sched_ext: initialize built-in idle state before ops.init()

A BPF scheduler may want to use the built-in idle cpumasks in ops.init()
before the scheduler is fully initialized, either directly or through a
BPF timer for example.

However, this would result in an error, since the idle state has not
been properly initialized yet.

This can be easily verified by modifying scx_simple to call
scx_bpf_get_idle_cpumask() in ops.init():

$ sudo scx_simple

DEBUG DUMP
===========================================================================

scx_simple[121] triggered exit kind 1024:
  runtime error (built-in idle tracking is disabled)
...

Fix this by properly initializing the idle state before ops.init() is
called. With this change applied:

$ sudo scx_simple
local=2 global=0
local=19 global=11
local=23 global=11
...

Fixes: d73249f88743d ("sched_ext: idle: Make idle static keys private")
Signed-off-by: Andrea Righi <arighi@nvidia.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 4 insertions, 4 deletions

diff --git a/kernel/sched/ext_idle.c b/kernel/sched/ext_idle.c
index b5f451e616d4..cb343ca889e0 100644
--- a/kernel/sched/ext_idle.c
+++ b/kernel/sched/ext_idle.c
@@ -721,14 +721,14 @@ static void reset_idle_masks(struct sched_ext_ops *ops)
 void scx_idle_enable(struct sched_ext_ops *ops)
 {
 	if (!ops->update_idle || (ops->flags & SCX_OPS_KEEP_BUILTIN_IDLE))
-		static_branch_enable(&scx_builtin_idle_enabled);
+		static_branch_enable_cpuslocked(&scx_builtin_idle_enabled);
 	else
-		static_branch_disable(&scx_builtin_idle_enabled);
+		static_branch_disable_cpuslocked(&scx_builtin_idle_enabled);
 
 	if (ops->flags & SCX_OPS_BUILTIN_IDLE_PER_NODE)
-		static_branch_enable(&scx_builtin_idle_per_node);
+		static_branch_enable_cpuslocked(&scx_builtin_idle_per_node);
 	else
-		static_branch_disable(&scx_builtin_idle_per_node);
+		static_branch_disable_cpuslocked(&scx_builtin_idle_per_node);
 
 #ifdef CONFIG_SMP
 	reset_idle_masks(ops);