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Message-ID: <20070420063714.GA5205@infradead.org>
Date: Fri, 20 Apr 2007 07:37:14 +0100
From: Christoph Hellwig <hch@...radead.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: "Eric W. Biederman" <ebiederm@...ssion.com>,
containers@...ts.osdl.org, Oleg Nesterov <oleg@...sign.ru>,
Christoph Hellwig <hch@...radead.org>,
linux-kernel@...r.kernel.org,
Andrew de Quincey <adq_dvb@...skialf.net>,
Mauro Carvalho Chehab <mchehab@...radead.org>
Subject: Re: [PATCH] dvb_en_50221: Convert to kthread API
On Thu, Apr 19, 2007 at 03:34:13PM -0700, Andrew Morton wrote:
> On Thu, 19 Apr 2007 01:59:04 -0600
> "Eric W. Biederman" <ebiederm@...ssion.com> wrote:
>
> > This patch is a minimal transformation to use the kthread API
> > doing it's best to preserve the existing logic.
> >
> > Instead of starting kdvb-ca by calling kernel_thread,
> > daemonize and sigfillset we kthread_run is used.
> >
> > Instead of tracking the pid of the running thread we instead
> > simply keep a flag to indicate that the current thread is
> > running, as that is all the pid is really used for.
> >
> > And finally the kill_proc sending signal 0 to the kernel thread to
> > ensure it is alive before we wait for it to shutdown is removed.
> > The kthread API does not provide the pid so we don't have that
> > information readily available and the test is just silly. If there
> > is no shutdown race the test is a useless confirmation of that the
> > thread is running. If there is a race the test doesn't fix it and
> > we should fix the race properly.
>
> urgh, yes, this is just sad. We should convert this driver fully to
> the kthread API - it will end up much better.
>
> I'll queue this up as a -mm-only thing as a gentle reminder that
> we should do it properly.
Here's an attempted update to the full kthread API + wake_up_process:
Index: linux-2.6/drivers/media/dvb/dvb-core/dvb_ca_en50221.c
===================================================================
--- linux-2.6.orig/drivers/media/dvb/dvb-core/dvb_ca_en50221.c 2007-04-20 07:25:07.000000000 +0200
+++ linux-2.6/drivers/media/dvb/dvb-core/dvb_ca_en50221.c 2007-04-20 07:35:54.000000000 +0200
@@ -37,6 +37,7 @@
#include <linux/delay.h>
#include <linux/spinlock.h>
#include <linux/sched.h>
+#include <linux/kthread.h>
#include "dvb_ca_en50221.h"
#include "dvb_ringbuffer.h"
@@ -140,13 +141,7 @@ struct dvb_ca_private {
wait_queue_head_t wait_queue;
/* PID of the monitoring thread */
- pid_t thread_pid;
-
- /* Wait queue used when shutting thread down */
- wait_queue_head_t thread_queue;
-
- /* Flag indicating when thread should exit */
- unsigned int exit:1;
+ struct task_struct *thread;
/* Flag indicating if the CA device is open */
unsigned int open:1;
@@ -902,28 +897,10 @@ static void dvb_ca_en50221_thread_wakeup
ca->wakeup = 1;
mb();
- wake_up_interruptible(&ca->thread_queue);
+ wake_up_process(ca->thread);
}
/**
- * Used by the CA thread to determine if an early wakeup is necessary
- *
- * @param ca CA instance.
- */
-static int dvb_ca_en50221_thread_should_wakeup(struct dvb_ca_private *ca)
-{
- if (ca->wakeup) {
- ca->wakeup = 0;
- return 1;
- }
- if (ca->exit)
- return 1;
-
- return 0;
-}
-
-
-/**
* Update the delay used by the thread.
*
* @param ca CA instance.
@@ -982,7 +959,6 @@ static void dvb_ca_en50221_thread_update
static int dvb_ca_en50221_thread(void *data)
{
struct dvb_ca_private *ca = data;
- char name[15];
int slot;
int flags;
int status;
@@ -991,28 +967,17 @@ static int dvb_ca_en50221_thread(void *d
dprintk("%s\n", __FUNCTION__);
- /* setup kernel thread */
- snprintf(name, sizeof(name), "kdvb-ca-%i:%i", ca->dvbdev->adapter->num, ca->dvbdev->id);
-
- lock_kernel();
- daemonize(name);
- sigfillset(¤t->blocked);
- unlock_kernel();
-
/* choose the correct initial delay */
dvb_ca_en50221_thread_update_delay(ca);
/* main loop */
- while (!ca->exit) {
+ while (!kthread_should_stop()) {
/* sleep for a bit */
- if (!ca->wakeup) {
- flags = wait_event_interruptible_timeout(ca->thread_queue,
- dvb_ca_en50221_thread_should_wakeup(ca),
- ca->delay);
- if ((flags == -ERESTARTSYS) || ca->exit) {
- /* got signal or quitting */
- break;
- }
+ while (!ca->wakeup) {
+ set_current_state(TASK_INTERRUPTIBLE);
+ schedule_timeout(ca->delay);
+ if (kthread_should_stop())
+ return 0;
}
ca->wakeup = 0;
@@ -1181,10 +1146,6 @@ static int dvb_ca_en50221_thread(void *d
}
}
- /* completed */
- ca->thread_pid = 0;
- mb();
- wake_up_interruptible(&ca->thread_queue);
return 0;
}
@@ -1682,9 +1643,6 @@ int dvb_ca_en50221_init(struct dvb_adapt
goto error;
}
init_waitqueue_head(&ca->wait_queue);
- ca->thread_pid = 0;
- init_waitqueue_head(&ca->thread_queue);
- ca->exit = 0;
ca->open = 0;
ca->wakeup = 0;
ca->next_read_slot = 0;
@@ -1710,14 +1668,14 @@ int dvb_ca_en50221_init(struct dvb_adapt
mb();
/* create a kthread for monitoring this CA device */
-
- ret = kernel_thread(dvb_ca_en50221_thread, ca, 0);
-
- if (ret < 0) {
- printk("dvb_ca_init: failed to start kernel_thread (%d)\n", ret);
+ ca->thread = kthread_run(dvb_ca_en50221_thread, ca, "kdvb-ca-%i:%i",
+ ca->dvbdev->adapter->num, ca->dvbdev->id);
+ if (IS_ERR(ca->thread)) {
+ ret = PTR_ERR(ca->thread);
+ printk("dvb_ca_init: failed to start kernel_thread (%d)\n",
+ ret);
goto error;
}
- ca->thread_pid = ret;
return 0;
error:
@@ -1748,17 +1706,7 @@ void dvb_ca_en50221_release(struct dvb_c
dprintk("%s\n", __FUNCTION__);
/* shutdown the thread if there was one */
- if (ca->thread_pid) {
- if (kill_proc(ca->thread_pid, 0, 1) == -ESRCH) {
- printk("dvb_ca_release adapter %d: thread PID %d already died\n",
- ca->dvbdev->adapter->num, ca->thread_pid);
- } else {
- ca->exit = 1;
- mb();
- dvb_ca_en50221_thread_wakeup(ca);
- wait_event_interruptible(ca->thread_queue, ca->thread_pid == 0);
- }
- }
+ kthread_stop(ca->thread);
for (i = 0; i < ca->slot_count; i++) {
dvb_ca_en50221_slot_shutdown(ca, i);
-
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