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From:   David Vernet <void@manifault.com>
To:     linux-kernel@vger.kernel.org
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Subject: [PATCH v4 1/8] sched: Expose move_queued_task() from core.c
Date:   Mon, 11 Dec 2023 18:31:34 -0600
Message-ID: <20231212003141.216236-2-void@manifault.com>
In-Reply-To: <20231212003141.216236-1-void@manifault.com>
References: <20231212003141.216236-1-void@manifault.com>
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The migrate_task_to() function exposed from kernel/sched/core.c migrates
the current task, which is silently assumed to also be its first
argument, to the specified CPU. The function uses stop_one_cpu() to
migrate the task to the target CPU, which won't work if @p is not the
current task as the stop_one_cpu() callback isn't invoked on remote
CPUs.

While this operation is useful for task_numa_migrate() in fair.c, it
would be useful if move_queued_task() in core.c was given external
linkage, as it actually can be used to migrate any task to a CPU.

A follow-on patch will call move_queued_task() from fair.c when
migrating a task in a shared runqueue to a remote CPU.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: David Vernet <void@manifault.com>
---
 kernel/sched/core.c  | 4 ++--
 kernel/sched/sched.h | 3 +++
 2 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index db4be4921e7f..fb6f505d5792 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2518,8 +2518,8 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
  *
  * Returns (locked) new rq. Old rq's lock is released.
  */
-static struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
-				   struct task_struct *p, int new_cpu)
+struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
+			    struct task_struct *p, int new_cpu)
 {
 	lockdep_assert_rq_held(rq);
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index e58a54bda77d..5afdbd7e2381 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1787,6 +1787,9 @@ init_numa_balancing(unsigned long clone_flags, struct task_struct *p)
 
 #ifdef CONFIG_SMP
 
+
+extern struct rq *move_queued_task(struct rq *rq, struct rq_flags *rf,
+				   struct task_struct *p, int new_cpu);
 static inline void
 queue_balance_callback(struct rq *rq,
 		       struct balance_callback *head,
-- 
2.42.1