[PATCH 13/31] wait_task_inactive: treat task->state and match_state as bitmasks

[Oleg Nesterov]

Change wait_task_inactive() to check "state & match_state" instead of
"state == match_state". This should not make any difference, but this
allows us to add more "stopped" bits which can be set or cleared
independently.

IOW. wait_task_inactive() assumes that if task->state != 0, it can
only be changed to TASK_RUNNING. Currently this is true, and in this
case "state & match_state" continues to work. But, unlike the current
check, it also works if task->state has other bits set while the caller
is only interested in, say, __TASK_TRACED.

Note: I think wait_task_inactive() should be cleanuped upstrean anyway,
nowadays we have TASK_WAKING and task->state != 0 doesn't necessarily
mean it is TASK_RUNNING. It also makes sense to exclude the !TASK_REPORT
bits during the check. Finally, probably this patch makes sense anyway
even without utrace. For example, a stopped _and_ traced thread could
have task->state = TASK_STOPPED | TASK_TRACED, this can be useful.

Signed-off-by: Oleg Nesterov <oleg(a)redhat.com&gt;
---
 kernel/sched.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index ccacdbd..66ef2fb 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2289,7 +2289,7 @@ unsigned long wait_task_inactive(struct task_struct *p, long
match_state)
 		 * is actually now running somewhere else!
 		 */
 		while (task_running(rq, p)) {
-			if (match_state && unlikely(p->state != match_state))
+			if (match_state && !likely(p->state & match_state))
 				return 0;
 			cpu_relax();
 		}
-- 
1.5.5.1