[RFC PATCH 00/12 v3] ptrace: introduce task_struct->ptrace_cxt

[Oleg Nesterov <oleg@redhat.com>]

Changes:

	04/12:	move kfree() outside of task_lock() in alloc_ptrace_context().
		But I misread your sugesstion:

			>       task_lock(tsk);
			>       if (likely(!tsk->ptrace_ctx)) {
			>               tsk->ptrace_ctx = ptrace_ctx;
			>               task_unlock(tsk);
			>               return 0;
			>       }
			>
			>       task_unlock(tsk);
			>       kfree(ptrace_ctx);

		Just can't do that. I hate multiple unlocks very much. So it
		becomes:

			task_lock(tsk);
			if (likely(!tsk->ptrace_ctx)) {
				tsk->ptrace_ctx = ptrace_ctx;
				ptrace_ctx = NULL;
			}
			task_unlock(tsk);
			kfree(ptrace_ctx);

		kfree(NULL) is specially allowed.


	05/12:	Add the comment about tracehook_init_task to ptrace_init_task().

		I didn't change the original comment, but imho it is confusing.
		"immediately after adding @child to its parent's children list"
		does not matter. What does matter, is that it is called before
		this child is visible to the user-space and thus the unconditional
		ptrace_link() is safe: nobody could attach before us.


	08/12:	No changes, but I think it better to change format_mca_init_stack()
		right now. Imho it has nothing to do with tracehooks and it is the
		last user of ->parent (except perhaps there are some in arch/ code
		which should be tracehookfied).


	09/12:	Remove the stale "pt_" from the changelog.

Oleg.