linux-kernel - Re: [PATCH] mtd_blkdevs: Convert to use the kthread API

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Message-Id: <1177248180.2755.12.camel@pmac.infradead.org>
Date:	Sun, 22 Apr 2007 14:23:00 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"<Andrew Morton" <akpm@...l.org>, containers@...ts.osdl.org,
	Oleg Nesterov <oleg@...sign.ru>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd_blkdevs: Convert to use the kthread API

On Sun, 2007-04-22 at 13:24 +0100, Christoph Hellwig wrote:
> This is the full conversion I sent to Dave in April 2006, but never
> got any feedback to:

Sorry about that; I need prodding sometimes. I'll provide some now... 

Can you show me why the thread won't now miss a wakeup if it goes to
sleep just as a new request is added to its queue?

Having already applied Eric's patch, this is the delta to yours...

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
index 1aa018a..d065dba 100644
--- a/drivers/mtd/mtd_blkdevs.c
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -29,9 +29,7 @@ extern struct mutex mtd_table_mutex;
 extern struct mtd_info *mtd_table[];
 
 struct mtd_blkcore_priv {
-	struct completion thread_dead;
-	int exiting;
-	wait_queue_head_t thread_wq;
+	struct task_struct *thread;
 	struct request_queue *rq;
 	spinlock_t queue_lock;
 };
@@ -85,26 +83,18 @@ static int mtd_blktrans_thread(void *arg)
 	current->flags |= PF_MEMALLOC | PF_NOFREEZE;
 
 	spin_lock_irq(rq->queue_lock);
-
-	while (!tr->blkcore_priv->exiting) {
+	while (!kthread_should_stop()) {
 		struct request *req;
 		struct mtd_blktrans_dev *dev;
 		int res = 0;
-		DECLARE_WAITQUEUE(wait, current);
 
 		req = elv_next_request(rq);
 
 		if (!req) {
-			add_wait_queue(&tr->blkcore_priv->thread_wq, &wait);
-			set_current_state(TASK_INTERRUPTIBLE);
-
 			spin_unlock_irq(rq->queue_lock);
-
+			set_current_state(TASK_INTERRUPTIBLE);
 			schedule();
-			remove_wait_queue(&tr->blkcore_priv->thread_wq, &wait);
-
 			spin_lock_irq(rq->queue_lock);
-
 			continue;
 		}
 
@@ -123,13 +113,13 @@ static int mtd_blktrans_thread(void *arg)
 	}
 	spin_unlock_irq(rq->queue_lock);
 
-	complete_and_exit(&tr->blkcore_priv->thread_dead, 0);
+	return 0;
 }
 
 static void mtd_blktrans_request(struct request_queue *rq)
 {
 	struct mtd_blktrans_ops *tr = rq->queuedata;
-	wake_up(&tr->blkcore_priv->thread_wq);
+	wake_up_process(tr->blkcore_priv->thread);
 }
 
 
@@ -355,7 +345,6 @@ static struct mtd_notifier blktrans_notifier = {
 
 int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 {
-	struct task_struct *task;
 	int ret, i;
 
 	/* Register the notifier if/when the first device type is
@@ -379,8 +368,6 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 		return ret;
 	}
 	spin_lock_init(&tr->blkcore_priv->queue_lock);
-	init_completion(&tr->blkcore_priv->thread_dead);
-	init_waitqueue_head(&tr->blkcore_priv->thread_wq);
 
 	tr->blkcore_priv->rq = blk_init_queue(mtd_blktrans_request, &tr->blkcore_priv->queue_lock);
 	if (!tr->blkcore_priv->rq) {
@@ -394,13 +381,14 @@ int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	blk_queue_hardsect_size(tr->blkcore_priv->rq, tr->blksize);
 	tr->blkshift = ffs(tr->blksize) - 1;
 
-	task = kthread_run(mtd_blktrans_thread, tr, "%sd", tr->name);
-	if (IS_ERR(task)) {
+	tr->blkcore_priv->thread = kthread_run(mtd_blktrans_thread, tr,
+			"%sd", tr->name);
+	if (IS_ERR(tr->blkcore_priv->thread)) {
 		blk_cleanup_queue(tr->blkcore_priv->rq);
 		unregister_blkdev(tr->major, tr->name);
 		kfree(tr->blkcore_priv);
 		mutex_unlock(&mtd_table_mutex);
-		return PTR_ERR(task);
+		return PTR_ERR(tr->blkcore_priv->thread);
 	}
 
 	INIT_LIST_HEAD(&tr->devs);
@@ -423,9 +411,7 @@ int deregister_mtd_blktrans(struct mtd_blktrans_ops *tr)
 	mutex_lock(&mtd_table_mutex);
 
 	/* Clean up the kernel thread */
-	tr->blkcore_priv->exiting = 1;
-	wake_up(&tr->blkcore_priv->thread_wq);
-	wait_for_completion(&tr->blkcore_priv->thread_dead);
+	kthread_stop(tr->blkcore_priv->thread);
 
 	/* Remove it from the list of active majors */
 	list_del(&tr->list);


-- 
dwmw2

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