[Update][PATCH v1.2 4/5] cpufreq: intel_pstate: Get rid of unnecessary READ_ONCE() annotations

Rafael J. Wysocki
2024-03-28T19:00:43Z

Drop two redundant checks involving READ_ONCE() from notify_hwp_interrupt()
and make it check hwp_active without READ_ONCE() which is not necessary,
because that variable is only set once during the early initialization of
the driver.

In order to make that clear, annotate hwp_active with __ro_after_init.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---

v1.1 -> v1.2: Fix uninitialized memory access introduced in v1.1.

---
drivers/cpufreq/intel_pstate.c | 27 +++++----------------------
1 file changed, 5 insertions(+), 22 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -292,7 +292,7 @@ struct pstate_funcs {

static struct pstate_funcs pstate_funcs __read_mostly;

-static int hwp_active __read_mostly;
+static bool hwp_active __ro_after_init;
static int hwp_mode_bdw __read_mostly;
static bool per_cpu_limits __read_mostly;
static bool hwp_boost __read_mostly;
@@ -1636,11 +1636,10 @@ static cpumask_t hwp_intr_enable_mask;
void notify_hwp_interrupt(void)
{
unsigned int this_cpu = smp_processor_id();
- struct cpudata *cpudata;
unsigned long flags;
u64 value;

- if (!READ_ONCE(hwp_active) || !boot_cpu_has(X86_FEATURE_HWP_NOTIFY))
+ if (!hwp_active || !boot_cpu_has(X86_FEATURE_HWP_NOTIFY))
return;

rdmsrl_safe(MSR_HWP_STATUS, &value);
@@ -1652,24 +1651,8 @@ void notify_hwp_interrupt(void)
if (!cpumask_test_cpu(this_cpu, &hwp_intr_enable_mask))
goto ack_intr;

- /*
- * Currently we never free all_cpu_data. And we can't reach here
- * without this allocated. But for safety for future changes, added
- * check.
- */
- if (unlikely(!READ_ONCE(all_cpu_data)))
- goto ack_intr;
-
- /*
- * The free is done during cleanup, when cpufreq registry is failed.
- * We wouldn't be here if it fails on init or switch status. But for
- * future changes, added check.
- */
- cpudata = READ_ONCE(all_cpu_data[this_cpu]);
- if (unlikely(!cpudata))
- goto ack_intr;
-
- schedule_delayed_work(&cpudata->hwp_notify_work, msecs_to_jiffies(10));
+ schedule_delayed_work(&all_cpu_data[this_cpu]->hwp_notify_work,
+ msecs_to_jiffies(10));

spin_unlock_irqrestore(&hwp_notify_lock, flags);

@@ -3464,7 +3447,7 @@ static int __init intel_pstate_init(void
* deal with it.
*/
if ((!no_hwp && boot_cpu_has(X86_FEATURE_HWP_EPP)) || hwp_forced) {
- WRITE_ONCE(hwp_active, 1);
+ hwp_active = true;
hwp_mode_bdw = id->driver_data;
intel_pstate.attr = hwp_cpufreq_attrs;
intel_cpufreq.attr = hwp_cpufreq_attrs;