[PATCH 7.2.y 1/2] sched_ext: Generalize local-DSQ handling to rq-owned DSQs

[Sasha Levin <sashal@kernel.org>]

From: Tejun Heo <tj@kernel.org>

[ Upstream commit bf6cf1886a56eaf929d8193a3f4b30be59a778e2 ]

The local DSQ is synchronized by the containing rq lock rather than its own
dsq->lock. A later patch adds a second such DSQ. In preparation, factor the
"rq owns the lock" test into dsq_is_rq_owned() and rename
local_dsq_post_enq() to rq_owned_post_enq(), taking @rq explicitly.

No behavior change.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Stable-dep-of: 7de9a6fb44ea ("sched_ext: Wait for SCX_OPSS_DISPATCHING before reenqueueing a task")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/sched/ext/ext.c | 34 ++++++++++++++++++++++------------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/ext/ext.c b/kernel/sched/ext/ext.c
index 906e4f08967f8..665825f1d1ff4 100644
--- a/kernel/sched/ext/ext.c
+++ b/kernel/sched/ext/ext.c
@@ -95,6 +95,17 @@ static atomic_long_t scx_hotplug_seq = ATOMIC_LONG_INIT(0);
 /* Global cursor for the per-CPU tid allocator. Starts at 1; tid 0 is reserved. */
 static atomic64_t scx_tid_cursor = ATOMIC64_INIT(1);
 
+/* is @dsq synchronized by the containing rq lock instead of dsq->lock? */
+static bool dsq_is_rq_owned(struct scx_dispatch_q *dsq)
+{
+	switch (dsq->id) {
+	case SCX_DSQ_LOCAL:
+		return true;
+	default:
+		return false;
+	}
+}
+
 #ifdef CONFIG_EXT_SUB_SCHED
 /*
  * The sub sched being enabled. Used by scx_disable_and_exit_task() to exit
@@ -1466,11 +1477,10 @@ static void call_task_dequeue(struct scx_sched *sch, struct rq *rq,
 	p->scx.flags &= ~SCX_TASK_IN_CUSTODY;
 }
 
-static void local_dsq_post_enq(struct scx_sched *sch, struct scx_dispatch_q *dsq,
-			       struct task_struct *p, u64 enq_flags)
+static void rq_owned_post_enq(struct scx_sched *sch, struct rq *rq,
+			      struct scx_dispatch_q *dsq, struct task_struct *p,
+			      u64 enq_flags)
 {
-	struct rq *rq = container_of(dsq, struct rq, scx.local_dsq);
-
 	call_task_dequeue(sch, rq, p, 0);
 
 	/*
@@ -1530,13 +1540,13 @@ static void dispatch_enqueue(struct scx_sched *sch, struct rq *rq,
 			     struct scx_dispatch_q *dsq, struct task_struct *p,
 			     u64 enq_flags)
 {
-	bool is_local = dsq->id == SCX_DSQ_LOCAL;
+	bool is_rq_owned = dsq_is_rq_owned(dsq);
 
 	WARN_ON_ONCE(p->scx.dsq || !list_empty(&p->scx.dsq_list.node));
 	WARN_ON_ONCE((p->scx.dsq_flags & SCX_TASK_DSQ_ON_PRIQ) ||
 		     !RB_EMPTY_NODE(&p->scx.dsq_priq));
 
-	if (!is_local) {
+	if (!is_rq_owned) {
 		raw_spin_lock_nested(&dsq->lock,
 			(enq_flags & SCX_ENQ_NESTED) ? SINGLE_DEPTH_NESTING : 0);
 
@@ -1631,8 +1641,8 @@ static void dispatch_enqueue(struct scx_sched *sch, struct rq *rq,
 	 * ops_state first, both sides would modify p->scx.flags
 	 * concurrently in a non-atomic way.
 	 */
-	if (is_local) {
-		local_dsq_post_enq(sch, dsq, p, enq_flags);
+	if (is_rq_owned) {
+		rq_owned_post_enq(sch, rq, dsq, p, enq_flags);
 	} else {
 		/*
 		 * Task on global/bypass DSQ: leave custody, task on
@@ -1679,7 +1689,7 @@ static void task_unlink_from_dsq(struct task_struct *p,
 static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
 {
 	struct scx_dispatch_q *dsq = p->scx.dsq;
-	bool is_local = dsq == &rq->scx.local_dsq;
+	bool is_rq_owned = dsq && dsq_is_rq_owned(dsq);
 
 	lockdep_assert_rq_held(rq);
 
@@ -1703,7 +1713,7 @@ static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
 		return;
 	}
 
-	if (!is_local)
+	if (!is_rq_owned)
 		raw_spin_lock(&dsq->lock);
 
 	/*
@@ -1725,7 +1735,7 @@ static void dispatch_dequeue(struct rq *rq, struct task_struct *p)
 	}
 	p->scx.dsq = NULL;
 
-	if (!is_local)
+	if (!is_rq_owned)
 		raw_spin_unlock(&dsq->lock);
 }
 
@@ -2277,7 +2287,7 @@ static void move_local_task_to_local_dsq(struct scx_sched *sch,
 	dsq_inc_nr(dst_dsq, p, enq_flags);
 	p->scx.dsq = dst_dsq;
 
-	local_dsq_post_enq(sch, dst_dsq, p, enq_flags);
+	rq_owned_post_enq(sch, dst_rq, dst_dsq, p, enq_flags);
 }
 
 /**
-- 
2.53.0