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

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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>
This commit is contained in:
Andrea Righi 2025-03-25 10:32:12 +01:00 committed by Tejun Heo
parent a8897ed852
commit f0c6eab5e4
2 changed files with 6 additions and 6 deletions
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4
kernel/sched/ext.c
View File

@ -5361,6 +5361,8 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
*/
cpus_read_lock();
scx_idle_enable(ops);
if (scx_ops.init) {
ret = SCX_CALL_OP_RET(SCX_KF_UNLOCKED, init);
if (ret) {
@ -5427,8 +5429,6 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link)
if (scx_ops.cpu_acquire || scx_ops.cpu_release)
static_branch_enable(&scx_ops_cpu_preempt);
scx_idle_enable(ops);
/*
* Lock out forks, cgroup on/offlining and moves before opening the
* floodgate so that they don't wander into the operations prematurely.

8
kernel/sched/ext_idle.c
View File

@ -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);