From b258298c70249e60ea7c65c60bd5ee1250609921 Mon Sep 17 00:00:00 2001
From: Pawel Dziepak <pdziepak@quarnos.org>
Date: Fri, 20 Dec 2013 01:31:32 +0100
Subject: [PATCH] kernel: Protect cpu_ent::active_time with sequential lock

atomic_{get, set}64() are problematic on architectures without 64 bit
compare and swap.
Also, using sequential lock instead of atomic access ensures that
any reads from cpu_ent::active_time won't require any writes to shared
memory.
---
 headers/private/kernel/cpu.h                  |  1 +
 src/system/kernel/cpu.cpp                     | 10 +++++++++-
 src/system/kernel/scheduler/scheduler_cpu.cpp |  5 ++++-
 src/system/kernel/smp.cpp                     |  1 +
 4 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/headers/private/kernel/cpu.h b/headers/private/kernel/cpu.h
index 17b056afdb..dad23c6c56 100644
--- a/headers/private/kernel/cpu.h
+++ b/headers/private/kernel/cpu.h
@@ -56,6 +56,7 @@ typedef struct cpu_ent {
 	timer			quantum_timer;
 
 	// keeping track of CPU activity
+	seqlock			active_time_lock;
 	bigtime_t		active_time;
 	bigtime_t		irq_time;
 	bigtime_t		interrupt_time;
diff --git a/src/system/kernel/cpu.cpp b/src/system/kernel/cpu.cpp
index a0ffcaf7f4..c984f353d1 100644
--- a/src/system/kernel/cpu.cpp
+++ b/src/system/kernel/cpu.cpp
@@ -159,7 +159,15 @@ cpu_get_active_time(int32 cpu)
 	if (cpu < 0 || cpu > smp_get_num_cpus())
 		return 0;
 
-	return atomic_get64(&gCPU[cpu].active_time);
+	bigtime_t activeTime;
+	uint32 count;
+
+	do {
+		count = acquire_read_seqlock(&gCPU[cpu].active_time_lock);
+		activeTime = gCPU[cpu].active_time;
+	} while (!release_read_seqlock(&gCPU[cpu].active_time_lock, count));
+
+	return activeTime;
 }
 
 
diff --git a/src/system/kernel/scheduler/scheduler_cpu.cpp b/src/system/kernel/scheduler/scheduler_cpu.cpp
index 3c8203ac12..57544ae83e 100644
--- a/src/system/kernel/scheduler/scheduler_cpu.cpp
+++ b/src/system/kernel/scheduler/scheduler_cpu.cpp
@@ -180,7 +180,10 @@ CPUEntry::TrackActivity(ThreadData* oldThreadData, ThreadData* nextThreadData)
 			= (oldThread->kernel_time - cpuEntry->last_kernel_time)
 				+ (oldThread->user_time - cpuEntry->last_user_time);
 
-		atomic_add64(&cpuEntry->active_time, active);
+		WriteSequentialLocker locker(cpuEntry->active_time_lock);
+		cpuEntry->active_time += active;
+		locker.Unlock();
+
 		oldThreadData->UpdateActivity(active);
 	}
 
diff --git a/src/system/kernel/smp.cpp b/src/system/kernel/smp.cpp
index 780912abc8..3631234771 100644
--- a/src/system/kernel/smp.cpp
+++ b/src/system/kernel/smp.cpp
@@ -701,6 +701,7 @@ acquire_read_seqlock(seqlock* lock) {
 
 bool
 release_read_seqlock(seqlock* lock, uint32 count) {
+	arch_cpu_memory_read_barrier();
 	uint32 current = atomic_get((int32*)&lock->count);
 
 	if (count % 2 == 1 || current != count) {