docs: convert kref semaphore to mutex

Just converting this documentation semaphore reference, since we don't
want to promote semaphore usage.

Signed-off-by: Daniel Walker <dwalker@mvista.com>
Acked-by: Corey Minyard <minyard@acm.org>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/kref.txt b/Documentation/kref.txt
index f38b59d..130b6e8 100644 (file)
--- a/Documentation/kref.txt
+++ b/Documentation/kref.txt
@@ -141,10 +141,10 @@ 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 +155,12 @@ 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 +174,9 @@ 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 +191,13 @@ 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