======================================================
WARNING: possible circular locking dependency detected
4.15.0-rc5+ #237 Not tainted
------------------------------------------------------
syzkaller128024/3156 is trying to acquire lock:
 (&p->lock){+.+.}, at: [<00000000d799377f>] seq_read+0xd5/0x13d0 fs/seq_file.c:165

but task is already holding lock:
 (&pipe->mutex/1){+.+.}, at: [<00000000c4279ecd>] pipe_lock_nested fs/pipe.c:67 [inline]
 (&pipe->mutex/1){+.+.}, at: [<00000000c4279ecd>] pipe_lock+0x56/0x70 fs/pipe.c:75

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&pipe->mutex/1){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
       __pipe_lock fs/pipe.c:88 [inline]
       fifo_open+0x15c/0xa30 fs/pipe.c:916
       do_dentry_open+0x667/0xd40 fs/open.c:752
       vfs_open+0x107/0x220 fs/open.c:866
       do_last fs/namei.c:3379 [inline]
       path_openat+0x1151/0x3530 fs/namei.c:3519
       do_filp_open+0x25b/0x3b0 fs/namei.c:3554
       do_open_execat+0x1b9/0x5c0 fs/exec.c:849
       do_execveat_common.isra.30+0x90c/0x23c0 fs/exec.c:1735
       do_execve fs/exec.c:1842 [inline]
       SYSC_execve fs/exec.c:1923 [inline]
       SyS_execve+0x39/0x50 fs/exec.c:1918
       do_syscall_64+0x26c/0x920 arch/x86/entry/common.c:285
       return_from_SYSCALL_64+0x0/0x75

-> #1 (&sig->cred_guard_mutex){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
       mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:923
       lock_trace+0x44/0xc0 fs/proc/base.c:405
       proc_pid_syscall+0xa3/0x550 fs/proc/base.c:622
       proc_single_show+0xf8/0x170 fs/proc/base.c:744
       seq_read+0x385/0x13d0 fs/seq_file.c:234
       do_loop_readv_writev fs/read_write.c:673 [inline]
       do_iter_read+0x3d2/0x5a0 fs/read_write.c:897
       vfs_readv+0x121/0x1c0 fs/read_write.c:959
       do_readv+0xfc/0x2a0 fs/read_write.c:992
       SYSC_readv fs/read_write.c:1079 [inline]
       SyS_readv+0x27/0x30 fs/read_write.c:1076
       entry_SYSCALL_64_fastpath+0x1f/0x96

-> #0 (&p->lock){+.+.}:
       lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3914
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
       seq_read+0xd5/0x13d0 fs/seq_file.c:165
       proc_reg_read+0xef/0x170 fs/proc/inode.c:217
       do_loop_readv_writev fs/read_write.c:673 [inline]
       do_iter_read+0x3d2/0x5a0 fs/read_write.c:897
       vfs_readv+0x121/0x1c0 fs/read_write.c:959
       kernel_readv fs/splice.c:361 [inline]
       default_file_splice_read+0x508/0xae0 fs/splice.c:416
       do_splice_to+0x10a/0x160 fs/splice.c:880
       do_splice fs/splice.c:1173 [inline]
       SYSC_splice fs/splice.c:1402 [inline]
       SyS_splice+0x1187/0x1610 fs/splice.c:1382
       entry_SYSCALL_64_fastpath+0x1f/0x96

other info that might help us debug this:

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

 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 syzkaller128024/3156:
 #0:  (&pipe->mutex/1){+.+.}, at: [<00000000c4279ecd>] pipe_lock_nested fs/pipe.c:67 [inline]
 #0:  (&pipe->mutex/1){+.+.}, at: [<00000000c4279ecd>] pipe_lock+0x56/0x70 fs/pipe.c:75

stack backtrace:
CPU: 1 PID: 3156 Comm: syzkaller128024 Not tainted 4.15.0-rc5+ #237
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x194/0x257 lib/dump_stack.c:53
 print_circular_bug.isra.37+0x2cd/0x2dc kernel/locking/lockdep.c:1218
 check_prev_add kernel/locking/lockdep.c:1858 [inline]
 check_prevs_add kernel/locking/lockdep.c:1971 [inline]
 validate_chain kernel/locking/lockdep.c:2412 [inline]
 __lock_acquire+0x30a8/0x3e00 kernel/locking/lockdep.c:3426
 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:3914
 __mutex_lock_common kernel/locking/mutex.c:756 [inline]
 __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908
 seq_read+0xd5/0x13d0 fs/seq_file.c:165
 proc_reg_read+0xef/0x170 fs/proc/inode.c:217
 do_loop_readv_writev fs/read_write.c:673 [inline]
 do_iter_read+0x3d2/0x5a0 fs/read_write.c:897
 vfs_readv+0x121/0x1c0 fs/read_write.c:959
 kernel_readv fs/splice.c:361 [inline]
 default_file_splice_read+0x508/0xae0 fs/splice.c:416
 do_splice_to+0x10a/0x160 fs/splice.c:880
 do_splice fs/splice.c:1173 [inline]
 SYSC_splice fs/splice.c:1402 [inline]
 SyS_splice+0x1187/0x1610 fs/splice.c:1382
 entry_SYSCALL_64_fastpath+0x1f/0x96
RIP: 0033:0x446059
RSP: 002b:00007fac5f985d08 EFLAGS: 00000216 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00000000006f0054 RCX: 0000000000446059
RDX: 0000000000000006 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00000000006f0050 R08: 0000000000000004 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000216 R12: 00007fac5f985d20
R13: 702f7465