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Date:   Thu, 28 Apr 2022 18:09:53 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     "Eric W. Biederman" <ebiederm@xmission.com>,
        linux-kernel@vger.kernel.org, rjw@rjwysocki.net, mingo@kernel.org,
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        rostedt@goodmis.org, mgorman@suse.de, bigeasy@linutronix.de,
        Will Deacon <will@kernel.org>, tj@kernel.org,
        linux-pm@vger.kernel.org, Richard Weinberger <richard@nod.at>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-um@lists.infradead.org, Chris Zankel <chris@zankel.net>,
        Max Filippov <jcmvbkbc@gmail.com>,
        inux-xtensa@linux-xtensa.org, Kees Cook <keescook@chromium.org>,
        Jann Horn <jannh@google.com>
Subject: Re: [PATCH 7/9] ptrace: Simplify the wait_task_inactive call in
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On Thu, Apr 28, 2022 at 04:57:50PM +0200, Oleg Nesterov wrote:

> > Shouldn't we then switch wait_task_inactive() so have & matching instead
> > of the current ==.
> 
> Sorry, I don't understand the context...

This.. I've always found it strange to have wti use a different matching
scheme from ttwu.

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f259621f4c93..c039aef4c8fe 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3304,7 +3304,7 @@ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state
 		 * is actually now running somewhere else!
 		 */
 		while (task_running(rq, p)) {
-			if (match_state && unlikely(READ_ONCE(p->__state) != match_state))
+			if (match_state && unlikely(!(READ_ONCE(p->__state) & match_state)))
 				return 0;
 			cpu_relax();
 		}
@@ -3319,7 +3319,7 @@ unsigned long wait_task_inactive(struct task_struct *p, unsigned int match_state
 		running = task_running(rq, p);
 		queued = task_on_rq_queued(p);
 		ncsw = 0;
-		if (!match_state || READ_ONCE(p->__state) == match_state)
+		if (!match_state || (READ_ONCE(p->__state) & match_state))
 			ncsw = p->nvcsw | LONG_MIN; /* sets MSB */
 		task_rq_unlock(rq, p, &rf);