[syzbot] [fs?] WARNING: bad unlock balance in namespace_unlock

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: ce7f1a983b07 Add linux-next specific files for 20250923
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=151b8d34580000
kernel config: https://syzkaller.appspot.com/x/.config?x=91ae0b9529ab8226
dashboard link: https://syzkaller.appspot.com/bug?extid=0d671007a95cd2835e05
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=131b8d34580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16a194e2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/3f1b65edb63f/disk-ce7f1a98.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b132cb8d99cd/vmlinux-ce7f1a98.xz
kernel image: https://storage.googleapis.com/syzbot-assets/80f316094043/bzImage-ce7f1a98.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0d6710...@syzkaller.appspotmail.com

=====================================
WARNING: bad unlock balance detected!
syzkaller #0 Not tainted
-------------------------------------
syz.3.25/6203 is trying to release lock (namespace_sem) at:
[<ffffffff82401096>] namespace_unlock+0x486/0x760 fs/namespace.c:1705
but there are no more locks to release!

other info that might help us debug this:
no locks held by syz.3.25/6203.

stack backtrace:
CPU: 0 UID: 0 PID: 6203 Comm: syz.3.25 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:5527 [inline]
lock_release+0x212/0x3e0 kernel/locking/lockdep.c:5889
up_write+0x2d/0x420 kernel/locking/rwsem.c:1642
namespace_unlock+0x486/0x760 fs/namespace.c:1705
class_namespace_excl_destructor fs/namespace.c:96 [inline]
copy_mnt_ns+0x6e5/0x880 fs/namespace.c:4176
create_new_namespaces+0xd1/0x720 kernel/nsproxy.c:78
unshare_nsproxy_namespaces+0x11c/0x170 kernel/nsproxy.c:218
ksys_unshare+0x4c8/0x8c0 kernel/fork.c:3198
__do_sys_unshare kernel/fork.c:3269 [inline]
__se_sys_unshare kernel/fork.c:3267 [inline]
__x64_sys_unshare+0x38/0x50 kernel/fork.c:3267
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: 0033:0x7f7cd618eec9
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:00007f7cd6feb038 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00007f7cd63e6180 RCX: 00007f7cd618eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000040020000
RBP: 00007f7cd6211f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7cd63e6218 R14: 00007f7cd63e6180 R15: 00007ffc3db53b78
</TASK>
------------[ cut here ]------------
DEBUG_RWSEMS_WARN_ON((rwsem_owner(sem) != current) && !rwsem_test_oflags(sem, RWSEM_NONSPINNABLE)): count = 0x3, magic = 0xffffffff8e48df00, owner = 0xffff88803389dac0, curr 0xffff88803408dac0, list not empty
WARNING: kernel/locking/rwsem.c:1381 at __up_write kernel/locking/rwsem.c:1380 [inline], CPU#0: syz.3.25/6203
WARNING: kernel/locking/rwsem.c:1381 at up_write+0x3a2/0x420 kernel/locking/rwsem.c:1643, CPU#0: syz.3.25/6203
Modules linked in:
CPU: 0 UID: 0 PID: 6203 Comm: syz.3.25 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 80 ff aa 8b 48 c7 c6 a0 01 ab 8b 48 8b 14 24 4c 89 f1 4d 89 e0 4c 8b 4c 24 08 41 52 e8 83 37 e6 ff 48 83 c4 08 90 <0f> 0b 90 90 e9 6d fd ff ff 48 c7 c1 74 37 c3 8f 80 e1 07 80 c1 03
RSP: 0018:ffffc90003d2faf0 EFLAGS: 00010296
RAX: 4aab14382228fb00 RBX: ffffffff8e48df00 RCX: ffff88803408dac0
RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002
RBP: dffffc0000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1c3a654 R12: ffff88803389dac0
R13: ffffffff8e48df58 R14: ffffffff8e48df00 R15: 1ffffffff1c91be1
FS: 00007f7cd6feb6c0(0000) GS:ffff888125a0a000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b33163fff CR3: 0000000027b4e000 CR4: 00000000003526f0
Call Trace:
<TASK>
namespace_unlock+0x486/0x760 fs/namespace.c:1705
class_namespace_excl_destructor fs/namespace.c:96 [inline]
copy_mnt_ns+0x6e5/0x880 fs/namespace.c:4176
create_new_namespaces+0xd1/0x720 kernel/nsproxy.c:78
unshare_nsproxy_namespaces+0x11c/0x170 kernel/nsproxy.c:218
ksys_unshare+0x4c8/0x8c0 kernel/fork.c:3198
__do_sys_unshare kernel/fork.c:3269 [inline]
__se_sys_unshare kernel/fork.c:3267 [inline]
__x64_sys_unshare+0x38/0x50 kernel/fork.c:3267
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: 0033:0x7f7cd618eec9
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:00007f7cd6feb038 EFLAGS: 00000246 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 00007f7cd63e6180 RCX: 00007f7cd618eec9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000040020000
RBP: 00007f7cd6211f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7cd63e6218 R14: 00007f7cd63e6180 R15: 00007ffc3db53b78
</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 syzk...@googlegroups.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

