[PATCH 3/4] docs: convert kref semaphore to mutex

Daniel Walker
2007-12-21T21:13:58Z

[-- Attachment #1: docs-kref-remove-semaphore-reference.patch --]
[-- Type: text/plain, Size: 2033 bytes --]

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

Signed-off-by: Daniel Walker <dwalker@mvista.com>

---
Documentation/kref.txt | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

Index: linux-2.6.23/Documentation/kref.txt
===================================================================
--- linux-2.6.23.orig/Documentation/kref.txt
+++ linux-2.6.23/Documentation/kref.txt
@@ -141,10 +141,10 @@ The last rule (rule 3) is the nastiest o
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 *r

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 *r

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

--