linux-kernel - Re: [PATCH 1/2] sched: eliminate bandwidth race between throttling and distribution

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Message-ID: <20200414105220.GL20713@hirez.programming.kicks-ass.net>
Date:   Tue, 14 Apr 2020 12:52:20 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Don <joshdon@...gle.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Paul Turner <pjt@...gle.com>,
        Huaixin Chang <changhuaixin@...ux.alibaba.com>,
        Phil Auld <pauld@...head.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] sched: eliminate bandwidth race between throttling
 and distribution

On Fri, Apr 10, 2020 at 03:52:07PM -0700, Josh Don wrote:

> -/* returns 0 on failure to allocate runtime */
> +/* returns 0 on failure to allocate runtime, called with cfs_b->lock held */

That's a gross mis-spelling of lockdep_assert_held(); and since I was
editing things anyway it now looks like so:

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4587,11 +4587,13 @@ static inline struct cfs_bandwidth *tg_c
 	return &tg->cfs_bandwidth;
 }
 
-/* returns 0 on failure to allocate runtime, called with cfs_b->lock held */
+/* returns 0 on failure to allocate runtime */
 static int __assign_cfs_rq_runtime(struct cfs_bandwidth *cfs_b,
 				   struct cfs_rq *cfs_rq, u64 target_runtime)
 {
-	u64 amount = 0, min_amount;
+	u64 min_amount, amount = 0;
+
+	lockdep_assert_held(cfs_rq->lock);
 
 	/* note: this is a positive sum as runtime_remaining <= 0 */
 	min_amount = target_runtime - cfs_rq->runtime_remaining;
@@ -4616,12 +4618,11 @@ static int __assign_cfs_rq_runtime(struc
 /* returns 0 on failure to allocate runtime */
 static int assign_cfs_rq_runtime(struct cfs_rq *cfs_rq)
 {
-	int ret;
 	struct cfs_bandwidth *cfs_b = tg_cfs_bandwidth(cfs_rq->tg);
+	int ret;
 
 	raw_spin_lock(&cfs_b->lock);
-	ret = __assign_cfs_rq_runtime(cfs_b, cfs_rq,
-				      sched_cfs_bandwidth_slice());
+	ret = __assign_cfs_rq_runtime(cfs_b, cfs_rq, sched_cfs_bandwidth_slice());
 	raw_spin_unlock(&cfs_b->lock);
 
 	return ret;