[Edward Adam Davis]

#syz test

diff --git a/fs/namespace.c b/fs/namespace.c
index ac1aedafe05e..c22febeda1ac 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -4134,7 +4134,6 @@ struct mnt_namespace *copy_mnt_ns(u64 flags, struct mnt_namespace *ns,
new = copy_tree(old, old->mnt.mnt_root, copy_flags);
if (IS_ERR(new)) {
emptied_ns = new_ns;
- namespace_unlock();
return ERR_CAST(new);
}
if (user_ns != ns->user_ns) {

[syzbot]

Hello,

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

=====================================
WARNING: bad unlock balance detected!
syzkaller #0 Not tainted
-------------------------------------

syz.2.1222/11521 is trying to release lock (&sighand->siglock) at:
[<ffffffff818337dd>] spin_unlock include/linux/spinlock.h:391 [inline]
[<ffffffff818337dd>] copy_process+0x27bd/0x3c20 kernel/fork.c:2486

but there are no more locks to release!

other info that might help us debug this:

1 lock held by syz.2.1222/11521:
#0: ffffffff8e374a90 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x2154/0x3c20 kernel/fork.c:2328

stack backtrace:
CPU: 1 UID: 0 PID: 11521 Comm: syz.2.1222 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
__raw_spin_unlock include/linux/spinlock_api_smp.h:141 [inline]
_raw_spin_unlock+0x16/0x50 kernel/locking/spinlock.c:186
spin_unlock include/linux/spinlock.h:391 [inline]
copy_process+0x27bd/0x3c20 kernel/fork.c:2486
kernel_clone+0x21e/0x840 kernel/fork.c:2657
__do_sys_clone3 kernel/fork.c:2980 [inline]
__se_sys_clone3+0x292/0x300 kernel/fork.c:2959

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: 0033:0x7f4df65c3609
Code: d7 08 00 48 8d 3d 9c d7 08 00 e8 e2 28 f6 ff 66 90 b8 ea ff ff ff 48 85 ff 74 2c 48 85 d2 74 27 49 89 c8 b8 b3 01 00 00 0f 05 <48> 85 c0 7c 18 74 01 c3 31 ed 48 83 e4 f0 4c 89 c7 ff d2 48 89 c7
RSP: 002b:00007ffef05e2ba8 EFLAGS: 00000206 ORIG_RAX: 00000000000001b3
RAX: ffffffffffffffda RBX: 00007f4df65459f0 RCX: 00007f4df65c3609
RDX: 00007f4df65459f0 RSI: 0000000000000058 RDI: 00007ffef05e2bf0
RBP: 00007f4df73456c0 R08: 00007f4df73456c0 R09: 00007ffef05e2cd7
R10: 0000000000000008 R11: 0000000000000206 R12: ffffffffffffffa8
R13: 000000000000000b R14: 00007ffef05e2bf0 R15: 00007ffef05e2cd8

