======================================================
WARNING: possible circular locking dependency detected
4.14.95+ #16 Not tainted
------------------------------------------------------
syz-executor2/19998 is trying to acquire lock:
 (&pipe->mutex/1){+.+.}, at: [<ffffffff94371f86>] __pipe_lock fs/pipe.c:88 [inline]
 (&pipe->mutex/1){+.+.}, at: [<ffffffff94371f86>] fifo_open+0x156/0x9b0 fs/pipe.c:921

but task is already holding lock:
 (&sig->cred_guard_mutex){+.+.}, at: [<ffffffff9436c3a1>] prepare_bprm_creds+0x51/0x110 fs/exec.c:1389

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&sig->cred_guard_mutex){+.+.}:

-> #0 (&pipe->mutex/1){+.+.}:

other info that might help us debug this:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syz-executor2/19998:
 #0:  (&sig->cred_guard_mutex){+.+.}, at: [<ffffffff9436c3a1>] prepare_bprm_creds+0x51/0x110 fs/exec.c:1389

stack backtrace:
CPU: 0 PID: 19998 Comm: syz-executor2 Not tainted 4.14.95+ #16
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
EXT4-fs: 8 callbacks suppressed
EXT4-fs (sda1): changing journal_checksum during remount not supported; ignoring
EXT4-fs (sda1): re-mounted. Opts: journal_async_commit,
EXT4-fs (sda1): changing journal_checksum during remount not supported; ignoring
EXT4-fs (sda1): re-mounted. Opts: journal_async_commit,
EXT4-fs (sda1): Ignoring removed oldalloc option
EXT4-fs (sda1): Unrecognized mount option "fowner<00000000000000000000" or missing value
EXT4-fs (sda1): changing journal_checksum during remount not supported; ignoring
EXT4-fs (sda1): re-mounted. Opts: journal_async_commit,
EXT4-fs (sda1): Ignoring removed oldalloc option
EXT4-fs (sda1): Unrecognized mount option "fowner<00000000000000000000" or missing value
audit: type=1400 audit(1548342511.901:45): avc:  denied  { map } for  pid=20238 comm="syz-executor5" path="/proc/20238/fdinfo" dev="proc" ino=56644 scontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tcontext=unconfined_u:system_r:insmod_t:s0-s0:c0.c1023 tclass=dir permissive=1
mmap: syz-executor5 (20465) uses deprecated remap_file_pages() syscall. See Documentation/vm/remap_file_pages.txt.