======================================================
[ INFO: possible circular locking dependency detected ]
4.9.71-g2506378 #113 Not tainted
-------------------------------------------------------
syzkaller943582/3336 is trying to acquire lock:
 (&p->lock){+.+.+.}, at: [<ffffffff815e651d>] seq_read+0xdd/0x1290 fs/seq_file.c:178
but task is already holding lock:
 (&pipe->mutex/1){+.+.+.}, at: [<ffffffff815866a6>] pipe_lock_nested fs/pipe.c:66 [inline]
 (&pipe->mutex/1){+.+.+.}, at: [<ffffffff815866a6>] pipe_lock+0x56/0x70 fs/pipe.c:74
which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

       lock_acquire+0x12e/0x410 kernel/locking/lockdep.c:3756
       __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       mutex_lock_nested+0xbb/0x870 kernel/locking/mutex.c:621
       __pipe_lock fs/pipe.c:87 [inline]
       fifo_open+0x15c/0xa30 fs/pipe.c:916
       do_dentry_open+0x607/0xc60 fs/open.c:766
       vfs_open+0x105/0x220 fs/open.c:879
       do_last fs/namei.c:3408 [inline]
       path_openat+0x5ac/0x2910 fs/namei.c:3531
       do_filp_open+0x197/0x290 fs/namei.c:3566
       do_open_execat+0xfa/0x4d0 fs/exec.c:844
       do_execveat_common.isra.37+0x6d6/0x1f10 fs/exec.c:1724
       do_execve fs/exec.c:1830 [inline]
       SYSC_execve fs/exec.c:1911 [inline]
       SyS_execve+0x42/0x50 fs/exec.c:1906
       do_syscall_64+0x197/0x490 arch/x86/entry/common.c:280
       return_from_SYSCALL_64+0x0/0x7a

       lock_acquire+0x12e/0x410 kernel/locking/lockdep.c:3756
       __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       mutex_lock_killable_nested+0xcc/0x960 kernel/locking/mutex.c:641
       lock_trace+0x44/0xc0 fs/proc/base.c:428
       proc_pid_syscall+0xa6/0x260 fs/proc/base.c:646
       proc_single_show+0xf8/0x170 fs/proc/base.c:768
       seq_read+0x32f/0x1290 fs/seq_file.c:240
       do_loop_readv_writev.part.17+0x141/0x1e0 fs/read_write.c:714
       do_loop_readv_writev fs/read_write.c:880 [inline]
       do_readv_writev+0x520/0x750 fs/read_write.c:874
       vfs_readv+0x84/0xc0 fs/read_write.c:898
       do_readv+0xe6/0x250 fs/read_write.c:924
       SYSC_readv fs/read_write.c:1011 [inline]
       SyS_readv+0x27/0x30 fs/read_write.c:1008
       entry_SYSCALL_64_fastpath+0x23/0xc6

       check_prev_add kernel/locking/lockdep.c:1828 [inline]
       check_prevs_add kernel/locking/lockdep.c:1938 [inline]
       validate_chain kernel/locking/lockdep.c:2265 [inline]
       __lock_acquire+0x2bf9/0x3640 kernel/locking/lockdep.c:3345
       lock_acquire+0x12e/0x410 kernel/locking/lockdep.c:3756
       __mutex_lock_common kernel/locking/mutex.c:521 [inline]
       mutex_lock_nested+0xbb/0x870 kernel/locking/mutex.c:621
       seq_read+0xdd/0x1290 fs/seq_file.c:178
       proc_reg_read+0xef/0x170 fs/proc/inode.c:202
       do_loop_readv_writev.part.17+0x141/0x1e0 fs/read_write.c:714
       do_loop_readv_writev fs/read_write.c:880 [inline]
       do_readv_writev+0x520/0x750 fs/read_write.c:874
       vfs_readv+0x84/0xc0 fs/read_write.c:898
       kernel_readv fs/splice.c:363 [inline]
       default_file_splice_read+0x43f/0x7a0 fs/splice.c:435
       do_splice_to+0x10a/0x160 fs/splice.c:899
       do_splice fs/splice.c:1192 [inline]
       SYSC_splice fs/splice.c:1416 [inline]
       SyS_splice+0xf5f/0x1520 fs/splice.c:1399
       entry_SYSCALL_64_fastpath+0x23/0xc6

other info that might help us debug this:

Chain exists of:
 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

1 lock held by syzkaller943582/3336:
 #0:  (&pipe->mutex/1){+.+.+.}, at: [<ffffffff815866a6>] pipe_lock_nested fs/pipe.c:66 [inline]
 #0:  (&pipe->mutex/1){+.+.+.}, at: [<ffffffff815866a6>] pipe_lock+0x56/0x70 fs/pipe.c:74

stack backtrace:
CPU: 0 PID: 3336 Comm: syzkaller943582 Not tainted 4.9.71-g2506378 #113
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801c80972b8 ffffffff81d922b9 ffffffff85363ea0 ffffffff853983a0
 ffffffff8539e3d0 ffff8801ca9cb8d8 ffff8801ca9cb000 ffff8801c8097300
 ffffffff812367e1 ffff8801ca9cb8d8 00000000ca9cb8b0 ffff8801ca9cb8d8
Call Trace:
 [<ffffffff81d922b9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d922b9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff812367e1>] print_circular_bug+0x271/0x310 kernel/locking/lockdep.c:1202
 [<ffffffff8123cc19>] check_prev_add kernel/locking/lockdep.c:1828 [inline]
 [<ffffffff8123cc19>] check_prevs_add kernel/locking/lockdep.c:1938 [inline]
 [<ffffffff8123cc19>] validate_chain kernel/locking/lockdep.c:2265 [inline]
 [<ffffffff8123cc19>] __lock_acquire+0x2bf9/0x3640 kernel/locking/lockdep.c:3345
 [<ffffffff8123e09e>] lock_acquire+0x12e/0x410 kernel/locking/lockdep.c:3756
 [<ffffffff838a52eb>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff838a52eb>] mutex_lock_nested+0xbb/0x870 kernel/locking/mutex.c:621
 [<ffffffff815e651d>] seq_read+0xdd/0x1290 fs/seq_file.c:178
 [<ffffffff816bfbbf>] proc_reg_read+0xef/0x170 fs/proc/inode.c:202
 [<ffffffff8156a4e1>] do_loop_readv_writev.part.17+0x141/0x1e0 fs/read_write.c:714
 [<ffffffff8156e350>] do_loop_readv_writev fs/read_write.c:880 [inline]
 [<ffffffff8156e350>] do_readv_writev+0x520/0x750 fs/read_write.c:874
 [<ffffffff8156e604>] vfs_readv+0x84/0xc0 fs/read_write.c:898
 [<ffffffff8160d6bf>] kernel_readv fs/splice.c:363 [inline]
 [<ffffffff8160d6bf>] default_file_splice_read+0x43f/0x7a0 fs/splice.c:435
 [<ffffffff8160c7ba>] do_splice_to+0x10a/0x160 fs/splice.c:899
 [<ffffffff8161252f>] do_splice fs/splice.c:1192 [inline]
 [<ffffffff8161252f>] SYSC_splice fs/splice.c:1416 [inline]
 [<ffffffff8161252f>] SyS_splice+0xf5f/0x1520 fs/splice.c:1399
 [<ffffffff838aef85>] entry_SYSCALL_64_fastpath+0x23/0xc6