486
 folio_alloc_mpol_noprof+0x56/0x1d0 mm/mempolicy.c:2505
 shmem_alloc_folio mm/shmem.c:1890 [inline]
 shmem_alloc_and_add_folio+0xc56/0x1bd0 mm/shmem.c:1932
 shmem_get_folio_gfp+0xad3/0x1fc0 mm/shmem.c:2556
 shmem_get_folio mm/shmem.c:2662 [inline]
 shmem_symlink+0x562/0xad0 mm/shmem.c:4129
 vfs_symlink+0x42f/0x4c0 fs/namei.c:5514
 do_symlinkat+0x2ae/0xbb0 fs/namei.c:5541
 __do_sys_symlinkat fs/namei.c:5562 [inline]
 __se_sys_symlinkat fs/namei.c:5559 [inline]
 __ia32_sys_symlinkat+0xf5/0x180 fs/namei.c:5559
 ia32_sys_call+0x385e/0x4340 arch/x86/include/generated/asm/syscalls_32.h:305
 do_syscall_32_irqs_on arch/x86/entry/syscall_32.c:83 [inline]
 __do_fast_syscall_32+0x15a/0x330 arch/x86/entry/syscall_32.c:307
 do_fast_syscall_32+0x38/0x80 arch/x86/entry/syscall_32.c:332
 do_SYSENTER_32+0x1f/0x30 arch/x86/entry/syscall_32.c:370
 entry_SYSENTER_compat_after_hwframe+0x84/0x8e

CPU: 0 UID: 0 PID: 7862 Comm: syz.2.517 Tainted: G             L      syzkaller #0 PREEMPT(none) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
=====================================================


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