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charset="UTF-8" Hello, syzbot found the following issue on: HEAD commit: 88cbd8ac379c Add linux-next specific files for 20251120 git tree: linux-next console output: https://syzkaller.appspot.com/x/log.txt?x=114d9a12580000 kernel config: https://syzkaller.appspot.com/x/.config?x=270004e181b25d45 dashboard link: https://syzkaller.appspot.com/bug?extid=5b19bad23ac7f44bf8b8 compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=147e7a12580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11b3d658580000 Downloadable assets: disk image: https://storage.googleapis.com/syzbot-assets/7d546d2103e3/disk-88cbd8ac.raw.xz vmlinux: https://storage.googleapis.com/syzbot-assets/af9601889c35/vmlinux-88cbd8ac.xz kernel image: https://storage.googleapis.com/syzbot-assets/7747417abb8f/bzImage-88cbd8ac.xz The issue was bisected to: commit c52a4e7b13eaa55a2c4bb08488b2cf9bd188ea85 Author: Matthew Wilcox (Oracle) Date: Mon Nov 10 20:32:02 2025 +0000 mm: use vma_start_write_killable() in dup_mmap() bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=13e9da12580000 final oops: https://syzkaller.appspot.com/x/report.txt?x=1019da12580000 console output: https://syzkaller.appspot.com/x/log.txt?x=17e9da12580000 IMPORTANT: if you fix the issue, please add the following tag to the commit: Reported-by: syzbot+5b19bad23ac7f44bf8b8@syzkaller.appspotmail.com Fixes: c52a4e7b13ea ("mm: use vma_start_write_killable() in dup_mmap()") ------------[ cut here ]------------ refcount_t: saturated; leaking memory. WARNING: lib/refcount.c:19 at refcount_warn_saturate+0x13a/0x1d0 lib/refcount.c:19, CPU#1: syz.0.48/6130 Modules linked in: CPU: 1 UID: 0 PID: 6130 Comm: syz.0.48 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025 RIP: 0010:refcount_warn_saturate+0x13a/0x1d0 lib/refcount.c:19 Code: e0 cd be 8b e8 17 da f3 fc 90 0f 0b 90 90 eb b7 e8 fb be 31 fd c6 05 39 0d d8 0a 01 90 48 c7 c7 20 cd be 8b e8 f7 d9 f3 fc 90 <0f> 0b 90 90 eb 97 e8 db be 31 fd c6 05 1d 0d d8 0a 01 90 48 c7 c7 RSP: 0018:ffffc9000411f568 EFLAGS: 00010246 RAX: df83eb6d8e87c500 RBX: 0000000000000000 RCX: ffff8880790bbd00 RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002 RBP: ffffc9000411f690 R08: ffff8880b87247d3 R09: 1ffff110170e48fa R10: dffffc0000000000 R11: ffffed10170e48fb R12: ffff888025562a80 R13: 1ffff92000823ec0 R14: ffff888025562a80 R15: 0000000000000000 FS: 00007fdb5cf9a6c0(0000) GS:ffff888125fb9000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fdb5cf99f98 CR3: 00000000289ea000 CR4: 00000000003526f0 Call Trace: __refcount_add_not_zero include/linux/refcount.h:187 [inline] refcount_add_not_zero include/linux/refcount.h:212 [inline] __vma_enter_locked+0x593/0x5d0 mm/mmap_lock.c:67 __vma_start_write+0x23/0x140 mm/mmap_lock.c:99 vma_start_write include/linux/mmap_lock.h:213 [inline] vma_merge_existing_range mm/vma.c:900 [inline] vma_modify+0xf62/0x1a70 mm/vma.c:1611 vma_modify_flags_uffd+0x204/0x250 mm/vma.c:1704 userfaultfd_clear_vma mm/userfaultfd.c:1997 [inline] userfaultfd_release_all+0x34c/0x5d0 mm/userfaultfd.c:2116 userfaultfd_release+0xe7/0x1b0 fs/userfaultfd.c:887 __fput+0x44c/0xa70 fs/file_table.c:468 task_work_run+0x1d4/0x260 kernel/task_work.c:233 get_signal+0x11ec/0x1340 kernel/signal.c:2807 arch_do_signal_or_restart+0x9a/0x7a0 arch/x86/kernel/signal.c:337 __exit_to_user_mode_loop kernel/entry/common.c:41 [inline] exit_to_user_mode_loop+0x87/0x4f0 kernel/entry/common.c:75 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:226 [inline] syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:256 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:159 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:194 [inline] do_syscall_64+0x2e9/0xfa0 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fdb5c18f749 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fdb5cf9a038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 RAX: fffffffffffffffc RBX: 00007fdb5c3e5fa0 RCX: 00007fdb5c18f749 RDX: 0000200000000100 RSI: 00000000c028aa05 RDI: 0000000000000003 RBP: 00007fdb5c213f91 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fdb5c3e6038 R14: 00007fdb5c3e5fa0 R15: 00007fff2e39e5c8 --- This report is generated by a bot. It may contain errors. See https://goo.gl/tpsmEJ for more information about syzbot. syzbot engineers can be reached at syzkaller@googlegroups.com. syzbot will keep track of this issue. See: https://goo.gl/tpsmEJ#status for how to communicate with syzbot. For information about bisection process see: https://goo.gl/tpsmEJ#bisection If the report is already addressed, let syzbot know by replying with: #syz fix: exact-commit-title If you want syzbot to run the reproducer, reply with: #syz test: git://repo/address.git branch-or-commit-hash If you attach or paste a git patch, syzbot will apply it before testing. If you want to overwrite report's subsystems, reply with: #syz set subsystems: new-subsystem (See the list of subsystem names on the web dashboard) If the report is a duplicate of another one, reply with: #syz dup: exact-subject-of-another-report If you want to undo deduplication, reply with: #syz undup