[PATCH v2 08/14] sched_ext: Refactor lockup handlers into handle_lockup()

Tejun Heo
2025-11-10T20:56:46Z

scx_rcu_cpu_stall() and scx_softlockup() share the same pattern: check if the
scheduler is enabled under RCU read lock and trigger an error if so. Extract
the common pattern into handle_lockup() helper. Add scx_verror() macro and use
guard(rcu)().

This simplifies both handlers, reduces code duplication, and prepares for
hardlockup handling.

Cc: Dan Schatzberg <schatzberg.dan@gmail.com>
Cc: Emil Tsalapatis <etsal@meta.com>
Reviewed-by: Andrea Righi <arighi@nvidia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/sched/ext.c | 65 ++++++++++++++++++----------------------------
1 file changed, 25 insertions(+), 40 deletions(-)

diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
index 600918095245..d9572bf99b5b 100644
--- a/kernel/sched/ext.c
+++ b/kernel/sched/ext.c
@@ -192,6 +192,7 @@ static __printf(4, 5) bool scx_exit(struct scx_sched *sch,
}

#define scx_error(sch, fmt, args...) scx_exit((sch), SCX_EXIT_ERROR, 0, fmt, ##args)
+#define scx_verror(sch, fmt, args) scx_vexit((sch), SCX_EXIT_ERROR, 0, fmt, args)

#define SCX_HAS_OP(sch, op) test_bit(SCX_OP_IDX(op), (sch)->has_op)

@@ -3650,39 +3651,40 @@ bool scx_allow_ttwu_queue(const struct task_struct *p)
return false;
}

-/**
- * scx_rcu_cpu_stall - sched_ext RCU CPU stall handler
- *
- * While there are various reasons why RCU CPU stalls can occur on a system
- * that may not be caused by the current BPF scheduler, try kicking out the
- * current scheduler in an attempt to recover the system to a good state before
- * issuing panics.
- */
-bool scx_rcu_cpu_stall(void)
+static __printf(1, 2) bool handle_lockup(const char *fmt, ...)
{
struct scx_sched *sch;
+ va_list args;

- rcu_read_lock();
+ guard(rcu)();

sch = rcu_dereference(scx_root);
- if (unlikely(!sch)) {
- rcu_read_unlock();
+ if (unlikely(!sch))
return false;
- }

switch (scx_enable_state()) {
case SCX_ENABLING:
case SCX_ENABLED:
- break;
+ va_start(args, fmt);
+ scx_verror(sch, fmt, args);
+ va_end(args);
+ return true;
default:
- rcu_read_unlock();
return false;
}
+}

- scx_error(sch, "RCU CPU stall detected!");
- rcu_read_unlock();
-
- return true;
+/**
+ * scx_rcu_cpu_stall - sched_ext RCU CPU stall handler
+ *
+ * While there are various reasons why RCU CPU stalls can occur on a system
+ * that may not be caused by the current BPF scheduler, try kicking out the
+ * current scheduler in an attempt to recover the system to a good state before
+ * issuing panics.
+ */
+bool scx_rcu_cpu_stall(void)
+{
+ return handle_lockup("RCU CPU stall detected!");
}

/**
@@ -3697,28 +3699,11 @@ bool scx_rcu_cpu_stall(void)
*/
void scx_softlockup(u32 dur_s)
{
- struct scx_sched *sch;
-
- rcu_read_lock();
-
- sch = rcu_dereference(scx_root);
- if (unlikely(!sch))
- goto out_unlock;
-
- switch (scx_enable_state()) {
- case SCX_ENABLING:
- case SCX_ENABLED:
- break;
- default:
- goto out_unlock;
- }
-
- printk_deferred(KERN_ERR "sched_ext: Soft lockup - CPU%d stuck for %us, disabling \"%s\"\n",
- smp_processor_id(), dur_s, scx_root->ops.name);
+ if (!handle_lockup("soft lockup - CPU %d stuck for %us", smp_processor_id(), dur_s))
+ return;

- scx_error(sch, "soft lockup - CPU#%d stuck for %us", smp_processor_id(), dur_s);
-out_unlock:
- rcu_read_unlock();
+ printk_deferred(KERN_ERR "sched_ext: Soft lockup - CPU %d stuck for %us, disabling BPF scheduler\n",
+ smp_processor_id(), dur_s);
}

/**
--
2.51.2