============================================
WARNING: possible recursive locking detected
5.9.0-rc2-next-20200828-syzkaller #0 Not tainted
--------------------------------------------
syz-executor.3/21064 is trying to acquire lock:
ffff88804bd05498 (&sighand->siglock){-.-.}-{2:2}, at: __lock_task_sighand+0x106/0x2d0 kernel/signal.c:1390

but task is already holding lock:
ffff88804bd05498 (&sighand->siglock){-.-.}-{2:2}, at: __lock_task_sighand+0x106/0x2d0 kernel/signal.c:1390

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

4 locks held by syz-executor.3/21064:
 #0: ffff8880a10b2868 (&pipe->mutex/1){+.+.}-{3:3}, at: __pipe_lock fs/pipe.c:87 [inline]
 #0: ffff8880a10b2868 (&pipe->mutex/1){+.+.}-{3:3}, at: pipe_write+0x5bd/0x16c0 fs/pipe.c:580
 #1: ffff88804bd05498 (&sighand->siglock){-.-.}-{2:2}, at: __lock_task_sighand+0x106/0x2d0 kernel/signal.c:1390
 #2: ffff88804bd054e0 (&sighand->signalfd_wqh){....}-{2:2}, at: __wake_up_common_lock+0xb4/0x130 kernel/sched/wait.c:122
 #3: ffffffff89c67640 (rcu_read_lock){....}-{1:2}, at: __lock_task_sighand+0x0/0x2d0 kernel/signal.c:1352

stack backtrace:
CPU: 0 PID: 21064 Comm: syz-executor.3 Not tainted 5.9.0-rc2-next-20200828-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
 do_send_sig_info kernel/signal.c:1290 [inline]
 send_sig_info kernel/signal.c:1605 [inline]
 send_sig+0xcb/0x160 kernel/signal.c:1615
 pipe_write+0x1114/0x16c0 fs/pipe.c:489
 call_write_iter include/linux/fs.h:1892 [inline]
 new_sync_write+0x422/0x650 fs/read_write.c:503
 vfs_write+0x5ad/0x730 fs/read_write.c:578
 ksys_write+0x1ee/0x250 fs/read_write.c:631
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d5b9
Code: 5d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f9d9bbdcc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 0000000000038b80 RCX: 000000000045d5b9
RDX: 00000000fffffd88 RSI: 0000000020000000 RDI: 0000000000000008
RBP: 000000000118cf80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007ffcf810cd7f R14: 00007f9d9bbdd9c0 R15: 000000000118cf4c