Re: [PATCH] fcntl: make F_GETOWN(EX) return 0 on dead owner task

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Wed, Feb 03, 2021 at 03:41:56PM +0300, Pavel Tikhomirov wrote:
> Currently there is no way to differentiate the file with alive owner
> from the file with dead owner but pid of the owner reused. That's why
> CRIU can't actually know if it needs to restore file owner or not,
> because if it restores owner but actual owner was dead, this can
> introduce unexpected signals to the "false"-owner (which reused the
> pid).

Hi! Thanks for the patch. You know I manage to forget the fowner internals.
Could you please enlighten me -- when owner is set with some pid we do

f_setown_ex
  __f_setown
    f_modown
      filp->f_owner.pid = get_pid(pid);

Thus pid get refcount incremented. Then the owner exits but refcounter
should be still up and running and pid should not be reused, no? Or
I miss something obvious?

The patch itself looks ok on a first glance.