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Thu, 15 Oct 2026 01:29:26 -0700 (PDT) Received: from lima-kdev.local ([85.100.66.184]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48defca4013sm7369761f8f.9.2026.10.15.01.29.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 15 Oct 2026 01:29:26 -0700 (PDT) From: Kayra Cizmeci To: peterz@infradead.org, Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Kayra Cizmeci Cc: christian.loehle@arm.com, linux-kernel@vger.kernel.org Subject: [PATCH] Revert "sched/fair: Remove dead code on enqueue_task_fair()" Date: Thu, 15 Oct 2026 11:29:18 +0300 Message-ID: <20261015082919.4344-1-kayracizmeci@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit This reverts commit 819224e506bc7c2d61ec6a58ec6e876b505abce9. The cfs_rq->curr == se case can actually happen with CFS_BANDWIDTH, so the removed code is needed. Document this. Fixes: 819224e506bc ("sched/fair: Remove dead code on enqueue_task_fair()") Reported-by: Christian Loehle Link: https://lore.kernel.org/lkml/fd3f9d83-cb5b-496b-b7c1-b40f31cf795e@arm.com/ Signed-off-by: Kayra Cizmeci --- Killing my own beast :-). Not tested at all BTW. kernel/sched/fair.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index b42a0ca2a69e..436270f1786a 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -7991,6 +7991,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) struct sched_entity *se = &p->se; struct cfs_rq *cfs_rq = &rq->cfs; unsigned long weight; + bool curr; if (task_is_throttled(p) && enqueue_throttled_task(p)) return; @@ -8019,14 +8020,25 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags) if (p->in_iowait) cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT); + curr = (cfs_rq->curr == se); + /* + * This can actually happen with CFS_BANDWIDTH, a task can be throttled + * and dequeued, unthrottled from another CPU and then enqueued again + * before schedule(). + */ + if (curr) + place_entity(cfs_rq, se, flags); if (se->on_rq && se->sched_delayed) requeue_delayed_entity(cfs_rq, se); weight = enqueue_hierarchy(p, flags); - reweight_eevdf(cfs_rq, se, weight, false); - place_entity(cfs_rq, se, flags | ENQUEUE_QUEUED); - __enqueue_entity(cfs_rq, se); + + if (!curr) { + reweight_eevdf(cfs_rq, se, weight, false); + place_entity(cfs_rq, se, flags | ENQUEUE_QUEUED); + __enqueue_entity(cfs_rq, se); + } if (!rq_h_nr_queued && rq->cfs.h_nr_queued) dl_server_start(&rq->fair_server); -- 2.53.0