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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Lai Jiangshan <jiangshanlai+lkml@gmail.com>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>, Peter Oskolkov <posk@posk.io>,
        Tejun Heo <tj@kernel.org>, Jens Axboe <axboe@kernel.dk>
Subject: [PATCH v2] sched: Remove pointless preemption disable in
 sched_submit_work()
In-Reply-To: <CAJhGHyBwVLpcWoizJaMvQUFhAO_rz4CBQ1=D8hZ2iAadruh7WQ@mail.gmail.com>
References: <87sfxoai2l.ffs@tglx>
 <CAJhGHyBwVLpcWoizJaMvQUFhAO_rz4CBQ1=D8hZ2iAadruh7WQ@mail.gmail.com>
Date:   Wed, 29 Sep 2021 11:37:32 +0200
Message-ID: <8735pnafj7.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
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Neither wq_worker_sleeping() nor io_wq_worker_sleeping() require to be invoked
with preemption disabled:

  - The worker flag checks operations only need to be serialized against
    the worker thread itself.

  - The accounting and worker pool operations are serialized with locks.

which means that disabling preemption has neither a reason nor a
value. Remove it and update the stale comment.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
---
V2: Update comment as pointed out by Lai
---
 kernel/sched/core.c |   13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6319,20 +6319,14 @@ static inline void sched_submit_work(str
 
 	task_flags = tsk->flags;
 	/*
-	 * If a worker went to sleep, notify and ask workqueue whether
-	 * it wants to wake up a task to maintain concurrency.
-	 * As this function is called inside the schedule() context,
-	 * we disable preemption to avoid it calling schedule() again
-	 * in the possible wakeup of a kworker and because wq_worker_sleeping()
-	 * requires it.
+	 * If a worker goes to sleep, notify and ask workqueue whether it
+	 * wants to wake up a task to maintain concurrency.
 	 */
 	if (task_flags & (PF_WQ_WORKER | PF_IO_WORKER)) {
-		preempt_disable();
 		if (task_flags & PF_WQ_WORKER)
 			wq_worker_sleeping(tsk);
 		else
 			io_wq_worker_sleeping(tsk);
-		preempt_enable_no_resched();
 	}
 
 	if (tsk_is_pi_blocked(tsk))