Re: [RFC 1/2] proc: Return if nothing to unmount

[Al Viro]

On Sat, Sep 09, 2017 at 06:03:16PM +0530, Gargi Sharma wrote:
> If a task exits before procfs is mounted, proc_flush_task_mnt will
> be called with a NULL mnt parameter. In that case, not only is there
> nothing to unhash, but trying to do so will oops the kernel with a
> null pointer dereference.

You are misreading that sucker.  It's about userland mounts, it's about
the internal ones in pidns, for each pidns the process belongs to.

IOW, what you are adding is dead code.  The very first alloc_pid() in
that pidns should've called pid_ns_prepare_proc(), which creates that
vfsmount.