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once: make helper generic for calling functions once

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Make the get_random_once() helper generic enough, so that functions
in general would only be called once, where one user of this is then
net_get_random_once().

The only implementation specific call is to get_random_bytes(), all
the rest of this *_once() facility would be duplicated among different
subsystems otherwise. The new DO_ONCE() helper will be used by prandom()
later on, but might also be useful for other scenarios/subsystems as
well where a one-time initialization in often-called, possibly fast
path code could occur.

Signed-off-by: Hannes Frederic Sowa <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Acked-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
This commit is contained in:
Hannes Frederic Sowa 2015-10-08 01:20:36 +02:00 • committed by David S. Miller
commit c90aeb9482
2 changed files with 76 additions and 35 deletions
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50
lib/once.c
View file

@ -3,52 +3,60 @@
#include <linux/once.h>
#include <linux/random.h>
struct __random_once_work {
struct once_work {
struct work_struct work;
struct static_key *key;
};
static void __random_once_deferred(struct work_struct *w)
static void once_deferred(struct work_struct *w)
{
struct __random_once_work *work;
struct once_work *work;
work = container_of(w, struct __random_once_work, work);
work = container_of(w, struct once_work, work);
BUG_ON(!static_key_enabled(work->key));
static_key_slow_dec(work->key);
kfree(work);
}
static void __random_once_disable_jump(struct static_key *key)
static void once_disable_jump(struct static_key *key)
{
struct __random_once_work *w;
struct once_work *w;
w = kmalloc(sizeof(*w), GFP_ATOMIC);
if (!w)
return;
INIT_WORK(&w->work, __random_once_deferred);
INIT_WORK(&w->work, once_deferred);
w->key = key;
schedule_work(&w->work);
}
bool __get_random_once(void *buf, int nbytes, bool *done,
struct static_key *once_key)
{
static DEFINE_SPINLOCK(lock);
unsigned long flags;
static DEFINE_SPINLOCK(once_lock);
spin_lock_irqsave(&lock, flags);
bool __do_once_start(bool *done, unsigned long *flags)
__acquires(once_lock)
{
spin_lock_irqsave(&once_lock, *flags);
if (*done) {
spin_unlock_irqrestore(&lock, flags);
spin_unlock_irqrestore(&once_lock, *flags);
/* Keep sparse happy by restoring an even lock count on
* this lock. In case we return here, we don't call into
* __do_once_done but return early in the DO_ONCE() macro.
*/
__acquire(once_lock);
return false;
}
get_random_bytes(buf, nbytes);
*done = true;
spin_unlock_irqrestore(&lock, flags);
__random_once_disable_jump(once_key);
return true;
}
EXPORT_SYMBOL(__get_random_once);
EXPORT_SYMBOL(__do_once_start);
void __do_once_done(bool *done, struct static_key *once_key,
unsigned long *flags)
__releases(once_lock)
{
*done = true;
spin_unlock_irqrestore(&once_lock, *flags);
once_disable_jump(once_key);
}
EXPORT_SYMBOL(__do_once_done);