WARNING: bad unlock balance in copy_process
Subsystems (4)
syzbot
syzbotHello,
syzbot found the following issue on:
HEAD commit: 785cdec46e92 Merge tag 'x86-core-2025-05-25' of git://git... git tree: upstream console output: https://syzkaller.appspot.com/x/log.txt?x=132bbdf4580000 kernel config: https://syzkaller.appspot.com/x/.config?x=628e87e3a98ec1c4 dashboard link: https://syzkaller.appspot.com/bug?extid=80cb3cc5c14fad191a10 compiler: gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
Unfortunately, I don't have any reproducer for this issue yet.
Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-785cdec4.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/259338148f62/vmlinux-785cdec4.xz
kernel image: https://storage.googleapis.com/syzbot-assets/436abe9bf6f7/bzImage-785cdec4.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
=====================================
WARNING: bad unlock balance detected! 6.15.0-syzkaller-01958-g785cdec46e92 #0 Not tainted
-------------------------------------
syz.1.441/7809 is trying to release lock (&sighand->siglock) at:
[<ffffffff817a389e>] spin_unlock include/linux/spinlock.h:391 [inline] [<ffffffff817a389e>] copy_process+0x5d6e/0x9170 kernel/fork.c:2686
but there are no more locks to release!
other info that might help us debug this:
1 lock held by syz.1.441/7809:
#0: ffffffff8e41c350 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x3de8/0x9170 kernel/fork.c:2528
stack backtrace: CPU: 0 UID: 0 PID: 7809 Comm: syz.1.441 Not tainted 6.15.0-syzkaller-01958-g785cdec46e92 #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_unlock_imbalance_bug kernel/locking/lockdep.c:5301 [inline] print_unlock_imbalance_bug+0x11b/0x130 kernel/locking/lockdep.c:5275 __lock_release kernel/locking/lockdep.c:5540 [inline] lock_release+0x242/0x2f0 kernel/locking/lockdep.c:5892 __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+0x5d6e/0x9170 kernel/fork.c:2686 kernel_clone+0xfc/0x960 kernel/fork.c:2859 __do_sys_clone3+0x212/0x290 kernel/fork.c:3163 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f6443fc31c9 Code: bf 08 00 48 8d 3d dc bf 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:00007ffeb834dbb8 EFLAGS: 00000202 ORIG_RAX: 00000000000001b3 RAX: ffffffffffffffda RBX: 00007f6443f455b0 RCX: 00007f6443fc31c9 RDX: 00007f6443f455b0 RSI: 0000000000000058 RDI: 00007ffeb834dc00 RBP: 00007f6444dee6c0 R08: 00007f6444dee6c0 R09: 00007ffeb834dce7 R10: 0000000000000008 R11: 0000000000000202 R12: ffffffffffffffa8 R13: 000000000000000b R14: 00007ffeb834dc00 R15: 00007ffeb834dce8 </TASK> ------------[ cut here ]------------ pvqspinlock: lock 0xffff8880245e8940 has corrupted value 0x0! WARNING: CPU: 0 PID: 7809 at kernel/locking/qspinlock_paravirt.h:504 __pv_queued_spin_unlock_slowpath+0x237/0x330 kernel/locking/qspinlock_paravirt.h:504 Modules linked in: CPU: 0 UID: 0 PID: 7809 Comm: syz.1.441 Not tainted 6.15.0-syzkaller-01958-g785cdec46e92 #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 RIP: 0010:__pv_queued_spin_unlock_slowpath+0x237/0x330 kernel/locking/qspinlock_paravirt.h:504 Code: 03 0f b6 14 02 4c 89 e8 83 e0 07 83 c0 03 38 d0 7c 04 84 d2 75 67 41 8b 55 00 4c 89 ee 48 c7 c7 a0 79 8d 8b e8 ba e4 02 f6 90 <0f> 0b 90 90 e9 64 ff ff ff 90 0f 0b 48 89 df 4c 89 04 24 e8 31 e6 RSP: 0018:ffffc900034478d8 EFLAGS: 00010286 RAX: 0000000000000000 RBX: ffff8880245e8940 RCX: ffffffff817a98c8 RDX: ffff8880247b0000 RSI: ffffffff817a98d5 RDI: 0000000000000001 RBP: ffff8880245e8948 R08: 0000000000000001 R09: 0000000000000000 R10: 0000000000000001 R11: 6c6e697073717670 R12: ffff8880245e8950 R13: ffff8880245e8940 R14: 00000000fffffff4 R15: ffffc90003447d60 FS: 