======================================================
WARNING: possible circular locking dependency detected
4.14.108+ #36 Not tainted
------------------------------------------------------
syz-executor.4/7032 is trying to acquire lock:
 (&sig->cred_guard_mutex){+.+.}, at: [<ffffffff8c0a39df>] lock_trace+0x3f/0xc0 fs/proc/base.c:408

but task is already holding lock:
 (&p->lock){+.+.}, at: [<ffffffff8bfcf95d>] seq_read+0xcd/0x1180 fs/seq_file.c:165

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&p->lock){+.+.}:

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

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

other info that might help us debug this:

Chain exists of:
  &sig->cred_guard_mutex --> &pipe->mutex/1 --> &p->lock

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by syz-executor.4/7032:
 #0:  (sb_writers#7){.+.+}, at: [<ffffffff8bf58e3f>] file_start_write include/linux/fs.h:2726 [inline]
 #0:  (sb_writers#7){.+.+}, at: [<ffffffff8bf58e3f>] do_sendfile+0x88f/0xb20 fs/read_write.c:1437
 #1:  (&p->lock){+.+.}, at: [<ffffffff8bfcf95d>] seq_read+0xcd/0x1180 fs/seq_file.c:165

stack backtrace:
CPU: 0 PID: 7032 Comm: syz-executor.4 Not tainted 4.14.108+ #36
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