Kernel bug: possible deadlock in padata_do_serial
Subsystem: crypto
Status: fixed

Crash report:
============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
kworker/u32:5/96 is trying to acquire lock:
ffffe8fefc53dbc8 (&pd_list->lock){+...}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffe8fefc53dbc8 (&pd_list->lock){+...}-{3:3}, at: padata_find_next kernel/padata.c:256 [inline]
ffffe8fefc53dbc8 (&pd_list->lock){+...}-{3:3}, at: padata_reorder kernel/padata.c:309 [inline]
ffffe8fefc53dbc8 (&pd_list->lock){+...}-{3:3}, at: padata_do_serial+0x7bd/0xd20 kernel/padata.c:379

but task is already holding lock:
ffffe8fefc53dc18 (&pd_list->lock){+...}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
ffffe8fefc53dc18 (&pd_list->lock){+...}-{3:3}, at: padata_reorder kernel/padata.c:300 [inline]
ffffe8fefc53dc18 (&pd_list->lock){+...}-{3:3}, at: padata_do_serial+0x697/0xd20 kernel/padata.c:379

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/u32:5/96:
 #0: ffff888022495148 ((wq_completion)pdecrypt_parallel){+.+.}-{0:0}, at: process_one_work+0x12a2/0x1b70 kernel/workqueue.c:3211
 #1: ffffc9000167fd10 ((work_completion)(&pw->pw_work)){+.+.}-{0:0}, at: process_one_work+0x929/0x1b70 kernel/workqueue.c:3212
 #2: ffffe8fefc53dc18 (&pd_list->lock){+...}-{3:3}, at: spin_lock include/linux/spinlock.h:351 [inline]
 #2: ffffe8fefc53dc18 (&pd_list->lock){+...}-{3:3}, at: padata_reorder kernel/padata.c:300 [inline]
 #2: ffffe8fefc53dc18 (&pd_list->lock){+...}-{3:3}, at: padata_do_serial+0x697/0xd20 kernel/padata.c:379

stack backtrace:
CPU: 2 UID: 0 PID: 96 Comm: kworker/u32:5 Not tainted syzkaller #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
Workqueue: pdecrypt_parallel padata_parallel_worker
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_deadlock_bug+0x1e9/0x240 kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain kernel/locking/lockdep.c:3895 [inline]
 __lock_acquire+0x1133/0x1ce0 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x179/0x350 kernel/locking/lockdep.c:5825
 __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:256 [inline]
 padata_reorder kernel/padata.c:309 [inline]
 padata_do_serial+0x7bd/0xd20 kernel/padata.c:379
 pcrypt_aead_dec+0x5b/0x70 crypto/pcrypt.c:140
 padata_parallel_worker+0x62/0xb0 kernel/padata.c:157
 process_one_work+0x9cc/0x1b70 kernel/workqueue.c:3236
 process_scheduled_works kernel/workqueue.c:3319 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3400
 kthread+0x3c2/0x780 kernel/kthread.c:463
 ret_from_fork+0x56a/0x730 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>