linux2.6.28.1编译时__mutex_unlock_slowpath未定义的错误

http://blog.chinaunix.net/uid-9688646-id-3413844.html
下午在编译2.6.28.1内核的时候，采用的是默认的x86_config的配置，make bzImage的时候报错，提示：

    undefined reference to __mutex_unlock_slowpath，

  上网搜索半天也得不到有用的结果，只好自己想办法了。首先索引内核源代码，看下__mutex_unlock_slowpath到底是何方神圣。在http://lxr.linux.no/linux/中得到的结果如下：

  

268/*
269 * Release the lock, slowpath:
270 */
271static noinline void
272__mutex_unlock_slowpath(atomic_t *lock_count)
273{
274        __mutex_unlock_common_slowpath(lock_count, 1);
275}
276

  没发现任何问题，很明显代码中是存在了定义的。那为什么还是说找不到呢？只可能相关的宏定义没有打开的原因。继续搜索：

5#ifndef CONFIG_DEBUG_LOCK_ALLOC
  56/*
  57 * We split the mutex lock/unlock logic into separate fastpath and
  58 * slowpath functions, to reduce the register pressure on the fastpath.
  59 * We also put the fastpath first in the kernel image, to make sure the
  60 * branch is predicted by the CPU as default-untaken.
  61 */
  62static void noinline __sched
  63__mutex_lock_slowpath(atomic_t *lock_count);
  64
  65/***
  66 * mutex_lock - acquire the mutex
  67 * @lock: the mutex to be acquired
  68 *
  69 * Lock the mutex exclusively for this task. If the mutex is not
  70 * available right now, it will sleep until it can get it.
  71 *
  72 * The mutex must later on be released by the same task that
  73 * acquired it. Recursive locking is not allowed. The task
  74 * may not exit without first unlocking the mutex. Also, kernel
  75 * memory where the mutex resides mutex must not be freed with
  76 * the mutex still locked. The mutex must first be initialized
  77 * (or statically defined) before it can be locked. memset()-ing
  78 * the mutex to 0 is not allowed.
  79 *
  80 * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
  81 *   checks that will enforce the restrictions and will also do
  82 *   deadlock debugging. )
  83 *
  84 * This function is similar to (but not equivalent to) down().
  85 */
  86void inline __sched mutex_lock(struct mutex *lock)
  87{
  88        might_sleep();
  89        /*
  90         * The locking fastpath is the 1->0 transition from
  91         * 'unlocked' into 'locked' state.
  92         */
  93        __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
  94}
  95
  96EXPORT_SYMBOL(mutex_lock);
  97#endif
  98
  99static noinline void __sched __mutex_unlock_slowpath(atomic_t *lock_count);
 100
 101/***
 102 * mutex_unlock - release the mutex
 103 * @lock: the mutex to be released
 104 *
 105 * Unlock a mutex that has been locked by this task previously.
 106 *
 107 * This function must not be used in interrupt context. Unlocking
 108 * of a not locked mutex is not allowed.
 109 *
 110 * This function is similar to (but not equivalent to) up().
 111 */
 112void __sched mutex_unlock(struct mutex *lock)
 113{
 114        /*
 115         * The unlocking fastpath is the 0->1 transition from 'locked'
 116         * into 'unlocked' state:
 117         */
 118        __mutex_fastpath_unlock(&lock->count, __mutex_unlock_slowpath);
 119}
 120

   发现CONFIG_DEBUG_LOCK_ALLOC控制了__mutex_unlock_slowpath的定义。打开.config搜索，看是否CONFIG_DEBUG_LOCK_ALLOC宏是否设置，发现设置了。那肯定还有另外的宏在起控制作用。继续搜索，发现如下结果：

    

22/*
23 * In the DEBUG case we are using the "NULL fastpath" for mutexes,
24 * which forces all calls into the slowpath:
25 */
26#ifdef CONFIG_DEBUG_MUTEXES
27# include "mutex-debug.h"
28# include
29#else
30# include "mutex.h"
31# include
32#endif
33

   可以看到CONFIG_DEBUG_MUTEXES控制了头文件的包含关系，再次在.config中搜索，发现CONFIG_DEBUG_MUTEXES宏果然没有定义。将其改成y，重新编译，通过。