On Sat, 17 Sep 2005, Andrew Morton wrote:
> > > That code could be converted to the kthread API btw.
> >
> > Hmph. Near as I can tell, the only changes that would involve are:
> >
> > Converting the thread creation call from kernel_thread to
> > kthread_run.
> >
> > Adding another call to wake the thread up once it has been
> > created.
> >
> > Removing the call to daemonize.
> >
> > There wouldn't be any need to call kthread_stop -- and in fact it wouldn't
> > work, as the thread waits on a semaphore while it is idle (kthread_stop
> > can't cope with things like that).
>
> Well I was assuming that the semaphore would go away as well. Kernel
> threads normally use waitqueues to await more work.
Some kernel threads have a producer-consumer relationship with their
clients, and it's important that they wake exactly once each time they are
invoked. A semaphore is the natural way to manage such a thread, but the
kthread API isn't set up to handle such things. It's possible to make
this work, by using a manual poor-man's semaphore implementation, but that
seems ridiculous.
Would this patch be acceptable?
Alan Stern
Enhance the kthread API so that it can be used with threads that wait on a
semaphore when they are idle.
Signed-off-by: Alan Stern <[email protected]>
--- a/include/linux/kthread.h Mon Sep 12 23:12:09 2005
+++ b/include/linux/kthread.h Sat Sep 17 23:24:59 2005
@@ -67,7 +67,19 @@
*
* Returns the result of threadfn(), or -EINTR if wake_up_process()
* was never called. */
-int kthread_stop(struct task_struct *k);
+#define kthread_stop(k) kthread_stop_sem(k, NULL)
+
+/**
+ * kthread_stop_sem: stop a thread created by kthread_create().
+ * @k: thread created by kthread_create().
+ * @s: semaphore that @k waits on while idle.
+ *
+ * Does essentially the same thing as kthread_stop() above, but wakes
+ * @k by calling up(@s).
+ *
+ * Returns the result of threadfn(), or -EINTR if wake_up_process()
+ * was never called. */
+int kthread_stop_sem(struct task_struct *k, struct semaphore *s);
/**
* kthread_should_stop: should this kthread return now?
--- a/kernel/kthread.c Mon Sep 12 23:12:09 2005
+++ b/kernel/kthread.c Sat Sep 17 23:19:08 2005
@@ -163,7 +163,7 @@
}
EXPORT_SYMBOL(kthread_bind);
-int kthread_stop(struct task_struct *k)
+int kthread_stop_sem(struct task_struct *k, struct semaphore *s)
{
int ret;
@@ -178,7 +178,10 @@
/* Now set kthread_should_stop() to true, and wake it up. */
kthread_stop_info.k = k;
- wake_up_process(k);
+ if (s)
+ up(s);
+ else
+ wake_up_process(k);
put_task_struct(k);
/* Once it dies, reset stop ptr, gather result and we're done. */
@@ -189,7 +192,7 @@
return ret;
}
-EXPORT_SYMBOL(kthread_stop);
+EXPORT_SYMBOL(kthread_stop_sem);
static __init int helper_init(void)
{
-
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