[PATCH v2 0/4] proc: first_tid() fix/cleanup

[Oleg Nesterov <oleg@redhat.com>]

Hello.

next_thread() should be avoided, probably next_tid() is the
only "valid" user.

But now we have another reason to avoid (and probably even kill)
it, we are going to replace or fix while_each_thread(), almost
every lockless usage is wrong.

Changes:

	1/4: Update the changelog, do not move the comment.

	2/4: No changes.

	3/4: Update the comment following the explanations from
	     Eric.

	     Eric pointed that get_proc_task() without rcu lock
	     can trigger the (bogus) warning. Extract the similar
	     check from pid_delete_dentry() into the new helper
	     and use it instead.

	     I didn't dare to preserve his ack, but the only change
	     is the new proc_inode_is_dead() helper and

		- if (pid_task(proc_pid(inode))
		+ if (proc_inode_is_dead(inode))

	     in proc_task_readdir().

	4/4: New.

Oleg.