000055557a112500(0000) GS:ffff8880d69a6000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 000000110c2dcf78 CR3: 000000003467f000 CR4: 0000000000352ef0 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+0x172/0x230 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+0x5d6e/0x9170 kernel/fork.c:2686 kernel_clone+0xfc/0x960 kernel/fork.c:2859 __do_sys_clone3+0x212/0x290 kernel/fork.c:3163 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f6443fc31c9 Code: bf 08 00 48 8d 3d dc bf 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:00007ffeb834dbb8 EFLAGS: 00000202 ORIG_RAX: 00000000000001b3 RAX: ffffffffffffffda RBX: 00007f6443f455b0 RCX: 00007f6443fc31c9 RDX: 00007f6443f455b0 RSI: 0000000000000058 RDI: 00007ffeb834dc00 RBP: 00007f6444dee6c0 R08: 00007f6444dee6c0 R09: 00007ffeb834dce7 R10: 0000000000000008 R11: 0000000000000202 R12: ffffffffffffffa8 R13: 000000000000000b R14: 00007ffeb834dc00 R15: 00007ffeb834dce8 </TASK>
---
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syzbot
syzbotsyzbot has found a reproducer for the following issue on:
syzbot has found a reproducer for the following issue on:
HEAD commit: 6edf2885ebeb Merge branch 'for-next/core' into for-kernelci git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci console output: https://syzkaller.appspot.com/x/log.txt?x=16d14c7c580000 kernel config: https://syzkaller.appspot.com/x/.config?x=b8b6789b42526d72 dashboard link: https://syzkaller.appspot.com/bug?extid=80cb3cc5c14fad191a10 compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 userspace arch: arm64 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=179d9f62580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11d14c7c580000
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c72239eb6d76/disk-6edf2885.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b67e9820b2be/vmlinux-6edf2885.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0c4ab7e562f6/Image-6edf2885.gz.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
=====================================
WARNING: bad unlock balance detected!
syzkaller #0 Not tainted
-------------------------------------
syz.1.48/6865 is trying to release lock (&sighand->siglock) at:
[<ffff8000803b8634>] spin_unlock include/linux/spinlock.h:391 [inline] [<ffff8000803b8634>] copy_process+0x22d4/0x31ec kernel/fork.c:2432
but there are no more locks to release!
other info that might help us debug this:
1 lock held by syz.1.48/6865:
#0: ffff80008fa00450 (cgroup_threadgroup_rwsem){++++}-{0:0}, at: copy_process+0x2228/0x31ec kernel/fork.c:2274
stack backtrace: CPU: 0 UID: 0 PID: 6865 Comm: syz.1.48 Not tainted syzkaller #0 PREEMPT Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025 Call trace: show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C) __dump_stack+0x30/0x40 lib/dump_stack.c:94 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120 dump_stack+0x1c/0x28 lib/dump_stack.c:129 print_unlock_imbalance_bug+0xf4/0xfc kernel/locking/lockdep.c:5298 __lock_release kernel/locking/lockdep.c:-1 [inline] lock_release+0x244/0x39c kernel/locking/lockdep.c:5889 __raw_spin_unlock include/linux/spinlock_api_smp.h:141 [inline] _raw_spin_unlock+0x24/0x78 kernel/locking/spinlock.c:186 spin_unlock include/linux/spinlock.h:391 [inline] copy_process+0x22d4/0x31ec kernel/fork.c:2432 kernel_clone+0x1d8/0x84c kernel/fork.c:2605 __do_sys_clone kernel/fork.c:2748 [inline] __se_sys_clone kernel/fork.c:2716 [inline] __arm64_sys_clone+0x144/0x1a0 kernel/fork.c:2716 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:744 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:763 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596
---
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.
