[syzbot] [fs?] [mm?] WARNING: bad unlock balance in hugetlb_vmdelete_list

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 846bd2225ec3 Add linux-next specific files for 20250919
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13263534580000
kernel config: https://syzkaller.appspot.com/x/.config?x=135377594f35b576
dashboard link: https://syzkaller.appspot.com/bug?extid=62edf7e27b2e8f754525
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=14a118e2580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17e204e2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c53d48022f8a/disk-846bd222.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/483534e784c8/vmlinux-846bd222.xz
kernel image: https://storage.googleapis.com/syzbot-assets/721b36eec9b3/bzImage-846bd222.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+62edf7...@syzkaller.appspotmail.com

=====================================
WARNING: bad unlock balance detected!
syzkaller #0 Not tainted
-------------------------------------
syz.0.8060/30977 is trying to release lock (&vma_lock->rw_sema) at:
[<ffffffff82903959>] hugetlb_vmdelete_list+0x179/0x1c0 fs/hugetlbfs/inode.c:501
but there are no more locks to release!

other info that might help us debug this:
3 locks held by syz.0.8060/30977:
#0: ffff88807d8da420 (sb_writers#12){.+.+}-{0:0}, at: mnt_want_write+0x41/0x90 fs/namespace.c:508
#1: ffff888034404648 (&sb->s_type->i_mutex_key#20){+.+.}-{4:4}, at: inode_lock_killable include/linux/fs.h:985 [inline]
#1: ffff888034404648 (&sb->s_type->i_mutex_key#20){+.+.}-{4:4}, at: do_truncate+0x171/0x220 fs/open.c:63
#2: ffff888034404918 (&hugetlbfs_i_mmap_rwsem_key){+.+.}-{4:4}, at: i_mmap_lock_write include/linux/fs.h:548 [inline]
#2: ffff888034404918 (&hugetlbfs_i_mmap_rwsem_key){+.+.}-{4:4}, at: hugetlb_vmtruncate fs/hugetlbfs/inode.c:639 [inline]
#2: ffff888034404918 (&hugetlbfs_i_mmap_rwsem_key){+.+.}-{4:4}, at: hugetlbfs_setattr+0x489/0x6d0 fs/hugetlbfs/inode.c:879

