Message-ID: <3925be8e-2aad-49c1-9a50-492749ff4329@lucifer.local>
Date: Tue, 17 Jun 2025 20:45:00 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: syzbot <syzbot+52343d77314d6c0447fe@...kaller.appspotmail.com>
Cc: Liam.Howlett@...cle.com, akpm@...ux-foundation.org, jannh@...gle.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org, pfalcato@...e.de,
        syzkaller-bugs@...glegroups.com, vbabka@...e.cz
Subject: Re: [syzbot] [mm?] WARNING: bad unlock balance in move_pgt_entry

On Tue, Jun 17, 2025 at 01:11:31AM -0700, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    050f8ad7b58d Add linux-next specific files for 20250616
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=16389e82580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=d2efc7740224b93a
> dashboard link: https://syzkaller.appspot.com/bug?extid=52343d77314d6c0447fe
> compiler:       Debian clang version 20.1.6 (++20250514063057+1e4d39e07757-1~exp1~20250514183223.118), Debian LLD 20.1.6
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11389e82580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16824370580000

Sadly non-repro locally. Seems to need some kind of very specific device setup?

But I can see what this is, a silly bug in move_pgt_entry().

The maybe_take_rmap_locks() check should be moved out of the override check...

I'll send a fix-patch on thread, while there's a lot of ongoing discussion there
this should fix the proximate issue.

Thanks!

