Commit 1373bed3 authored by Daniel Walker's avatar Daniel Walker Committed by Linus Torvalds

docs: convert kref semaphore to mutex

Just converting this documentation semaphore reference, since we don't
want to promote semaphore usage.
Signed-off-by: default avatarDaniel Walker <dwalker@mvista.com>
Acked-by: default avatarCorey Minyard <minyard@acm.org>
Cc: Greg KH <greg@kroah.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 13f14b4d
......@@ -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
......
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