stack backtrace:
CPU: 1 UID: 0 PID: 30977 Comm: syz.0.8060 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_unlock_imbalance_bug+0xdc/0xf0 kernel/locking/lockdep.c:5298
__lock_release kernel/locking/lockdep.c:5537 [inline]
lock_release+0x269/0x3e0 kernel/locking/lockdep.c:5889
up_write+0x2d/0x420 kernel/locking/rwsem.c:1642
hugetlb_vmdelete_list+0x179/0x1c0 fs/hugetlbfs/inode.c:501
hugetlb_vmtruncate fs/hugetlbfs/inode.c:641 [inline]
hugetlbfs_setattr+0x4d1/0x6d0 fs/hugetlbfs/inode.c:879
notify_change+0xc1a/0xf40 fs/attr.c:546
do_truncate+0x1a4/0x220 fs/open.c:68
handle_truncate fs/namei.c:3516 [inline]
do_open fs/namei.c:3899 [inline]
path_openat+0x306c/0x3830 fs/namei.c:4054
do_filp_open+0x1fa/0x410 fs/namei.c:4081
do_sys_openat2+0x121/0x1c0 fs/open.c:1435
do_sys_open fs/open.c:1450 [inline]
__do_sys_open fs/open.c:1458 [inline]
__se_sys_open fs/open.c:1454 [inline]
__x64_sys_open+0x11e/0x150 fs/open.c:1454
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdea5b8eec9
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:00007fdea6945038 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007fdea5de5fa0 RCX: 00007fdea5b8eec9
RDX: 0000000000000100 RSI: 000000000014927e RDI: 0000200000000340
RBP: 00007fdea5c11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdea5de6038 R14: 00007fdea5de5fa0 R15: 00007ffe42e704f8
</TASK>
------------[ cut here ]------------
DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)): count = 0x0, magic = 0xffff8880295a5408, owner = 0x1, curr 0xffff8880260d9e40, list empty
WARNING: kernel/locking/rwsem.c:1381 at __up_write kernel/locking/rwsem.c:1380 [inline], CPU#1: syz.0.8060/30977
WARNING: kernel/locking/rwsem.c:1381 at up_write+0x3a2/0x420 kernel/locking/rwsem.c:1643, CPU#1: syz.0.8060/30977
Modules linked in:
CPU: 1 UID: 0 PID: 30977 Comm: syz.0.8060 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:__up_write kernel/locking/rwsem.c:1380 [inline]
RIP: 0010:up_write+0x3a2/0x420 kernel/locking/rwsem.c:1643
Code: d0 48 c7 c7 00 f0 aa 8b 48 c7 c6 20 f2 aa 8b 48 8b 14 24 4c 89 f1 4d 89 e0 4c 8b 4c 24 08 41 52 e8 b3 39 e6 ff 48 83 c4 08 90 <0f> 0b 90 90 e9 6d fd ff ff 48 c7 c1 74 0b e5 8f 80 e1 07 80 c1 03
RSP: 0018:ffffc900051076c8 EFLAGS: 00010282
RAX: b37f99c54516e500 RBX: ffff8880295a5408 RCX: ffff8880260d9e40
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: dffffc0000000000 R08: ffffc900051073e7 R09: 1ffff92000a20e7c
R10: dffffc0000000000 R11: fffff52000a20e7d R12: 0000000000000001
R13: ffff8880295a5460 R14: ffff8880295a5408 R15: 1ffff110052b4a82
FS: 00007fdea69456c0(0000) GS:ffff8881258a2000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fdea51fed58 CR3: 00000000779ba000 CR4: 00000000003526f0
Call Trace:
<TASK>
hugetlb_vmdelete_list+0x179/0x1c0 fs/hugetlbfs/inode.c:501
hugetlb_vmtruncate fs/hugetlbfs/inode.c:641 [inline]
hugetlbfs_setattr+0x4d1/0x6d0 fs/hugetlbfs/inode.c:879
notify_change+0xc1a/0xf40 fs/attr.c:546
do_truncate+0x1a4/0x220 fs/open.c:68
handle_truncate fs/namei.c:3516 [inline]
do_open fs/namei.c:3899 [inline]
path_openat+0x306c/0x3830 fs/namei.c:4054
do_filp_open+0x1fa/0x410 fs/namei.c:4081
do_sys_openat2+0x121/0x1c0 fs/open.c:1435
do_sys_open fs/open.c:1450 [inline]
__do_sys_open fs/open.c:1458 [inline]
__se_sys_open fs/open.c:1454 [inline]
__x64_sys_open+0x11e/0x150 fs/open.c:1454
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fdea5b8eec9
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:00007fdea6945038 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007fdea5de5fa0 RCX: 00007fdea5b8eec9
RDX: 0000000000000100 RSI: 000000000014927e RDI: 0000200000000340
RBP: 00007fdea5c11f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fdea5de6038 R14: 00007fdea5de5fa0 R15: 00007ffe42e704f8
</TASK>


---
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[syzbot]

For archival purposes, forwarding an incoming command email to
linux-...@vger.kernel.org, syzkall...@googlegroups.com.

***

Subject: [PATCH] Fix a lock imbalance bug in hugetlb_vmdelete_list() that
Author: karti...@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master

Fix a lock imbalance bug in hugetlb_vmdelete_list() that causes:

WARNING: bad unlock balance detected!

hugetlb_vmdelete_list+0x179/0x1c0 is trying to release lock
(&vma_lock->rw_sema) but there are no more locks to release!

The issue is a race condition between multiple threads operating on the
same VMA:

1. Thread 1 calls hugetlb_vma_trylock_write() when vma->vm_private_data=NULL
2. trylock returns success (no lock needed for this VMA type)
3. Thread 2 allocates a lock structure: vma->vm_private_data=&new_lock
4. Thread 1 calls hugetlb_vma_unlock_write(), sees non-NULL vm_private_data
5. Thread 1 tries to unlock a lock it never acquired → crash

The fix is to save the VMA lock state at the time we make the locking
decision, rather than checking it again at unlock time. This prevents
the time-of-check-time-of-use (TOCTOU) race condition.

