mmc: s3c6410: enable ADMA feature in 6410 sdhci controller

[safe/jmp/linux-2.6] / Documentation / kref.txt

diff --git a/Documentation/kref.txt b/Documentation/kref.txt
index 96d8f56..ae203f9 100644 (file)
--- a/Documentation/kref.txt
+++ b/Documentation/kref.txt
@@ -67,7 +67,7 @@ void more_data_handling(void *cb_data)
        .
        . do stuff with data here
        .
-       kref_put(data, data_release);
+       kref_put(&data->refcount, data_release);
 }
 
 int my_data_handler(void)
@@ -84,7 +84,6 @@ int my_data_handler(void)
        task = kthread_run(more_data_handling, data, "more_data_handling");
        if (task == ERR_PTR(-ENOMEM)) {
                rv = -ENOMEM;
-               kref_put(&data->refcount, data_release);
                goto out;
        }
 
@@ -141,10 +140,10 @@ The last rule (rule 3) is the nastiest one to handle.  Say, for
 instance, you have a list of items that are each kref-ed, and you wish
 to get the first one.  You can't just pull the first item off the list
 and kref_get() it.  That violates rule 3 because you are not already
-holding a valid pointer.  You must add locks or semaphores.  For
-instance:
+holding a valid pointer.  You must add a mutex (or some other lock).
+For instance:
 
-static DECLARE_MUTEX(sem);
+static DEFINE_MUTEX(mutex);
 static LIST_HEAD(q);
 struct my_data
 {
@@ -155,12 +154,12 @@ struct my_data
 static struct my_data *get_entry()
 {
        struct my_data *entry = NULL;
-       down(&sem);
+       mutex_lock(&mutex);
        if (!list_empty(&q)) {
                entry = container_of(q.next, struct my_q_entry, link);
                kref_get(&entry->refcount);
        }
-       up(&sem);
+       mutex_unlock(&mutex);
        return entry;
 }
 
@@ -174,9 +173,9 @@ static void release_entry(struct kref *ref)
 
 static void put_entry(struct my_data *entry)
 {
-       down(&sem);
+       mutex_lock(&mutex);
        kref_put(&entry->refcount, release_entry);
-       up(&sem);
+       mutex_unlock(&mutex);
 }
 
 The kref_put() return value is useful if you do not want to hold the
@@ -191,13 +190,13 @@ static void release_entry(struct kref *ref)
 
 static void put_entry(struct my_data *entry)
 {
-       down(&sem);
+       mutex_lock(&mutex);
        if (kref_put(&entry->refcount, release_entry)) {
                list_del(&entry->link);
-               up(&sem);
+               mutex_unlock(&mutex);
                kfree(entry);
        } else
-               up(&sem);
+               mutex_unlock(&mutex);
 }
 
 This is really more useful if you have to call other routines as part
@@ -208,4 +207,9 @@ preferred as it is a little neater.
 
 Corey Minyard <minyard@acm.org>
 
-A lot of this was lifted from Greg KH's OLS presentation on krefs.
+A lot of this was lifted from Greg Kroah-Hartman's 2004 OLS paper and
+presentation on krefs, which can be found at:
+  http://www.kroah.com/linux/talks/ols_2004_kref_paper/Reprint-Kroah-Hartman-OLS2004.pdf
+and:
+  http://www.kroah.com/linux/talks/ols_2004_kref_talk/
+