============================================
WARNING: possible recursive locking detected
5.9.0-rc2-next-20200825-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.1/21003 is trying to acquire lock:
ffff88804e160c58 (&sighand->siglock){-...}-{2:2}, at: __lock_task_sighand+0x106/0x2d0 kernel/signal.c:1390

but task is already holding lock:
ffff88804e160c58 (&sighand->siglock){-...}-{2:2}, at: force_sig_info_to_task+0x6c/0x3a0 kernel/signal.c:1316

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

       CPU0
       ----
  lock(&sighand->siglock);
  lock(&sighand->siglock);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by syz-executor.1/21003:
 #0: ffff88804e160c58 (&sighand->siglock){-...}-{2:2}, at: force_sig_info_to_task+0x6c/0x3a0 kernel/signal.c:1316
 #1: ffff88804e160ca0 (&sighand->signalfd_wqh){....}-{2:2}, at: __wake_up_common_lock+0xb4/0x130 kernel/sched/wait.c:122
 #2: ffffffff89c675c0 (rcu_read_lock){....}-{1:2}, at: __lock_task_sighand+0x0/0x2d0 kernel/signal.c:1352

stack backtrace:
CPU: 1 PID: 21003 Comm: syz-executor.1 Not tainted 5.9.0-rc2-next-20200825-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x18f/0x20d lib/dump_stack.c:118
 print_deadlock_bug kernel/locking/lockdep.c:2391 [inline]
 check_deadlock kernel/locking/lockdep.c:2432 [inline]
 validate_chain kernel/locking/lockdep.c:3202 [inline]
 __lock_acquire.cold+0x115/0x396 kernel/locking/lockdep.c:4426
 lock_acquire+0x1f1/0xad0 kernel/locking/lockdep.c:5005
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x8c/0xc0 kernel/locking/spinlock.c:159
 __lock_task_sighand+0x106/0x2d0 kernel/signal.c:1390
 lock_task_sighand include/linux/sched/signal.h:687 [inline]
 task_work_add+0x1d7/0x290 kernel/task_work.c:51
 io_req_task_work_add fs/io_uring.c:1765 [inline]
 __io_async_wake+0x415/0x980 fs/io_uring.c:4589
 __wake_up_common+0x147/0x650 kernel/sched/wait.c:93
 __wake_up_common_lock+0xd0/0x130 kernel/sched/wait.c:123
 signalfd_notify include/linux/signalfd.h:22 [inline]
 __send_signal+0x75b/0xf90 kernel/signal.c:1163
 force_sig_info_to_task+0x2a0/0x3a0 kernel/signal.c:1333
 force_sig_fault_to_task kernel/signal.c:1672 [inline]
 force_sig_fault+0xb0/0xf0 kernel/signal.c:1679
 __bad_area_nosemaphore+0x32a/0x480 arch/x86/mm/fault.c:778
 do_user_addr_fault+0x852/0xbf0 arch/x86/mm/fault.c:1257
 handle_page_fault arch/x86/mm/fault.c:1351 [inline]
 exc_page_fault+0xa8/0x160 arch/x86/mm/fault.c:1404
 asm_exc_page_fault+0x1e/0x30 arch/x86/include/asm/idtentry.h:538
RIP: 0033:0x45717f
Code: bc d1 f3 0f 7f 27 f3 0f 7f 6f 10 f3 0f 7f 77 20 f3 0f 7f 7f 30 49 83 c0 0f 49 29 d0 48 8d 7c 17 31 e9 95 0b 00 00 66 0f ef c0 <f3> 0f 6f 0e f3 0f 6f 56 10 66 0f 74 c1 66 0f d7 d0 49 83 f8 11 0f
RSP: 002b:00007f6888e9a9c8 EFLAGS: 00010283
RAX: 00007f6888e9aa58 RBX: 00007f6888e9aa40 RCX: 0000000000000000
RDX: 0000000000000010 RSI: 0000000000000000 RDI: 00007f6888e9aa58
RBP: 000000000118d010 R08: 0000000000000010 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6888e9aa58
R13: 00007fff912081ff R14: 00007f6888e9b9c0 R15: 000000000118cfec