Reported-by: syzbot+62edf7...@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=62edf7e27b2e8f754525
Fixes: 8d9bfb2608cf ("hugetlb: add vma based lock for pmd sharing")
Signed-off-by: Deepanshu Kartikey <karti...@gmail.com>
---
fs/hugetlbfs/inode.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 9e0625167517..ae3e07eacd37 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -475,15 +475,16 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
zap_flags_t zap_flags)
{
struct vm_area_struct *vma;
-
/*
* end == 0 indicates that the entire range after start should be
* unmapped. Note, end is exclusive, whereas the interval tree takes
* an inclusive "last".
*/
vma_interval_tree_foreach(vma, root, start, end ? end - 1 : ULONG_MAX) {
+ struct hugetlb_vma_lock *vma_lock;
unsigned long v_start;
unsigned long v_end;
+ vma_lock = vma->vm_private_data;

if (!hugetlb_vma_trylock_write(vma))
continue;
@@ -498,7 +499,8 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
* vmas. Therefore, lock is not held when calling
* unmap_hugepage_range for private vmas.
*/
- hugetlb_vma_unlock_write(vma);
+ if (vma_lock)
+ hugetlb_vma_unlock_write(vma);
}
}

--
2.43.0

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in hugetlb_vma_assert_locked

------------[ cut here ]------------
WARNING: mm/hugetlb.c:368 at hugetlb_vma_assert_locked+0x1dd/0x250 mm/hugetlb.c:368, CPU#1: syz.0.28/6594
Modules linked in:
CPU: 1 UID: 0 PID: 6594 Comm: syz.0.28 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025

RIP: 0010:hugetlb_vma_assert_locked+0x1dd/0x250 mm/hugetlb.c:368
Code: 2e e8 97 6e a1 ff eb 0c e8 90 6e a1 ff eb 05 e8 89 6e a1 ff 5b 41 5c 41 5d 41 5e 41 5f 5d e9 da 41 6a 09 cc e8 74 6e a1 ff 90 <0f> 0b 90 eb e5 e8 69 6e a1 ff 90 0f 0b 90 eb da 48 c7 c1 70 7c e4
RSP: 0018:ffffc90003637368 EFLAGS: 00010293
RAX: ffffffff821f22cc RBX: 0000000000000000 RCX: ffff888030330000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000001 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520006c6e70 R12: ffff888026856500
R13: 1ffff1100bd744fc R14: dffffc0000000000 R15: 0000000000000080
FS: 00007fb2310906c0(0000) GS:ffff8881258c5000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007fb23108ff98 CR3: 0000000075cce000 CR4: 00000000003526f0
Call Trace:
<TASK>
huge_pmd_unshare+0x2c8/0x540 mm/hugetlb.c:7622
__unmap_hugepage_range+0x6e3/0x1aa0 mm/hugetlb.c:5901
unmap_hugepage_range+0x32e/0x410 mm/hugetlb.c:6089
hugetlb_vmdelete_list+0x189/0x1f0 fs/hugetlbfs/inode.c:495
hugetlb_vmtruncate fs/hugetlbfs/inode.c:643 [inline]
hugetlbfs_setattr+0x4d1/0x6d0 fs/hugetlbfs/inode.c:881

notify_change+0xc1a/0xf40 fs/attr.c:546
do_truncate+0x1a4/0x220 fs/open.c:68
handle_truncate fs/namei.c:3516 [inline]
do_open fs/namei.c:3899 [inline]
path_openat+0x306c/0x3830 fs/namei.c:4054
do_filp_open+0x1fa/0x410 fs/namei.c:4081

do_sys_openat2+0x121/0x1c0 fs/open.c:1437
do_sys_open fs/open.c:1452 [inline]
__do_sys_open fs/open.c:1460 [inline]
__se_sys_open fs/open.c:1456 [inline]
__x64_sys_open+0x11e/0x150 fs/open.c:1456

do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7fb23018eec9

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:00007fb231090038 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00007fb2303e5fa0 RCX: 00007fb23018eec9

RDX: 0000000000000100 RSI: 000000000014927e RDI: 0000200000000340

RBP: 00007fb230211f91 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007fb2303e6038 R14: 00007fb2303e5fa0 R15: 00007fff95fa5748
</TASK>


Tested on:

commit: ce7f1a98 Add linux-next specific files for 20250923
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=129a4d34580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1be6fa3d47bce66e

dashboard link: https://syzkaller.appspot.com/bug?extid=62edf7e27b2e8f754525
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=17b2cce2580000