[v6.6] possible deadlock in padata_do_serial

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: eac8889a3a1c Linux 6.6.140
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=14ca302e580000
kernel config: https://syzkaller.appspot.com/x/.config?x=c5b35c4db8465904
dashboard link: https://syzkaller.appspot.com/bug?extid=e3d4090c4aca807a9ac5
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/284081ee4b1a/disk-eac8889a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6503c72409ee/vmlinux-eac8889a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5e529dbebdcb/bzImage-eac8889a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e3d409...@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
kworker/u4:10/2996 is trying to acquire lock:
ffffe8ffffd53678 (&pd_list->lock){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffe8ffffd53678 (&pd_list->lock){+...}-{2:2}, at: padata_find_next kernel/padata.c:272 [inline]
ffffe8ffffd53678 (&pd_list->lock){+...}-{2:2}, at: padata_reorder kernel/padata.c:325 [inline]
ffffe8ffffd53678 (&pd_list->lock){+...}-{2:2}, at: padata_do_serial+0x644/0xa70 kernel/padata.c:395

but task is already holding lock:
ffffe8ffffd54620 (&pd_list->lock){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffe8ffffd54620 (&pd_list->lock){+...}-{2:2}, at: padata_reorder kernel/padata.c:316 [inline]
ffffe8ffffd54620 (&pd_list->lock){+...}-{2:2}, at: padata_do_serial+0x4db/0xa70 kernel/padata.c:395

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&pd_list->lock);
lock(&pd_list->lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by kworker/u4:10/2996:
#0: ffff88814567d138 ((wq_completion)pencrypt_parallel){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
#0: ffff88814567d138 ((wq_completion)pencrypt_parallel){+.+.}-{0:0}, at: process_scheduled_works+0x96f/0x15d0 kernel/workqueue.c:2730
#1: ffffc9000bf57d00 ((work_completion)(&pw->pw_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
#1: ffffc9000bf57d00 ((work_completion)(&pw->pw_work)){+.+.}-{0:0}, at: process_scheduled_works+0x96f/0x15d0 kernel/workqueue.c:2730
#2: ffffe8ffffd54620 (&pd_list->lock){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
#2: ffffe8ffffd54620 (&pd_list->lock){+...}-{2:2}, at: padata_reorder kernel/padata.c:316 [inline]
#2: ffffe8ffffd54620 (&pd_list->lock){+...}-{2:2}, at: padata_do_serial+0x4db/0xa70 kernel/padata.c:395

stack backtrace:
CPU: 1 PID: 2996 Comm: kworker/u4:10 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: pencrypt_parallel padata_parallel_worker
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
check_deadlock kernel/locking/lockdep.c:3062 [inline]
validate_chain kernel/locking/lockdep.c:3856 [inline]
__lock_acquire+0x5dbc/0x7d40 kernel/locking/lockdep.c:5137
lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
__raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
spin_lock include/linux/spinlock.h:351 [inline]
padata_find_next kernel/padata.c:272 [inline]
padata_reorder kernel/padata.c:325 [inline]
padata_do_serial+0x644/0xa70 kernel/padata.c:395
padata_parallel_worker+0x6f/0x1c0 kernel/padata.c:168
process_one_work kernel/workqueue.c:2653 [inline]
process_scheduled_works+0xa5d/0x15d0 kernel/workqueue.c:2730
worker_thread+0xa55/0xfc0 kernel/workqueue.c:2811
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>


---
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[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: 0a40c6fbd105 Linux 6.6.141
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=152a8a2e580000

kernel config: https://syzkaller.appspot.com/x/.config?x=c5b35c4db8465904
dashboard link: https://syzkaller.appspot.com/bug?extid=e3d4090c4aca807a9ac5
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13e636d2580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=142bfe2e580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/bef5f7e53495/disk-0a40c6fb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/61ce39aaab25/vmlinux-0a40c6fb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/43d2363e7871/bzImage-0a40c6fb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e3d409...@syzkaller.appspotmail.com

wlan0: Created IBSS using preconfigured BSSID 50:50:50:50:50:50
wlan0: Creating new IBSS network, BSSID 50:50:50:50:50:50

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------

kworker/u4:7/1085 is trying to acquire lock:
ffffe8ffffd265b0 (&pd_list->lock){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffe8ffffd265b0 (&pd_list->lock){+...}-{2:2}, at: padata_find_next kernel/padata.c:272 [inline]
ffffe8ffffd265b0 (&pd_list->lock){+...}-{2:2}, at: padata_reorder kernel/padata.c:325 [inline]
ffffe8ffffd265b0 (&pd_list->lock){+...}-{2:2}, at: padata_do_serial+0x644/0xa70 kernel/padata.c:395

but task is already holding lock:

ffffe8ffffc266a8 (&pd_list->lock){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffe8ffffc266a8 (&pd_list->lock){+...}-{2:2}, at: padata_reorder kernel/padata.c:316 [inline]
ffffe8ffffc266a8 (&pd_list->lock){+...}-{2:2}, at: padata_do_serial+0x4db/0xa70 kernel/padata.c:395

other info that might help us debug this:
Possible unsafe locking scenario:

CPU0
----
lock(&pd_list->lock);
lock(&pd_list->lock);

*** DEADLOCK ***

May be due to missing lock nesting notation

3 locks held by kworker/u4:7/1085:
#0: ffff88814005cd38 ((wq_completion)pencrypt_parallel){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
#0: ffff88814005cd38 ((wq_completion)pencrypt_parallel){+.+.}-{0:0}, at: process_scheduled_works+0x96f/0x15d0 kernel/workqueue.c:2730
#1: ffffc900049afd00 ((work_completion)(&pw->pw_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:2628 [inline]
#1: ffffc900049afd00 ((work_completion)(&pw->pw_work)){+.+.}-{0:0}, at: process_scheduled_works+0x96f/0x15d0 kernel/workqueue.c:2730
#2: ffffe8ffffc266a8 (&pd_list->lock){+...}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
#2: ffffe8ffffc266a8 (&pd_list->lock){+...}-{2:2}, at: padata_reorder kernel/padata.c:316 [inline]
#2: ffffe8ffffc266a8 (&pd_list->lock){+...}-{2:2}, at: padata_do_serial+0x4db/0xa70 kernel/padata.c:395

stack backtrace:
CPU: 0 PID: 1085 Comm: kworker/u4:7 Not tainted syzkaller #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Workqueue: pencrypt_parallel padata_parallel_worker
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
check_deadlock kernel/locking/lockdep.c:3062 [inline]
validate_chain kernel/locking/lockdep.c:3856 [inline]
__lock_acquire+0x5dbc/0x7d40 kernel/locking/lockdep.c:5137
lock_acquire+0x19e/0x420 kernel/locking/lockdep.c:5754
__raw_spin_lock include/linux/spinlock_api_smp.h:133 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:154
spin_lock include/linux/spinlock.h:351 [inline]
padata_find_next kernel/padata.c:272 [inline]
padata_reorder kernel/padata.c:325 [inline]
padata_do_serial+0x644/0xa70 kernel/padata.c:395
padata_parallel_worker+0x6f/0x1c0 kernel/padata.c:168
process_one_work kernel/workqueue.c:2653 [inline]
process_scheduled_works+0xa5d/0x15d0 kernel/workqueue.c:2730
worker_thread+0xa55/0xfc0 kernel/workqueue.c:2811
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>


---

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