Commit 6268d5bc authored Jan 09, 2025 by Changwoo Min Committed by Tejun Heo Jan 08, 2025

sched_ext: Replace rq_lock() to raw_spin_rq_lock() in scx_ops_bypass()



scx_ops_bypass() iterates all CPUs to re-enqueue all the scx tasks.
For each CPU, it acquires a lock using rq_lock() regardless of whether
a CPU is offline or the CPU is currently running a task in a higher
scheduler class (e.g., deadline). The rq_lock() is supposed to be used
for online CPUs, and the use of rq_lock() may trigger an unnecessary
warning in rq_pin_lock(). Therefore, replace rq_lock() to
raw_spin_rq_lock() in scx_ops_bypass().

Without this change, we observe the following warning:

===== START =====
[    6.615205] rq->balance_callback && rq->balance_callback != &balance_push_callback
[    6.615208] WARNING: CPU: 2 PID: 0 at kernel/sched/sched.h:1730 __schedule+0x1130/0x1c90
=====  END  =====

Fixes: 0e7ffff1 ("scx: Fix raciness in scx_ops_bypass()")
Signed-off-by: Changwoo Min <changwoo@igalia.com>
Acked-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

parent 30dd3b13

kernel/sched/ext.c

+6 −6

Original line number	Diff line number	Diff line
		@@ -4747,10 +4747,9 @@ static void scx_ops_bypass(bool bypass)
		*/
		for_each_possible_cpu(cpu) {
		struct rq *rq = cpu_rq(cpu);
		struct rq_flags rf;
		struct task_struct p, n;

		rq_lock(rq, &rf);
		raw_spin_rq_lock(rq);

		if (bypass) {
		WARN_ON_ONCE(rq->scx.flags & SCX_RQ_BYPASSING);
		@@ -4766,7 +4765,7 @@ static void scx_ops_bypass(bool bypass)
		* sees scx_rq_bypassing() before moving tasks to SCX.
		*/
		if (!scx_enabled()) {
		rq_unlock(rq, &rf);
		raw_spin_rq_unlock(rq);
		continue;
		}

		@@ -4786,10 +4785,11 @@ static void scx_ops_bypass(bool bypass)
		sched_enq_and_set_task(&ctx);
		}

		rq_unlock(rq, &rf);

		/* resched to restore ticks and idle state */
		resched_cpu(cpu);
		if (cpu_online(cpu) \|\| cpu == smp_processor_id())
		resched_curr(rq);

		raw_spin_rq_unlock(rq);
		}

		atomic_dec(&scx_ops_breather_depth);