Quoted 20 lines · syzbot
syzbot has found a reproducer for the following issue on:
HEAD commit: 6edf2885ebeb Merge branch 'for-next/core' into for-kernelci git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci console output: https://syzkaller.appspot.com/x/log.txt?x=16d14c7c580000 kernel config: https://syzkaller.appspot.com/x/.config?x=b8b6789b42526d72 dashboard link: https://syzkaller.appspot.com/bug?extid=80cb3cc5c14fad191a10 compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8 userspace arch: arm64 syz repro: https://syzkaller.appspot.com/x/repro.syz?x=179d9f62580000 C reproducer: https://syzkaller.appspot.com/x/repro.c?x=11d14c7c580000Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c72239eb6d76/disk-6edf2885.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/b67e9820b2be/vmlinux-6edf2885.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0c4ab7e562f6/Image-6edf2885.gz.xzIMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by [email protected]
Quoted 7 lines
=====================================
WARNING: bad unlock balance detected!
syzkaller #0 Not tainted
-------------------------------------
syz.1.48/6865 is trying to release lock (&sighand->siglock) at:[<ffff8000803b8634>] spin_unlock include/linux/spinlock.h:391 [inline] [<ffff8000803b8634>] copy_process+0x22d4/0x31ec kernel/fork.c:2432
bad_fork_core_free:
sched_core_free(p);
spin_unlock(¤t->sighand->siglock); <- hereSebastian, I think it's your 7c4f75a21f63 ("futex: Allow automatic allocation of process wide futex hash") adding a "goto bad_fork_core_free;" from a place that doesn't yet have current->sighand->siglock locked?
Quoted 38 lines
but there are no more locks to release!
other info that might help us debug this:
1 lock held by syz.1.48/6865:
#0:ffff80008fa00450(cgroup_threadgroup_rwsem){++++}-{0:0}, at:copy_process+0x2228/0x31eckernel/fork.c:2274stack backtrace: CPU: 0 UID: 0 PID: 6865 Comm: syz.1.48 Not tainted syzkaller #0 PREEMPT Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025 Call trace: show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C) __dump_stack+0x30/0x40 lib/dump_stack.c:94 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120 dump_stack+0x1c/0x28 lib/dump_stack.c:129 print_unlock_imbalance_bug+0xf4/0xfc kernel/locking/lockdep.c:5298 __lock_release kernel/locking/lockdep.c:-1 [inline] lock_release+0x244/0x39c kernel/locking/lockdep.c:5889 __raw_spin_unlock include/linux/spinlock_api_smp.h:141 [inline] _raw_spin_unlock+0x24/0x78 kernel/locking/spinlock.c:186 spin_unlock include/linux/spinlock.h:391 [inline] copy_process+0x22d4/0x31ec kernel/fork.c:2432 kernel_clone+0x1d8/0x84c kernel/fork.c:2605 __do_sys_clone kernel/fork.c:2748 [inline] __se_sys_clone kernel/fork.c:2716 [inline] __arm64_sys_clone+0x144/0x1a0 kernel/fork.c:2716 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline] invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151 el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:744 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:763 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596---
If you want syzbot to run the reproducer, reply with:
#syz test:git://repo/address.gitbranch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.
Quoted 11 lines · Vlastimil Babka
Quoted 10 lines
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by [email protected]=====================================
WARNING: bad unlock balance detected!
syzkaller #0 Not tainted
-------------------------------------
syz.1.48/6865 is trying to release lock (&sighand->siglock) at:[<ffff8000803b8634>] spin_unlock include/linux/spinlock.h:391 [inline] [<ffff8000803b8634>] copy_process+0x22d4/0x31ec kernel/fork.c:2432
Quoted 7 lines
bad_fork_core_free:sched_core_free(p); spin_unlock(¤t->sighand->siglock); <- hereSebastian, I think it's your
7c4f75a21f63("futex: Allow automatic allocation of process wide futex hash") adding a "gotobad_fork_core_free;" from a place that doesn't yet havecurrent->sighand->siglocklocked?
