Re: [rfc][patch] Avoid taking global tasklist_lock for single threadedprocess at getrusage()

[Oleg Nesterov <oleg@tv-sign.ru>]

Ravikiran G Thirumalai wrote:
>
> +       need_lock = (p == current && thread_group_empty(p));

This should be

	need_lock = !(p == current && thread_group_empty(p));


I think we should cleanup k_getrusage() first, see the patch below.

Do you agree with that patch? If yes, could you make the new one on
top of it? (please send them both to Andrew).

Note that after this cleanup we don't have code duplication.


[PATCH] simplify k_getrusage()

Factor out common code for different RUSAGE_xxx cases.

Don't take ->sighand->siglock in RUSAGE_SELF case, suggested
by Ravikiran G Thirumalai.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>

--- K/kernel/sys.c~	2006-01-03 21:15:58.000000000 +0300
+++ K/kernel/sys.c	2006-01-06 00:40:34.000000000 +0300
@@ -1687,7 +1687,10 @@ static void k_getrusage(struct task_stru
 	if (unlikely(!p->signal))
 		return;
 
+	utime = stime = cputime_zero;
+
 	switch (who) {
+		case RUSAGE_BOTH:
 		case RUSAGE_CHILDREN:
 			spin_lock_irqsave(&p->sighand->siglock, flags);
 			utime = p->signal->cutime;
@@ -1697,22 +1700,11 @@ static void k_getrusage(struct task_stru
 			r->ru_minflt = p->signal->cmin_flt;
 			r->ru_majflt = p->signal->cmaj_flt;
 			spin_unlock_irqrestore(&p->sighand->siglock, flags);
-			cputime_to_timeval(utime, &r->ru_utime);
-			cputime_to_timeval(stime, &r->ru_stime);
-			break;
+
+			if (who == RUSAGE_CHILDREN)
+				break;
+
 		case RUSAGE_SELF:
-			spin_lock_irqsave(&p->sighand->siglock, flags);
-			utime = stime = cputime_zero;
-			goto sum_group;
-		case RUSAGE_BOTH:
-			spin_lock_irqsave(&p->sighand->siglock, flags);
-			utime = p->signal->cutime;
-			stime = p->signal->cstime;
-			r->ru_nvcsw = p->signal->cnvcsw;
-			r->ru_nivcsw = p->signal->cnivcsw;
-			r->ru_minflt = p->signal->cmin_flt;
-			r->ru_majflt = p->signal->cmaj_flt;
-		sum_group:
 			utime = cputime_add(utime, p->signal->utime);
 			stime = cputime_add(stime, p->signal->stime);
 			r->ru_nvcsw += p->signal->nvcsw;
@@ -1729,13 +1721,14 @@ static void k_getrusage(struct task_stru
 				r->ru_majflt += t->maj_flt;
 				t = next_thread(t);
 			} while (t != p);
-			spin_unlock_irqrestore(&p->sighand->siglock, flags);
-			cputime_to_timeval(utime, &r->ru_utime);
-			cputime_to_timeval(stime, &r->ru_stime);
 			break;
+
 		default:
 			BUG();
 	}
+
+	cputime_to_timeval(utime, &r->ru_utime);
+	cputime_to_timeval(stime, &r->ru_stime);
 }
 
 int getrusage(struct task_struct *p, int who, struct rusage __user *ru)