======================================================
WARNING: possible circular locking dependency detected
4.14.97+ #4 Not tainted
------------------------------------------------------
syz-executor2/10338 is trying to acquire lock:
 (&sig->cred_guard_mutex){+.+.}, at: [<ffffffff9269e892>] proc_pid_attr_write+0x152/0x280 fs/proc/base.c:2590

but task is already holding lock:
 (&pipe->mutex/1){+.+.}, at: [<ffffffff9256f128>] pipe_lock_nested fs/pipe.c:67 [inline]
 (&pipe->mutex/1){+.+.}, at: [<ffffffff9256f128>] pipe_lock+0x58/0x70 fs/pipe.c:75

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&pipe->mutex/1){+.+.}:

-> #0 (&sig->cred_guard_mutex){+.+.}:

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&pipe->mutex/1);
                               lock(&sig->cred_guard_mutex);
                               lock(&pipe->mutex/1);
  lock(&sig->cred_guard_mutex);

 *** DEADLOCK ***

2 locks held by syz-executor2/10338:
 #0:  (sb_writers#7){.+.+}, at: [<ffffffff925fa741>] file_start_write include/linux/fs.h:2726 [inline]
 #0:  (sb_writers#7){.+.+}, at: [<ffffffff925fa741>] do_splice fs/splice.c:1146 [inline]
 #0:  (sb_writers#7){.+.+}, at: [<ffffffff925fa741>] SYSC_splice fs/splice.c:1402 [inline]
 #0:  (sb_writers#7){.+.+}, at: [<ffffffff925fa741>] SyS_splice+0xec1/0x12d0 fs/splice.c:1382
 #1:  (&pipe->mutex/1){+.+.}, at: [<ffffffff9256f128>] pipe_lock_nested fs/pipe.c:67 [inline]
 #1:  (&pipe->mutex/1){+.+.}, at: [<ffffffff9256f128>] pipe_lock+0x58/0x70 fs/pipe.c:75

stack backtrace:
CPU: 0 PID: 10338 Comm: syz-executor2 Not tainted 4.14.97+ #4
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0xb9/0x10e lib/dump_stack.c:53
 print_circular_bug.isra.0.cold+0x2dc/0x425 kernel/locking/lockdep.c:1258
input: syz0 as /devices/virtual/input/input15
input: syz0 as /devices/virtual/input/input16
input: syz0 as /devices/virtual/input/input17
input: syz0 as /devices/virtual/input/input18
input: syz0 as /devices/virtual/input/input19
input: syz0 as /devices/virtual/input/input20
input: syz0 as /devices/virtual/input/input21
input: syz0 as /devices/virtual/input/input22
input: syz0 as /devices/virtual/input/input23
input: syz0 as /devices/virtual/input/input24