ct_cpu_track_user() and the context_tracking_key static key are currently
restricted to boot-time use: the key is __ro_after_init and the function
is __init with __initdata state. This prevents enabling nohz_full context
tracking for CPUs isolated at runtime via cpuset partitions.
Split ct_cpu_track_user() into three functions:
ct_cpu_track_user(cpu) - sets per_cpu(context_tracking.active) and
increments context_tracking_key; callable
at runtime with the CPU offline.
ct_cpu_untrack_user(cpu) - reverses the above; for de-isolation.
ct_cpu_track_user_init(cpu) - __init wrapper; calls ct_cpu_track_user()
and handles TIF_NOHZ / tasklist setup.
Change context_tracking_key from DEFINE_STATIC_KEY_FALSE_RO to
DEFINE_STATIC_KEY_FALSE so that static_branch_inc/dec() can be called
after the __ro_after_init window closes.
Update tick_nohz_init() to call ct_cpu_track_user_init() so boot
behaviour is unchanged.
This is a prerequisite for DHM (Dynamic Housekeeping Management) runtime
CPU noise isolation without boot parameters.
Co-developed-by: Qiliang Yuan <[email protected]>
Signed-off-by: Qiliang Yuan <[email protected]>
Signed-off-by: Jing Wu <[email protected]>
---
include/linux/context_tracking.h | 2 ++
kernel/context_tracking.c | 38 ++++++++++++++++++++++++++++++++++----
kernel/time/tick-sched.c | 2 +-
3 files changed, 37 insertions(+), 5 deletions(-)
diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index af9fe87a09225..735d353d87560 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -12,6 +12,8 @@
#ifdef CONFIG_CONTEXT_TRACKING_USER
extern void ct_cpu_track_user(int cpu);
+extern void ct_cpu_untrack_user(int cpu);
+extern void __init ct_cpu_track_user_init(int cpu);
/* Called with interrupts disabled. */
extern void __ct_user_enter(enum ctx_state state);
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index a743e7ffa6c00..a81d9f8b85eed 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -411,7 +411,7 @@ static __always_inline void ct_kernel_enter(bool user, int
offset) { }
#define CREATE_TRACE_POINTS
#include <trace/events/context_tracking.h>
-DEFINE_STATIC_KEY_FALSE_RO(context_tracking_key);
+DEFINE_STATIC_KEY_FALSE(context_tracking_key);
EXPORT_SYMBOL_GPL(context_tracking_key);
static noinstr bool context_tracking_recursion_enter(void)
@@ -674,14 +674,44 @@ void user_exit_callable(void)
}
NOKPROBE_SYMBOL(user_exit_callable);
-void __init ct_cpu_track_user(int cpu)
+/**
+ * ct_cpu_track_user - enable context tracking for a CPU
+ * @cpu: target CPU (must be offline when called at runtime)
+ *
+ * Marks @cpu as actively tracking user/kernel transitions and increments
+ * the context_tracking_key refcount. Safe to call at runtime provided
+ * the CPU is offline so no context-tracking readers are active on it.
+ */
+void ct_cpu_track_user(int cpu)
{
- static __initdata bool initialized = false;
-
if (!per_cpu(context_tracking.active, cpu)) {
per_cpu(context_tracking.active, cpu) = true;
static_branch_inc(&context_tracking_key);
}
+}
+EXPORT_SYMBOL_GPL(ct_cpu_track_user);
+
+/**
+ * ct_cpu_untrack_user - disable context tracking for a CPU
+ * @cpu: target CPU (must be offline when called)
+ *
+ * Reverses ct_cpu_track_user(). The CPU must be offline so that no
+ * context-tracking readers are active on it.
+ */
+void ct_cpu_untrack_user(int cpu)
+{
+ if (per_cpu(context_tracking.active, cpu)) {
+ per_cpu(context_tracking.active, cpu) = false;
+ static_branch_dec(&context_tracking_key);
+ }
+}
+EXPORT_SYMBOL_GPL(ct_cpu_untrack_user);
+
+void __init ct_cpu_track_user_init(int cpu)
+{
+ static __initdata bool initialized = false;
+
+ ct_cpu_track_user(cpu);
if (initialized)
return;
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index cbbb87a0c6e7c..ba7adc671c580 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -677,7 +677,7 @@ void __init tick_nohz_init(void)
}
for_each_cpu(cpu, tick_nohz_full_mask)
- ct_cpu_track_user(cpu);
+ ct_cpu_track_user_init(cpu);
ret = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
"kernel/nohz:predown", NULL,
--
2.43.0
