Re: [PATCH] pid: change task_struct::pid to read-only

From: Oleg Nesterov
Date: Tue Dec 17 2013 - 10:35:43 EST


On 12/16, Richard Guy Briggs wrote:
>
> task->pid is only ever assigned once (well ok, twice). For system health and
> secure logging confidence, make it const to make it much more intentional when
> it is being changed.

Hmm. I am a bit suprized you decided to constify task->pid, but OK.

And we can do the same with task->signal, this can actually help to generate
a better code, probably.

> if (!thread_group_leader(tsk)) {
> struct task_struct *leader = tsk->group_leader;
> + /* tast_struct::pid is const pid_t, hence the ugly cast */
> + pid_t *pid_p = (pid_t*)&(tsk->pid);
>
> sig->notify_count = -1; /* for exit_notify() */
> for (;;) {
> @@ -950,7 +952,7 @@ static int de_thread(struct task_struct *tsk)
> * Note: The old leader also uses this pid until release_task
> * is called. Odd but simple and correct.
> */
> - tsk->pid = leader->pid;
> + *pid_p = leader->pid;

Well, imho this (and de_thread) looks a bit ugly. Perhaps we should add
something like

#define ASSIGN_CONST(l, r) (*(typeof(r) *)&(l) = (r))

into compiler.h ?

Oleg.

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