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From:   Liangyan <liangyan.peng@linux.alibaba.com>
To:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org
Cc:     shanpeic@linux.alibaba.com, xlpang@linux.alibaba.com
Subject: [PATCH] sched/fair: don't assign runtime for throttled cfs_rq
Date:   Thu, 15 Aug 2019 02:00:21 +0800
Message-Id: <20190814180021.165389-1-liangyan.peng@linux.alibaba.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

do_sched_cfs_period_timer() will refill cfs_b runtime and call
distribute_cfs_runtime() to unthrottle cfs_rq, sometimes cfs_b->runtime
will allocate all quota to one cfs_rq incorrectly.
This will cause other cfs_rq can't get runtime and will be throttled.
We find that one throttled cfs_rq has non-negative
cfs_rq->runtime_remaining and cause an unexpetced cast from s64 to u64
in snippet: distribute_cfs_runtime() {
runtime = -cfs_rq->runtime_remaining + 1; }.
This cast will cause that runtime will be a large number and
cfs_b->runtime will be subtracted to be zero at last.

This commit prevents cfs_rq to be assgined new runtime if it has been
throttled to avoid the above incorrect type cast.

Signed-off-by: Liangyan <liangyan.peng@linux.alibaba.com>
---
 kernel/sched/fair.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 81fd8a2a605b..b14d67d28138 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -4068,6 +4068,8 @@ static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
 	if (likely(cfs_rq->runtime_remaining > 0))
 		return;
 
+	if (cfs_rq->throttled)
+		return;
 	/*
 	 * if we're unable to extend our runtime we resched so that the active
 	 * hierarchy can be throttled
-- 
2.14.4.44.g2045bb6