</TASK>
------------[ cut here ]------------

pvqspinlock: lock 0xffff8880280b8000 has corrupted value 0x0!
WARNING: kernel/locking/qspinlock_paravirt.h:506 at __pv_queued_spin_unlock_slowpath+0x1fe/0x2a0 kernel/locking/qspinlock_paravirt.h:504, CPU#0: syz.2.1222/11521
Modules linked in:
CPU: 0 UID: 0 PID: 11521 Comm: syz.2.1222 Not tainted syzkaller #0 PREEMPT(full)

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

RIP: 0010:__pv_queued_spin_unlock_slowpath+0x1fe/0x2a0 kernel/locking/qspinlock_paravirt.h:504
Code: 88 f8 a4 f6 48 89 d8 48 c1 e8 03 42 0f b6 04 28 84 c0 0f 85 93 00 00 00 8b 13 48 c7 c7 e0 1c ab 8b 48 89 de e8 83 56 03 f6 90 <0f> 0b 90 90 eb 95 48 c7 c7 10 f5 20 8e 4c 89 f6 4c 89 fa e8 da c9
RSP: 0018:ffffc900040df8e0 EFLAGS: 00010246
RAX: b9dfea7c18b7cb00 RBX: ffff8880280b8000 RCX: ffff88802f4bbc80

RDX: 0000000000000000 RSI: 0000000000000001 RDI: 0000000000000002

RBP: 1ffff11005017001 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffffbfff1c3a654 R12: dffffc0000000000
R13: dffffc0000000000 R14: ffff8880280b8010 R15: ffff8880280b8008
FS: 0000555588b1a500(0000) GS:ffff888125a0a000(0000) knlGS:0000000000000000

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

CR2: 00007f41bcd45f98 CR3: 00000000667c6000 CR4: 00000000003526f0
Call Trace:
<TASK>
__raw_callee_save___pv_queued_spin_unlock_slowpath+0x15/0x30
.slowpath+0x9/0x18
pv_queued_spin_unlock arch/x86/include/asm/paravirt.h:562 [inline]
queued_spin_unlock arch/x86/include/asm/qspinlock.h:57 [inline]
do_raw_spin_unlock+0x122/0x240 kernel/locking/spinlock_debug.c:142
__raw_spin_unlock include/linux/spinlock_api_smp.h:142 [inline]
_raw_spin_unlock+0x1e/0x50 kernel/locking/spinlock.c:186
spin_unlock include/linux/spinlock.h:391 [inline]
copy_process+0x27bd/0x3c20 kernel/fork.c:2486
kernel_clone+0x21e/0x840 kernel/fork.c:2657
__do_sys_clone3 kernel/fork.c:2980 [inline]
__se_sys_clone3+0x292/0x300 kernel/fork.c:2959

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: 0033:0x7f4df65c3609
Code: d7 08 00 48 8d 3d 9c d7 08 00 e8 e2 28 f6 ff 66 90 b8 ea ff ff ff 48 85 ff 74 2c 48 85 d2 74 27 49 89 c8 b8 b3 01 00 00 0f 05 <48> 85 c0 7c 18 74 01 c3 31 ed 48 83 e4 f0 4c 89 c7 ff d2 48 89 c7
RSP: 002b:00007ffef05e2ba8 EFLAGS: 00000206 ORIG_RAX: 00000000000001b3
RAX: ffffffffffffffda RBX: 00007f4df65459f0 RCX: 00007f4df65c3609
RDX: 00007f4df65459f0 RSI: 0000000000000058 RDI: 00007ffef05e2bf0
RBP: 00007f4df73456c0 R08: 00007f4df73456c0 R09: 00007ffef05e2cd7
R10: 0000000000000008 R11: 0000000000000206 R12: ffffffffffffffa8
R13: 000000000000000b R14: 00007ffef05e2bf0 R15: 00007ffef05e2cd8
</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=13f04f12580000

kernel config: https://syzkaller.appspot.com/x/.config?x=91ae0b9529ab8226
dashboard link: https://syzkaller.appspot.com/bug?extid=0d671007a95cd2835e05
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=12932142580000

[Edward Adam Davis]

This code segment is already protected by guards, namespace_unlock()
should not appear here.

