[PATCH] lock_cpu_hotplug only if CONFIG_CPU_HOTPLUG

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.

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 02579ec6b99cfc4e92d17394e6fcd57553e95466..5ecc291dc138ff291e83ae557c03a0c3bd5cd79d 100644 (file)
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -38,9 +38,6 @@ extern void unregister_cpu_notifier(struct notifier_block *nb);
 
 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_notifier(struct notifier_block *nb)
 {
 }
 
-#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 --git a/kernel/module.c b/kernel/module.c
index fc934874c881b1948c83b629ee8d0c7715fab58d..a51fa89ed1a17b4be01f7cfbcfd3dffef514c15a 100644 (file)
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -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 --git a/net/core/flow.c b/net/core/flow.c
index f13a1752b6032c27a423876e10300f3a3f143ef7..cef037afdf41230ae42cc0efae26b45a0abff8d7 100644 (file)
--- a/net/core/flow.c
+++ b/net/core/flow.c
@@ -283,10 +283,11 @@ static void flow_cache_flush_per_cpu(void *data)
 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();
 }