linux-kernel - [PATCH 02/46] sched_ext: Improve SCX_KF

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Message-ID: <20250920005931.2753828-3-tj@kernel.org>
Date: Fri, 19 Sep 2025 14:58:25 -1000
From: Tejun Heo <tj@...nel.org>
To: void@...ifault.com,
	arighi@...dia.com,
	multics69@...il.com
Cc: linux-kernel@...r.kernel.org,
	sched-ext@...ts.linux.dev,
	memxor@...il.com,
	bpf@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 02/46] sched_ext: Improve SCX_KF_DISPATCH comment

The comment for SCX_KF_DISPATCH was incomplete and didn't explain that
ops.dispatch() may temporarily release the rq lock, allowing ENQUEUE and
SELECT_CPU operations to be nested inside DISPATCH contexts.

Update the comment to clarify this nesting behavior and provide better
context for when these operations can occur within dispatch.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
 include/linux/sched/ext.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/ext.h b/include/linux/sched/ext.h
index 7047101dbf58..d82b7a9b0658 100644
--- a/include/linux/sched/ext.h
+++ b/include/linux/sched/ext.h
@@ -108,7 +108,11 @@ enum scx_kf_mask {
 	SCX_KF_UNLOCKED		= 0,	  /* sleepable and not rq locked */
 	/* ENQUEUE and DISPATCH may be nested inside CPU_RELEASE */
 	SCX_KF_CPU_RELEASE	= 1 << 0, /* ops.cpu_release() */
-	/* ops.dequeue (in REST) may be nested inside DISPATCH */
+	/*
+	 * ops.dispatch() may release rq lock temporarily and thus ENQUEUE and
+	 * SELECT_CPU may be nested inside. ops.dequeue (in REST) may also be
+	 * nested inside DISPATCH.
+	 */
 	SCX_KF_DISPATCH		= 1 << 1, /* ops.dispatch() */
 	SCX_KF_ENQUEUE		= 1 << 2, /* ops.enqueue() and ops.select_cpu() */
 	SCX_KF_SELECT_CPU	= 1 << 3, /* ops.select_cpu() */
-- 
2.51.0