Reported-by: syzbot+0d6710...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=0d671007a95cd2835e05
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
fs/namespace.c | 1 -
1 file changed, 1 deletion(-)

--
2.43.0

[Edward Adam Davis]

#syz test

diff --git a/fs/namespace.c b/fs/namespace.c
index ac1aedafe05e..c22febeda1ac 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -4134,7 +4134,6 @@ struct mnt_namespace *copy_mnt_ns(u64 flags, struct mnt_namespace *ns,
new = copy_tree(old, old->mnt.mnt_root, copy_flags);
if (IS_ERR(new)) {
emptied_ns = new_ns;
- namespace_unlock();
return ERR_CAST(new);
}
if (user_ns != ns->user_ns) {

diff --git a/kernel/fork.c b/kernel/fork.c
index e9a7fb5c3e49..a0b8eeeb1d27 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2349,7 +2349,7 @@ __latent_entropy struct task_struct *copy_process(
if (need_futex_hash_allocate_default(clone_flags)) {
retval = futex_hash_allocate_default();
if (retval)
- goto bad_fork_core_free;
+ goto bad_fork_cancel_cgroup;
/*
* If we fail beyond this point we don't free the allocated
* futex hash map. We assume that another thread will be created

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+0d6710...@syzkaller.appspotmail.com
Tested-by: syzbot+0d6710...@syzkaller.appspotmail.com

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=14d0a142580000

kernel config: https://syzkaller.appspot.com/x/.config?x=91ae0b9529ab8226
dashboard link: https://syzkaller.appspot.com/bug?extid=0d671007a95cd2835e05
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=174f2142580000

Note: testing is done by a robot and is best-effort only.

[Jan Kara]

On Wed 24-09-25 18:29:04, Edward Adam Davis wrote:
> This code segment is already protected by guards, namespace_unlock()
> should not appear here.
>
> Reported-by: syzbot+0d6710...@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=0d671007a95cd2835e05
> Signed-off-by: Edward Adam Davis <ead...@qq.com>

Indeed. Feel free to add:

Reviewed-by: Jan Kara <ja...@suse.cz>

Honza

> ---
> fs/namespace.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/fs/namespace.c b/fs/namespace.c
> index ac1aedafe05e..c22febeda1ac 100644
> --- a/fs/namespace.c
> +++ b/fs/namespace.c
> @@ -4134,7 +4134,6 @@ struct mnt_namespace *copy_mnt_ns(u64 flags, struct mnt_namespace *ns,
> new = copy_tree(old, old->mnt.mnt_root, copy_flags);
> if (IS_ERR(new)) {
> emptied_ns = new_ns;
> - namespace_unlock();
> return ERR_CAST(new);
> }
> if (user_ns != ns->user_ns) {
> --
> 2.43.0
>

--
Jan Kara <ja...@suse.com>
SUSE Labs, CR

[Al Viro]

On Wed, Sep 24, 2025 at 02:03:56PM +0200, Jan Kara wrote:
> On Wed 24-09-25 18:29:04, Edward Adam Davis wrote:
> > This code segment is already protected by guards, namespace_unlock()
> > should not appear here.
> >
> > Reported-by: syzbot+0d6710...@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=0d671007a95cd2835e05
> > Signed-off-by: Edward Adam Davis <ead...@qq.com>
>
> Indeed. Feel free to add:
>
> Reviewed-by: Jan Kara <ja...@suse.cz>

I wonder where does that line come from, though. Mismerge somewhere?
d7b7253a0adc "copy_mnt_ns(): use guards" includes this:

@@ -4185,13 +4186,11 @@ struct mnt_namespace *copy_mnt_ns(unsigned long flags, struct mnt_namespace *ns,

new = copy_tree(old, old->mnt.mnt_root, copy_flags);
if (IS_ERR(new)) {
emptied_ns = new_ns;
- namespace_unlock();
return ERR_CAST(new);
}
if (user_ns != ns->user_ns) {

- lock_mount_hash();
+ guard(mount_writer)();
lock_mnt_tree(new);
- unlock_mount_hash();
}
new_ns->root = new;