linux-kernel - [PATCH v1 1/5] cpufreq: intel_pstate: Drop redundant locking from intel_pstate_driver

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Date: Thu, 21 Mar 2024 20:29:43 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Subject:
 [PATCH v1 1/5] cpufreq: intel_pstate: Drop redundant locking from
 intel_pstate_driver_cleanup()

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Remove the spinlock locking from intel_pstate_driver_cleanup() as it is
not necessary because no other code accessing all_cpu_data[] can run in
parallel with that function.

Had the locking been necessary, though, it would have been incorrect
because the lock in question is acquired from a hardirq handler and
it cannot be acquired from thread context without disabling interrupts.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/cpufreq/intel_pstate.c |    2 --
 1 file changed, 2 deletions(-)

Index: linux-pm/drivers/cpufreq/intel_pstate.c
===================================================================
--- linux-pm.orig/drivers/cpufreq/intel_pstate.c
+++ linux-pm/drivers/cpufreq/intel_pstate.c
@@ -3135,10 +3135,8 @@ static void intel_pstate_driver_cleanup(
 			if (intel_pstate_driver == &intel_pstate)
 				intel_pstate_clear_update_util_hook(cpu);

-			spin_lock(&hwp_notify_lock);
 			kfree(all_cpu_data[cpu]);
 			WRITE_ONCE(all_cpu_data[cpu], NULL);
-			spin_unlock(&hwp_notify_lock);
 		}
 	}
 	cpus_read_unlock();