linux-kernel - Re: [syzbot] [mm?] WARNING: lock held when returning to user space in lock_next

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Message-ID: <687067ef.a00a0220.26a83e.002b.GAE@google.com>
Date: Thu, 10 Jul 2025 18:25:03 -0700
From: syzbot <syzbot+80011ad33eec39e6ce42@...kaller.appspotmail.com>
To: hdanton@...a.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [mm?] WARNING: lock held when returning to user space in lock_next_vma

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING: bad unlock balance in query_matching_vma

=====================================
WARNING: bad unlock balance detected!
6.16.0-rc5-next-20250710-syzkaller-08625-gb551c4e2a98a-dirty #0 Not tainted
-------------------------------------
syz.0.40/6692 is trying to release lock (vm_lock) at:
[<ffffffff825976c4>] get_next_vma fs/proc/task_mmu.c:181 [inline]
[<ffffffff825976c4>] query_vma_find_by_addr fs/proc/task_mmu.c:513 [inline]
[<ffffffff825976c4>] query_matching_vma+0x344/0x600 fs/proc/task_mmu.c:545
but there are no more locks to release!

other info that might help us debug this:
1 lock held by syz.0.40/6692:
 #0: ffffffff8e13c4e0 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:331 [inline]
 #0: ffffffff8e13c4e0 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:841 [inline]
 #0: ffffffff8e13c4e0 (rcu_read_lock){....}-{1:3}, at: query_vma_find_by_addr fs/proc/task_mmu.c:511 [inline]
 #0: ffffffff8e13c4e0 (rcu_read_lock){....}-{1:3}, at: query_matching_vma+0x152/0x600 fs/proc/task_mmu.c:545

stack backtrace:
CPU: 1 UID: 0 PID: 6692 Comm: syz.0.40 Not tainted 6.16.0-rc5-next-20250710-syzkaller-08625-gb551c4e2a98a-dirty #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_unlock_imbalance_bug+0xdc/0xf0 kernel/locking/lockdep.c:5301
 __lock_release kernel/locking/lockdep.c:5540 [inline]
 lock_release+0x269/0x3e0 kernel/locking/lockdep.c:5892
 vma_refcount_put include/linux/mmap_lock.h:141 [inline]
 vma_end_read include/linux/mmap_lock.h:237 [inline]
 unlock_vma+0x70/0x180 fs/proc/task_mmu.c:135
 get_next_vma fs/proc/task_mmu.c:181 [inline]
 query_vma_find_by_addr fs/proc/task_mmu.c:513 [inline]
 query_matching_vma+0x344/0x600 fs/proc/task_mmu.c:545
 do_procmap_query fs/proc/task_mmu.c:631 [inline]
 procfs_procmap_ioctl+0x3f9/0xd50 fs/proc/task_mmu.c:749
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:598 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:584
 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
RIP: 0033:0x7f2c38b8e929
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:00007f2c399b2038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f2c38db6080 RCX: 00007f2c38b8e929
RDX: 0000200000000180 RSI: 00000000c0686611 RDI: 0000000000000003
RBP: 00007f2c38c10b39 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000001 R14: 00007f2c38db6080 R15: 00007fff905431d8
 </TASK>
------------[ cut here ]------------
WARNING: ./include/linux/mmap_lock.h:292 at vma_assert_attached include/linux/mmap_lock.h:292 [inline], CPU#0: syz.0.40/6692
WARNING: ./include/linux/mmap_lock.h:292 at vma_mark_detached+0x1fa/0x2d0 mm/mmap_lock.c:109, CPU#0: syz.0.40/6692
Modules linked in:
CPU: 0 UID: 0 PID: 6692 Comm: syz.0.40 Not tainted 6.16.0-rc5-next-20250710-syzkaller-08625-gb551c4e2a98a-dirty #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
RIP: 0010:vma_assert_attached include/linux/mmap_lock.h:292 [inline]
RIP: 0010:vma_mark_detached+0x1fa/0x2d0 mm/mmap_lock.c:109
Code: 48 8b 05 09 f2 9a 10 48 3b 44 24 08 0f 85 d0 00 00 00 48 83 c4 10 5b 41 5c 41 5e 41 5f 5d c3 cc cc cc cc cc e8 27 a8 b5 ff 90 <0f> 0b 90 e9 45 ff ff ff e8 19 a8 b5 ff 90 0f 0b 90 e9 92 fe ff ff
RSP: 0018:ffffc90003b6f7c0 EFLAGS: 00010293
RAX: ffffffff820a0e39 RBX: ffff88807904b280 RCX: ffff888033a68000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000000 R08: ffff88807904b303 R09: 1ffff1100f209660
R10: dffffc0000000000 R11: ffffed100f209661 R12: dffffc0000000000
R13: 0000000000000000 R14: ffff88807904b300 R15: ffff888049f08c20
FS:  0000000000000000(0000) GS:ffff888125bd0000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f93657ae7d0 CR3: 000000000df36000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 exit_mmap+0x537/0xb50 mm/mmap.c:1307
 __mmput+0x118/0x420 kernel/fork.c:1120
 exit_mm+0x1da/0x2c0 kernel/exit.c:581
 do_exit+0x648/0x2300 kernel/exit.c:947
 do_group_exit+0x21c/0x2d0 kernel/exit.c:1100
 get_signal+0x1286/0x1340 kernel/signal.c:3034
 arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:208 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f2c38b8e929
Code: Unable to access opcode bytes at 0x7f2c38b8e8ff.
RSP: 002b:00007f2c399b20e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: fffffffffffffe00 RBX: 00007f2c38db6088 RCX: 00007f2c38b8e929
RDX: 0000000000000000 RSI: 0000000000000080 RDI: 00007f2c38db6088
RBP: 00007f2c38db6080 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f2c38db608c
R13: 0000000000000000 R14: 00007fff905430f0 R15: 00007fff905431d8
 </TASK>


Tested on:

commit:         b551c4e2 Add linux-next specific files for 20250710
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16fa20f0580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=90b2e63e925474ab
dashboard link: https://syzkaller.appspot.com/bug?extid=80011ad33eec39e6ce42
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
patch:          https://syzkaller.appspot.com/x/patch.diff?x=127d3a8c580000