[syzbot] [kernel?] WARNING in __mmdrop (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 05f7e89ab973 Linux 6.19
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1153465a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=df890e720d1bb80
dashboard link: https://syzkaller.appspot.com/bug?extid=237b5b985b78c1da9600
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=105297fa580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=120c12e6580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ea9f39c5175d/disk-05f7e89a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/734edeebfa32/vmlinux-05f7e89a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a2cb36d849f0/bzImage-05f7e89a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+237b5b...@syzkaller.appspotmail.com

------------[ cut here ]------------
mm == current->mm
WARNING: kernel/fork.c:720 at __mmdrop+0x5de/0x750 kernel/fork.c:720, CPU#0: syz.0.19/6013
Modules linked in:
CPU: 0 UID: 0 PID: 6013 Comm: syz.0.19 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/24/2026
RIP: 0010:__mmdrop+0x5de/0x750 kernel/fork.c:720
Code: 00 90 0f 0b e8 93 ef 41 00 90 0f 0b 90 e9 e9 fa ff ff e8 85 ef 41 00 48 89 df e8 dd 44 a9 00 e9 c0 fb ff ff e8 73 ef 41 00 90 <0f> 0b 90 e9 85 fa ff ff e8 65 ef 41 00 90 0f 0b 90 e9 5f fb ff ff
RSP: 0018:ffffc90003baf8f8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff88807aa93d40 RCX: ffffffff81d3fa45
RDX: ffff888078f73d00 RSI: ffffffff81c45eed RDI: ffff888078f74298
RBP: ffffc90003baf990 R08: 0000000000000001 R09: ffffed100f5527a8
R10: ffff88807aa93d43 R11: 0000000000000000 R12: ffff888078f73d00
R13: ffff888032e75b80 R14: ffff888032e75b80 R15: ffff8880b843bbf0
FS: 00007f9eec7116c0(0000) GS:ffff8881245e2000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2fa63fff CR3: 000000007623e000 CR4: 00000000003526f0
Call Trace:
<TASK>
mmdrop include/linux/sched/mm.h:55 [inline]
mmdrop_sched include/linux/sched/mm.h:83 [inline]
mmdrop_lazy_tlb_sched include/linux/sched/mm.h:110 [inline]
finish_task_switch.isra.0+0x76e/0xb70 kernel/sched/core.c:5143
context_switch kernel/sched/core.c:5263 [inline]
__schedule+0xfee/0x5fa0 kernel/sched/core.c:6867
preempt_schedule_common+0x42/0xc0 kernel/sched/core.c:7051
preempt_schedule_thunk+0x16/0x30 arch/x86/entry/thunk.S:12
class_preempt_destructor include/linux/preempt.h:468 [inline]
try_to_wake_up+0x644/0x1a60 kernel/sched/core.c:4070
wake_up_process kernel/sched/core.c:4349 [inline]
wake_up_q+0xa1/0x130 kernel/sched/core.c:1087
futex_wake+0x460/0x530 kernel/futex/waitwake.c:198
do_futex+0x32b/0x350 kernel/futex/syscalls.c:135
__do_sys_futex kernel/futex/syscalls.c:207 [inline]
__se_sys_futex kernel/futex/syscalls.c:188 [inline]
__x64_sys_futex+0x34f/0x4d0 kernel/futex/syscalls.c:188
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9eeb79af79
Code: Unable to access opcode bytes at 0x7f9eeb79af4f.
RSP: 002b:00007f9eec7110e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007f9eeba15fa8 RCX: 00007f9eeb79af79
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007f9eeba15fac
RBP: 00007f9eeba15fa0 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffffffffffff R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9eeba16038 R14: 00007ffc9832d5e0 R15: 00007ffc9832d6c8
</TASK>


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