>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/49faa18d2f53/disk-050f8ad7.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/7c6f9cd7fe5d/vmlinux-050f8ad7.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/84a08d6403ee/bzImage-050f8ad7.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+52343d77314d6c0447fe@...kaller.appspotmail.com
>
> =====================================
> WARNING: bad unlock balance detected!
> 6.16.0-rc2-next-20250616-syzkaller #0 Not tainted
> -------------------------------------
> syz-executor359/6969 is trying to release lock (&mapping->i_mmap_rwsem) at:
> [<ffffffff82104277>] i_mmap_unlock_write include/linux/fs.h:557 [inline]
> [<ffffffff82104277>] maybe_drop_rmap_locks mm/mremap.c:197 [inline]
> [<ffffffff82104277>] move_pgt_entry+0xfa7/0x1170 mm/mremap.c:686
> but there are no more locks to release!
>
> other info that might help us debug this:
> 1 lock held by syz-executor359/6969:
>  #0: ffff88802f641760 (&mm->mmap_lock){++++}-{4:4}, at: mmap_write_lock_killable include/linux/mmap_lock.h:374 [inline]
>  #0: ffff88802f641760 (&mm->mmap_lock){++++}-{4:4}, at: do_mremap mm/mremap.c:2371 [inline]
>  #0: ffff88802f641760 (&mm->mmap_lock){++++}-{4:4}, at: __do_sys_mremap mm/mremap.c:2453 [inline]
>  #0: ffff88802f641760 (&mm->mmap_lock){++++}-{4:4}, at: __se_sys_mremap+0x3c0/0xc60 mm/mremap.c:2421
>
> stack backtrace:
> CPU: 1 UID: 0 PID: 6969 Comm: syz-executor359 Not tainted 6.16.0-rc2-next-20250616-syzkaller #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
>  up_write+0x2d/0x420 kernel/locking/rwsem.c:1629
>  i_mmap_unlock_write include/linux/fs.h:557 [inline]
>  maybe_drop_rmap_locks mm/mremap.c:197 [inline]
>  move_pgt_entry+0xfa7/0x1170 mm/mremap.c:686
>  move_page_tables+0xcde/0x2940 mm/mremap.c:1367
>  copy_vma_and_data mm/mremap.c:1807 [inline]
>  move_vma+0xd5e/0x2010 mm/mremap.c:1913
>  mremap_to+0x7e7/0x8b0 mm/mremap.c:2106
>  do_mremap mm/mremap.c:2396 [inline]
>  __do_sys_mremap mm/mremap.c:2453 [inline]
>  __se_sys_mremap+0x8f5/0xc60 mm/mremap.c:2421
>  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: 0033:0x7f33da2e43b9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 1d 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f33da273168 EFLAGS: 00000246 ORIG_RAX: 0000000000000019
> RAX: ffffffffffffffda RBX: 00007f33da3673f8 RCX: 00007f33da2e43b9
> RDX: 0000000000200000 RSI: 0000000000600600 RDI: 0000200000000000
> RBP: 00007f33da3673f0 R08: 0000200000a00000 R09: 0000000000000000
> R10: 0000000000000003 R11: 0000000000000246 R12: 00007f33da3673fc
> R13: 000000000000006e R14: 00007ffccf0ef660 R15: 00007ffccf0ef748
>  </TASK>
> ------------[ cut here ]------------
> DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)): count = 0x0, magic = 0xffff888033554d00, owner = 0x0, curr 0xffff888033b15a00, list empty
> WARNING: kernel/locking/rwsem.c:1368 at __up_write kernel/locking/rwsem.c:1367 [inline], CPU#1: syz-executor359/6969
> WARNING: kernel/locking/rwsem.c:1368 at up_write+0x3a2/0x420 kernel/locking/rwsem.c:1630, CPU#1: syz-executor359/6969
> Modules linked in:
> CPU: 1 UID: 0 PID: 6969 Comm: syz-executor359 Not tainted 6.16.0-rc2-next-20250616-syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
> RIP: 0010:__up_write kernel/locking/rwsem.c:1367 [inline]
> RIP: 0010:up_write+0x3a2/0x420 kernel/locking/rwsem.c:1630
> Code: d0 48 c7 c7 60 ee 8a 8b 48 c7 c6 80 f0 8a 8b 48 8b 14 24 4c 89 f1 4d 89 e0 4c 8b 4c 24 08 41 52 e8 23 3b e6 ff 48 83 c4 08 90 <0f> 0b 90 90 e9 6d fd ff ff 48 c7 c1 34 81 a1 8f 80 e1 07 80 c1 03
> RSP: 0018:ffffc9000b2ff498 EFLAGS: 00010282
> RAX: 636aee1c3dfaec00 RBX: ffff888033554d00 RCX: ffff888033b15a00
> RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
> RBP: dffffc0000000000 R08: 0000000000000003 R09: 0000000000000004
> R10: dffffc0000000000 R11: fffffbfff1bfaa14 R12: 0000000000000000
> R13: ffff888033554d58 R14: ffff888033554d00 R15: 1ffff110066aa9a1
> FS:  00007f33da2736c0(0000) GS:ffff888125d40000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007f33da29ba90 CR3: 000000002c068000 CR4: 00000000003526f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  i_mmap_unlock_write include/linux/fs.h:557 [inline]
>  maybe_drop_rmap_locks mm/mremap.c:197 [inline]
>  move_pgt_entry+0xfa7/0x1170 mm/mremap.c:686
>  move_page_tables+0xcde/0x2940 mm/mremap.c:1367
>  copy_vma_and_data mm/mremap.c:1807 [inline]
>  move_vma+0xd5e/0x2010 mm/mremap.c:1913
>  mremap_to+0x7e7/0x8b0 mm/mremap.c:2106
>  do_mremap mm/mremap.c:2396 [inline]
>  __do_sys_mremap mm/mremap.c:2453 [inline]
>  __se_sys_mremap+0x8f5/0xc60 mm/mremap.c:2421
>  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: 0033:0x7f33da2e43b9
> Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 11 1d 00 00 90 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 b0 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f33da273168 EFLAGS: 00000246 ORIG_RAX: 0000000000000019
> RAX: ffffffffffffffda RBX: 00007f33da3673f8 RCX: 00007f33da2e43b9
> RDX: 0000000000200000 RSI: 0000000000600600 RDI: 0000200000000000
> RBP: 00007f33da3673f0 R08: 0000200000a00000 R09: 0000000000000000
> R10: 0000000000000003 R11: 0000000000000246 R12: 00007f33da3673fc
> R13: 000000000000006e R14: 00007ffccf0ef660 R15: 00007ffccf0ef748
>  </TASK>
>
>
> ---
> 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@...glegroups.com.
>
> syzbot will keep track of this issue. See:
> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>
> 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

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