Merge tag 'for-linus-20190627' of gitolite.kernel.org:pub/scm/linux/kernel/git/brauner/linux

Pull pidfd fixes from Christian Brauner:
 "Userspace tools and libraries such as strace or glibc need a cheap and
  reliable way to tell whether CLONE_PIDFD is supported. The easiest way
  is to pass an invalid fd value in the return argument, perform the
  syscall and verify the value in the return argument has been changed
  to a valid fd.

  However, if CLONE_PIDFD is specified we currently check if pidfd == 0
  and return EINVAL if not.

  The check for pidfd == 0 was originally added to enable us to abuse
  the return argument for passing additional flags along with
  CLONE_PIDFD in the future.

  However, extending legacy clone this way would be a terrible idea and
  with clone3 on the horizon and the ability to reuse CLONE_DETACHED
  with CLONE_PIDFD there's no real need for this clutch. So remove the
  pidfd == 0 check and help userspace out.

  Also, accordig to Al, anon_inode_getfd() should only be used past the
  point of no failure and ksys_close() should not be used at all since
  it is far too easy to get wrong. Al's motto being "basically, once
  it's in descriptor table, it's out of your control". So Al's patch
  switches back to what we already had in v1 of the original patchset
  and uses a anon_inode_getfile() + put_user() + fd_install() sequence
  in the success path and a fput() + put_unused_fd() in the failure
  path.

  The other two changes should be trivial"

* tag 'for-linus-20190627' of gitolite.kernel.org:pub/scm/linux/kernel/git/brauner/linux:
  proc: remove useless d_is_dir() check
  copy_process(): don't use ksys_close() on cleanups
  samples: make pidfd-metadata fail gracefully on older kernels
  fork: don't check parent_tidptr with CLONE_PIDFD

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