[PATCH] sys_times: don't take tasklist_lock

sys_times: don't take tasklist_lock
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/sys.c

@@ -1206,7 +1206,7 @@ asmlinkage long sys_times(struct tms __user * tbuf)
 		struct task_struct *t;
 		cputime_t utime, stime, cutime, cstime;
 
-		read_lock(&tasklist_lock);
+		spin_lock_irq(&tsk->sighand->siglock);
 		utime = tsk->signal->utime;
 		stime = tsk->signal->stime;
 		t = tsk;
@@ -1216,20 +1216,9 @@ asmlinkage long sys_times(struct tms __user * tbuf)
 			t = next_thread(t);
 		} while (t != tsk);
 
-		/*
-		 * While we have tasklist_lock read-locked, no dying thread
-		 * can be updating current->signal->[us]time.  Instead,
-		 * we got their counts included in the live thread loop.
-		 * However, another thread can come in right now and
-		 * do a wait call that updates current->signal->c[us]time.
-		 * To make sure we always see that pair updated atomically,
-		 * we take the siglock around fetching them.
-		 */
-		spin_lock_irq(&tsk->sighand->siglock);
 		cutime = tsk->signal->cutime;
 		cstime = tsk->signal->cstime;
 		spin_unlock_irq(&tsk->sighand->siglock);
-		read_unlock(&tasklist_lock);
 
 		tmp.tms_utime = cputime_to_clock_t(utime);
 		tmp.tms_stime = cputime_to_clock_t(stime);