linux-kernel - Re: [PATCH -tip 22/32] sched: Split the cookie and setup per-task cookie on fork

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Message-ID: <20201201185253.GA215200@google.com>
Date:   Tue, 1 Dec 2020 13:52:53 -0500
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        torvalds@...ux-foundation.org, fweisbec@...il.com,
        keescook@...omium.org, kerrnel@...gle.com,
        Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org,
        Chen Yu <yu.c.chen@...el.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Agata Gruza <agata.gruza@...el.com>,
        Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
        graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
        pjt@...gle.com, rostedt@...dmis.org, derkling@...gle.com,
        benbjiang@...cent.com,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        James.Bottomley@...senpartnership.com, OWeisse@...ch.edu,
        Dhaval Giani <dhaval.giani@...cle.com>,
        Junaid Shahid <junaids@...gle.com>, jsbarnes@...gle.com,
        chris.hyser@...cle.com, Ben Segall <bsegall@...gle.com>,
        Josh Don <joshdon@...gle.com>, Hao Luo <haoluo@...gle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Tim Chen <tim.c.chen@...el.com>
Subject: Re: [PATCH -tip 22/32] sched: Split the cookie and setup per-task
 cookie on fork

On Wed, Nov 25, 2020 at 02:03:22PM +0100, Peter Zijlstra wrote:
> On Tue, Nov 17, 2020 at 06:19:52PM -0500, Joel Fernandes (Google) wrote:
> > +static bool sched_core_get_task_cookie(unsigned long cookie)
> > +{
> > +	struct sched_core_cookie *ptr = (struct sched_core_cookie *)cookie;
> > +
> > +	/*
> > +	 * NOTE: sched_core_put() is not done by put_task_cookie(). Instead, it
> > +	 * is done after the stopper runs.
> > +	 */
> > +	sched_core_get();
> > +	return refcount_inc_not_zero(&ptr->refcnt);
> 
> See below, but afaict this should be refcount_inc().

Fully agreed with all these. Updated with diff as below. Will test further
and post next version soon. Thanks!

---8<-----------------------

diff --git a/kernel/sched/coretag.c b/kernel/sched/coretag.c
index 2fb5544a4a18..8fce3f4b7cae 100644
--- a/kernel/sched/coretag.c
+++ b/kernel/sched/coretag.c
@@ -288,12 +288,12 @@ static unsigned long sched_core_alloc_task_cookie(void)
 	return (unsigned long)ck;
 }
 
-static bool sched_core_get_task_cookie(unsigned long cookie)
+static void sched_core_get_task_cookie(unsigned long cookie)
 {
 	struct sched_core_task_cookie *ptr =
 		(struct sched_core_task_cookie *)cookie;
 
-	return refcount_inc_not_zero(&ptr->refcnt);
+	refcount_inc(&ptr->refcnt);
 }
 
 static void sched_core_put_task_cookie(unsigned long cookie)
@@ -392,10 +392,7 @@ int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2)
 		sched_core_get(); /* For the alloc. */
 
 		/* Add another reference for the other task. */
-		if (!sched_core_get_task_cookie(cookie)) {
-			ret = -EINVAL;
-			goto out_unlock;
-		}
+		sched_core_get_task_cookie(cookie);
 		sched_core_get(); /* For the other task. */
 
 		wr.tasks[0] = t1;
@@ -411,10 +408,7 @@ int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2)
 
 	} else if (!t1->core_task_cookie && t2->core_task_cookie) {
 		/* CASE 3. */
-		if (!sched_core_get_task_cookie(t2->core_task_cookie)) {
-			ret = -EINVAL;
-			goto out_unlock;
-		}
+		sched_core_get_task_cookie(t2->core_task_cookie);
 		sched_core_get();
 
 		wr.tasks[0] = t1;
@@ -422,10 +416,7 @@ int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2)
 
 	} else {
 		/* CASE 4. */
-		if (!sched_core_get_task_cookie(t2->core_task_cookie)) {
-			ret = -EINVAL;
-			goto out_unlock;
-		}
+		sched_core_get_task_cookie(t2->core_task_cookie);
 		sched_core_get();
 
 		sched_core_put_task_cookie(t1->core_task_cookie);
-- 
2.29.2.454.gaff20da3a2-goog