WARNING in __folio_set_anon

Status: upstream: reported C repro on 2026/09/24 05:00
Subsystems: mm ext4
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+c181d3198e98f8aef8b9@syzkaller.appspotmail.com
Fix commit: drivers/char/mem: mmap readonly MAP_SHARED-/dev/zero correctly
Patched on: [ci-upstream-linux-next-kasan-gce-root ci-upstream-rust-kasan-gce], missing on: [ci-qemu-gce-upstream-auto ci-qemu-native-arm64-kvm ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-net-kasan-gce ci-upstream-net-this-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb]
First crash: 8d04h, last: 8d02h
▶ ▼ ✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision
5d3e0a10 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ WARNING in __folio_set_anon 2026/09/24 02:40 2026/09/24 02:40 2026/09/24 03:01 0a1606bc
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH] drivers/char/mem: mmap readonly MAP_SHARED-/dev/zero correctly 12 (12) 2026/09/29 06:14
[syzbot] [mm?] [ext4?] WARNING in __folio_set_anon 5 (6) 2026/09/24 09:27

Sample crash report:
------------[ cut here ]------------
WARNING: ./include/linux/pagemap.h:1130 at vma_flags_is_cow_mapping include/linux/mm.h:2315 [inline], CPU#1: syz.0.17/4884
WARNING: ./include/linux/pagemap.h:1130 at vma_is_cow_mapping include/linux/mm.h:2329 [inline], CPU#1: syz.0.17/4884
WARNING: ./include/linux/pagemap.h:1130 at linear_anon_page_index include/linux/pagemap.h:1130 [inline], CPU#1: syz.0.17/4884
WARNING: ./include/linux/pagemap.h:1130 at __folio_set_anon+0x240/0x298 mm/rmap.c:1491, CPU#1: syz.0.17/4884
Modules linked in:
CPU: 1 UID: 0 PID: 4884 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/14/2026
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : linear_anon_page_index include/linux/mm.h:2315 [inline]
pc : __folio_set_anon+0x240/0x298 mm/rmap.c:1491
lr : vma_flags_is_cow_mapping include/linux/mm.h:2315 [inline]
lr : vma_is_cow_mapping include/linux/mm.h:2329 [inline]
lr : linear_anon_page_index include/linux/pagemap.h:1130 [inline]
lr : __folio_set_anon+0x240/0x298 mm/rmap.c:1491
sp : ffff800095456de0
x29: ffff800095456df0 x28: 0000000000020000 x27: 1fffe00019e1007c
x26: ffff0000cf0803e0 x25: 0000000000020000 x24: dfff800000000000
x23: 0000000020000000 x22: 0000000000000000 x21: 00000000200020d1
x20: ffff0000cf0803c0 x19: fffffdffc3c10000 x18: 00000000ffffffff
x17: 0000000000000003 x16: ffff800088b97000 x15: ffff80008a849000
x14: 000000000062064d x13: 0000000000000001 x12: 0000000000000000
x11: 0000000000000000 x10: 000000000000003d x9 : 0000000000000000
x8 : 0000000000000000 x7 : ffff800080c16020 x6 : 0000000000000000
x5 : 0000000000000000 x4 : 0000000000000001 x3 : ffff800080ab2d0c
x2 : 0000000000000000 x1 : ffff0000d07a1d80 x0 : 0000000000000000
Call trace:
 vma_flags_is_cow_mapping include/linux/mm.h:2315 [inline] (P)
 vma_is_cow_mapping include/linux/mm.h:2329 [inline] (P)
 linear_anon_page_index include/linux/pagemap.h:1130 [inline] (P)
 __folio_set_anon+0x240/0x298 mm/rmap.c:1491 (P)
 folio_add_new_anon_rmap+0x1a8/0x10ac mm/rmap.c:1663
 map_anon_folio_pmd_nopf+0xfc/0x160 mm/huge_memory.c:1365
 collapse_huge_page mm/khugepaged.c:1438 [inline]
 mthp_collapse mm/khugepaged.c:1532 [inline]
 collapse_scan_pmd mm/khugepaged.c:1781 [inline]
 collapse_single_pmd+0x21e0/0x3748 mm/khugepaged.c:2797
 madvise_collapse+0x2a4/0x6f4 mm/khugepaged.c:3231
 madvise_vma_behavior+0x3e8/0x339c mm/madvise.c:1372
 madvise_walk_vmas+0x4c8/0x9bc mm/madvise.c:1721
 madvise_do_behavior+0x5f0/0x7c0 mm/madvise.c:1916
 do_madvise+0x28c/0x2f0 mm/madvise.c:2014
 __do_sys_madvise mm/madvise.c:2023 [inline]
 __se_sys_madvise mm/madvise.c:2021 [inline]
 __arm64_sys_madvise+0xac/0xc8 mm/madvise.c:2021
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:758
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:777
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:590
irq event stamp: 1412
hardirqs last  enabled at (1411): [<ffff8000869b7264>] __raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:210 [inline]
hardirqs last  enabled at (1411): [<ffff8000869b7264>] _raw_spin_unlock_irqrestore+0x38/0x98 kernel/locking/spinlock.c:221
hardirqs last disabled at (1412): [<ffff800086991a8c>] el1_brk64+0x20/0x54 arch/arm64/kernel/entry-common.c:445
softirqs last  enabled at (1120): [<ffff80008013c050>] local_bh_enable include/linux/bottom_half.h:33 [inline]
softirqs last  enabled at (1120): [<ffff80008013c050>] put_cpu_fpsimd_context arch/arm64/kernel/fpsimd.c:251 [inline]
softirqs last  enabled at (1120): [<ffff80008013c050>] fpsimd_restore_current_state+0x39c/0x9c8 arch/arm64/kernel/fpsimd.c:1797
softirqs last disabled at (1118): [<ffff80008013bcf8>] local_bh_disable include/linux/bottom_half.h:20 [inline]
softirqs last disabled at (1118): [<ffff80008013bcf8>] get_cpu_fpsimd_context arch/arm64/kernel/fpsimd.c:234 [inline]
softirqs last disabled at (1118): [<ffff80008013bcf8>] fpsimd_restore_current_state+0x44/0x9c8 arch/arm64/kernel/fpsimd.c:1790
---[ end trace 0000000000000000 ]---

Crashes (4):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/23 12:36 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 38872197cae2 abce1216 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-gce-arm64 WARNING in __folio_set_anon
2026/09/23 11:57 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 38872197cae2 abce1216 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-gce-arm64 WARNING in __folio_set_anon
2026/09/23 11:17 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 38872197cae2 abce1216 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci-upstream-gce-arm64 WARNING in __folio_set_anon
2026/09/23 10:37 git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci 38872197cae2 abce1216 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-gce-arm64 WARNING in __folio_set_anon
* Struck through repros no longer work on HEAD.