Yes. Judging from -rc6, if futex_hash_allocate_default() fails we hold neither siglock nor tasklist_lock. sched_core_free() looks also bad as the cookie was allocated later in sched_core_fork(). sched_cgroup_fork() does nothing special. So it should be
kernel/fork.c +1 -1
@@ -2295,7 +2295,7 @@ __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
Sebastian
PATCH 1/1 futex: Use correct exit on failure from futex_hash_allocate_default()
In reply to Vlastimil Babkacopy_process() uses the wrong error exit path from futex_hash_allocate_default().
After exiting from futex_hash_allocate_default(), neither tasklist_lock nor siglock has been acquired. The exit label bad_fork_core_free unlocks both of these locks which is wrong.
The previous label, bad_fork_cancel_cgroup, is the correct exit. sched_cgroup_fork() did not allocate any resources that need to freed.
Use bad_fork_cancel_cgroup on error exit fromfutex_hash_allocate_default().
---
That private-futex code was marked BROKEN in v6.16 and re-enabled in v6.17. It could use
56180dd20c19e ("futex: Use RCU-based per-CPU reference counting instead of rcuref_t")
as Fixes: instead to avoid backporting to v6.16.
kernel/fork.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/fork.c +1 -1
@@ -2295,7 +2295,7 @@ __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
Signature · 1 line
2.51.0
Re: [PATCH] futex: Use correct exit on failure from futex_hash_allocate_default()
Quoted 11 lines · On Thu, 18 Sep 2025 15:09:45 +0200 Sebastian Andrzej Siewior…
copy_process()uses the wrong error exit path fromfutex_hash_allocate_default().
After exiting fromfutex_hash_allocate_default(), neithertasklist_locknor siglock has been acquired. The exit labelbad_fork_core_freeunlocks both of these locks which is wrong.The previous label,
bad_fork_cancel_cgroup, is the correct exit.sched_cgroup_fork()did not allocate any resources that need to freed.Use
bad_fork_cancel_cgroupon error exit fromfutex_hash_allocate_default().
if (need_futex_hash_allocate_default(clone_flags)) {
retval = futex_hash_allocate_default();
if (retval)
goto bad_fork_core_free;
[..]
}
[..]
write_lock_irq(&tasklist_lock);
[..]
klp_copy_process(p);
sched_core_fork(p);
spin_lock(¤t->sighand->siglock);
[..] bad_fork_core_free:
sched_core_free(p); spin_unlock(¤t->sighand->siglock); write_unlock_irq(&tasklist_lock); bad_fork_cancel_cgroup: cgroup_cancel_fork(p, args);
Yep, looks bad to me!
-- Steve
Quoted 6 lines
Fixes 7c4f75a21f636 ("futex: Allow automatic allocation of process wide futex hash")Reported-by [email protected]Signed-off-by Sebastian Andrzej Siewior <[email protected]>
[tip: locking/urgent] futex: Use correct exit on failure from futex_hash_allocate_default()
In reply to Sebastian Andrzej SiewiorThe following commit has been merged into the locking/urgent branch of tip:
The following commit has been merged into the locking/urgent branch of tip:
Commit-ID: 4ec3c15462b9f44562f45723a92e2807746ba7d1 Gitweb: https://git.kernel.org/tip/4ec3c15462b9f44562f45723a92e2807746ba7d1 Author: Sebastian Andrzej Siewior <[email protected]> AuthorDate: Thu, 18 Sep 2025 15:09:45 +02:00 Committer: Thomas Gleixner <[email protected]> CommitterDate: Wed, 24 Sep 2025 09:20:02 +02:00
futex: Use correct exit on failure from futex_hash_allocate_default()
copy_process() uses the wrong error exit path from futex_hash_allocate_default(). After exiting from futex_hash_allocate_default(), neither tasklist_lock nor siglock has been acquired. The exit label bad_fork_core_free unlocks both of these locks which is wrong.
The next exit label, bad_fork_cancel_cgroup, is the correct exit. sched_cgroup_fork() did not allocate any resources that need to freed.
Use bad_fork_cancel_cgroup on error exit from futex_hash_allocate_default().
--- kernel/fork.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
kernel/fork.c +1 -1
@@ -2295,7 +2295,7 @@ __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