[PATCH 1/2] lock_cpu_hotplug only if CONFIG_CPU_HOTPLUG

From: Rusty Russell (rusty_at_rustcorp.com.au)
Date: 01/30/04

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    To: akpm@osdl.org
Date:	Fri, 30 Jan 2004 16:33:34 +1100

    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.

    Name: lock_cpu_hotplug/unlock_cpu_hotplug Macros only if CONFIG_HOTPLUG_CPU
    Author: Andrew Morton, Rusty Russell
    Status: Booted on 2.6.2-rc2-bk2
    Depends:

    D: The cpucontrol mutex is not required when no cpus can go up and down.
    D: Andrew wrote a wrapper for it to avoid #ifdefs, this expands that to
    D: only be defined for CONFIG_HOTPLUG_CPU, and uses it everywhere.
    D:
    D: The only downside is that the cpucontrol lock was overloaded by my
    D: recent patch to net/core/flow.c to protect it from reentrance, so
    D: this reintroduces the local flow_flush_sem. This code isn't speed
    D: critical, so taking two locks when CONFIG_HOTPLUG_CPU=y is not really
    D: an issue.

    diff -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .31749-linux-2.6.2-rc1-bk1/include/linux/cpu.h .31749-linux-2.6.2-rc1-bk1.updated/include/linux/cpu.h
    --- .31749-linux-2.6.2-rc1-bk1/include/linux/cpu.h 2004-01-25 01:25:08.000000000 +1100
    +++ .31749-linux-2.6.2-rc1-bk1.updated/include/linux/cpu.h 2004-01-25 01:25:46.000000000 +1100
    @@ -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 -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .31749-linux-2.6.2-rc1-bk1/kernel/module.c .31749-linux-2.6.2-rc1-bk1.updated/kernel/module.c
    --- .31749-linux-2.6.2-rc1-bk1/kernel/module.c 2004-01-21 16:19:08.000000000 +1100
    +++ .31749-linux-2.6.2-rc1-bk1.updated/kernel/module.c 2004-01-25 01:25:14.000000000 +1100
    @@ -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 -urpN --exclude TAGS -X /home/rusty/devel/kernel/kernel-patches/current-dontdiff --minimal .31749-linux-2.6.2-rc1-bk1/net/core/flow.c .31749-linux-2.6.2-rc1-bk1.updated/net/core/flow.c
    --- .31749-linux-2.6.2-rc1-bk1/net/core/flow.c 2004-01-25 01:25:08.000000000 +1100
    +++ .31749-linux-2.6.2-rc1-bk1.updated/net/core/flow.c 2004-01-25 01:25:14.000000000 +1100
    @@ -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();
     }
      

    --
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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