WARNING in folio_large_mapcount

Status: fixed on 2025/07/08 00:33
Subsystems: mm
[Documentation on labels]
Reported-by: syzbot+2b99589e33edbe9475ca@syzkaller.appspotmail.com
Fix commit: 595cf683519a mm/khugepaged: fix race with folio split/free using temporary reference
First crash: 438d, last: 418d
▶ ▼ Discussions (5)
Title Replies (including bot) Last reply
Re: [akpm-mm:mm-unstable 36/67] mm/khugepaged.c:2337:7: error: implicit declaration of function 'folio_expected_ref_count'; did you mean 'folio_ref_count'? 1 (1) 2025/05/29 03:46
[PATCH V3 1/2] mm/khugepaged: fix race with folio split/free using temporary reference 7 (7) 2025/05/27 08:57
[PATCH V2 2/2] mm/khugepaged: fix race with folio split/free using temporary reference 2 (2) 2025/05/24 21:48
[PATCH] mm/khugepaged: Fix race with folio splitting in hpage_collapse_scan_file() 8 (8) 2025/05/23 07:50
[syzbot] [mm?] WARNING in folio_large_mapcount 5 (7) 2025/05/22 07:11

Sample crash report:
 madvise_vma_behavior mm/madvise.c:1333 [inline]
 madvise_walk_vmas mm/madvise.c:1539 [inline]
 madvise_do_behavior+0xd66/0x3750 mm/madvise.c:1731
 do_madvise+0x174/0x220 mm/madvise.c:1824
 __do_sys_madvise mm/madvise.c:1833 [inline]
 __se_sys_madvise mm/madvise.c:1831 [inline]
 __x64_sys_madvise+0xa7/0xc0 mm/madvise.c:1831
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
------------[ cut here ]------------
WARNING: CPU: 0 PID: 38 at ./include/linux/mm.h:1111 folio_large_mapcount+0xd0/0x110 include/linux/mm.h:1111
Modules linked in:
CPU: 0 UID: 0 PID: 38 Comm: khugepaged Not tainted 6.15.0-syzkaller-10820-gcd2e103d57e5 #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:folio_large_mapcount+0xd0/0x110 include/linux/mm.h:1111
Code: 04 38 84 c0 75 29 8b 03 ff c0 5b 41 5e 41 5f e9 81 01 e6 fe cc e8 50 fb 95 ff 48 89 df 48 c7 c6 40 17 98 8b e8 71 9e dd ff 90 <0f> 0b 90 eb b6 89 d9 80 e1 07 80 c1 03 38 c1 7c cb 48 89 df e8 b7
RSP: 0018:ffffc90000ae7740 EFLAGS: 00010246
RAX: 74c8365846fc7a00 RBX: ffffea000136c000 RCX: 74c8365846fc7a00
RDX: 0000000000000001 RSI: ffffffff8db5d737 RDI: ffff888140aada00
RBP: ffffc90000ae7ab0 R08: ffffc90000ae70e7 R09: 1ffff9200015ce1c
R10: dffffc0000000000 R11: fffff5200015ce1d R12: 1ffffd400026d800
R13: dffffc0000000000 R14: 0000000000000000 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888125c5f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe0423e2f98 CR3: 000000002ee5e000 CR4: 0000000000350ef0
Call Trace:
 <TASK>
 folio_mapcount include/linux/mm.h:1145 [inline]
 is_refcount_suitable+0x350/0x430 mm/khugepaged.c:553
 hpage_collapse_scan_file+0x6cf/0x4340 mm/khugepaged.c:2321
 khugepaged_scan_mm_slot mm/khugepaged.c:2437 [inline]
 khugepaged_do_scan mm/khugepaged.c:2538 [inline]
 khugepaged+0xa2a/0x1690 mm/khugepaged.c:2594
 kthread+0x711/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/02 09:04 upstream cd2e103d57e5 3d2f584d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-root WARNING in folio_large_mapcount
2025/05/13 08:18 upstream 627277ba7c23 f6671af7 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING in folio_large_mapcount
* Struck through repros no longer work on HEAD.