Commit cb4ff914 authored May 14, 2025 by Tejun Heo

sched_ext: Explain the temporary situation around scx_root dereferences



Naked scx_root dereferences are being used as temporary markers to indicate
that they need to be updated to point to the right scheduler instance.
Explain the situation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Andrea Righi <arighi@nvidia.com>

parent a8433f7a

kernel/sched/ext.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -1016,6 +1016,14 @@ enum scx_ops_state {
		#define SCX_OPSS_STATE_MASK ((1LU << SCX_OPSS_QSEQ_SHIFT) - 1)
		#define SCX_OPSS_QSEQ_MASK (~SCX_OPSS_STATE_MASK)

		/*
		* NOTE: sched_ext is in the process of growing multiple scheduler support and
		* scx_root usage is in a transitional state. Naked dereferences are safe if the
		* caller is one of the tasks attached to SCX and explicit RCU dereference is
		* necessary otherwise. Naked scx_root dereferences trigger sparse warnings but
		* are used as temporary markers to indicate that the dereferences need to be
		* updated to point to the associated scheduler instances rather than scx_root.
		*/
		static struct scx_sched __rcu *scx_root;

		/*