[PATCH 2/2] taskstats: add_del_listener() should ignore !valid listener's

[Oleg Nesterov <oleg@redhat.com>]

When send_cpu_listeners() finds the orphaned listener it marks
it as !valid and drops listeners->sem. Before it takes this sem
for wrinting, s->pid can be reused and add_del_listener() can
wrongly try to re-use this entry.

Change add_del_listener() to check ->valid = T.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---

 kernel/taskstats.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- ts/kernel/taskstats.c~2_ck_valid	2011-07-20 20:18:19.000000000 +0200
+++ ts/kernel/taskstats.c	2011-07-20 20:18:47.000000000 +0200
@@ -304,7 +304,7 @@ static int add_del_listener(pid_t pid, c
 			listeners = &per_cpu(listener_array, cpu);
 			down_write(&listeners->sem);
 			list_for_each_entry(s2, &listeners->list, list) {
-				if (s2->pid == pid)
+				if (s2->pid == pid && s2->valid)
 					goto exists;
 			}
 			list_add(&s->list, &listeners->list);