From: Rusty Russell <rusty@rustcorp.com.au>
The cpucontrol mutex is not required when no cpus can go up and down.
Andrew wrote a wrapper for it to avoid #ifdefs, this expands that to only
be defined for CONFIG_HOTPLUG_CPU, and uses it everywhere.
The only downside is that the cpucontrol lock was overloaded by my recent
patch to net/core/flow.c to protect it from reentrance, so this
reintroduces the local flow_flush_sem. This code isn't speed critical, so
taking two locks when CONFIG_HOTPLUG_CPU=y is not really an issue.
---
include/linux/cpu.h | 14 ++++++++------
kernel/module.c | 6 +++---
net/core/flow.c | 6 ++++--
3 files changed, 15 insertions(+), 11 deletions(-)
diff -puN include/linux/cpu.h~lock_cpu_hotplug-fixes include/linux/cpu.h
--- 25/include/linux/cpu.h~lock_cpu_hotplug-fixes 2004-01-29 22:30:27.000000000 -0800
+++ 25-akpm/include/linux/cpu.h 2004-01-29 22:30:27.000000000 -0800
@@ -38,9 +38,6 @@ extern void unregister_cpu_notifier(stru
int cpu_up(unsigned int cpu);
-#define lock_cpu_hotplug() down(&cpucontrol)
-#define unlock_cpu_hotplug() up(&cpucontrol)
-
#else
static inline int register_cpu_notifier(struct notifier_block *nb)
@@ -51,12 +48,17 @@ static inline void unregister_cpu_notifi
{
}
-#define lock_cpu_hotplug() do { } while (0)
-#define unlock_cpu_hotplug() do { } while (0)
-
#endif /* CONFIG_SMP */
extern struct sysdev_class cpu_sysdev_class;
+#ifdef CONFIG_HOTPLUG_CPU
/* Stop CPUs going up and down. */
extern struct semaphore cpucontrol;
+#define lock_cpu_hotplug() down(&cpucontrol)
+#define unlock_cpu_hotplug() up(&cpucontrol)
+#else
+#define lock_cpu_hotplug() do { } while (0)
+#define unlock_cpu_hotplug() do { } while (0)
+#endif
+
#endif /* _LINUX_CPU_H_ */
diff -puN kernel/module.c~lock_cpu_hotplug-fixes kernel/module.c
--- 25/kernel/module.c~lock_cpu_hotplug-fixes 2004-01-29 22:30:27.000000000 -0800
+++ 25-akpm/kernel/module.c 2004-01-29 22:30:27.000000000 -0800
@@ -554,7 +554,7 @@ static int stop_refcounts(void)
stopref_state = STOPREF_WAIT;
/* No CPUs can come up or down during this. */
- down(&cpucontrol);
+ lock_cpu_hotplug();
for (i = 0; i < NR_CPUS; i++) {
if (i == cpu || !cpu_online(i))
@@ -572,7 +572,7 @@ static int stop_refcounts(void)
/* If some failed, kill them all. */
if (ret < 0) {
stopref_set_state(STOPREF_EXIT, 1);
- up(&cpucontrol);
+ unlock_cpu_hotplug();
return ret;
}
@@ -595,7 +595,7 @@ static void restart_refcounts(void)
stopref_set_state(STOPREF_EXIT, 0);
local_irq_enable();
preempt_enable();
- up(&cpucontrol);
+ unlock_cpu_hotplug();
}
#else /* ...!SMP */
static inline int stop_refcounts(void)
diff -puN net/core/flow.c~lock_cpu_hotplug-fixes net/core/flow.c
--- 25/net/core/flow.c~lock_cpu_hotplug-fixes 2004-01-29 22:30:27.000000000 -0800
+++ 25-akpm/net/core/flow.c 2004-01-29 22:30:27.000000000 -0800
@@ -283,10 +283,11 @@ static void flow_cache_flush_per_cpu(voi
void flow_cache_flush(void)
{
struct flow_flush_info info;
+ static DECLARE_MUTEX(flow_flush_sem);
- /* Don't want cpus going down or up during this, also protects
- * against multiple callers. */
+ /* Don't want cpus going down or up during this. */
lock_cpu_hotplug();
+ down(&flow_flush_sem);
atomic_set(&info.cpuleft, num_online_cpus());
init_completion(&info.completion);
@@ -296,6 +297,7 @@ void flow_cache_flush(void)
local_bh_enable();
wait_for_completion(&info.completion);
+ up(&flow_flush_sem);
unlock_cpu_hotplug();
}
_