linux-kernel - Re: [PATCH, RFC] sysfs: only allow one scheduled removal callback per kobj

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Date:	Wed, 11 Mar 2009 12:42:25 -0600
From:	Alex Chiang <achiang@...com>
To:	Greg KH <gregkh@...e.de>
Cc:	Cornelia Huck <cornelia.huck@...ibm.com>,
	Vegard Nossum <vegard.nossum@...il.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Ingo Molnar <mingo@...e.hu>, jbarnes@...tuousgeek.org,
	tj@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH, RFC] sysfs: only allow one scheduled removal callback
	per kobj

* Greg KH <gregkh@...e.de>:
> On Wed, Mar 11, 2009 at 06:47:29PM +0100, Cornelia Huck wrote:
> > On Wed, 11 Mar 2009 08:32:28 -0700,
> > Greg KH <gregkh@...e.de> wrote:
> > 
> > > Why can't you use device_unregister()?  Or, you could use device_del(),
> > > which lets you rely on the fact that the device structure is still
> > > around for a bit, but it will disappear from sysfs.  Just don't forget
> > > to do the final put_device() on it to free the memory and "really"
> > > release it.
> > > 
> > > Or am I missing something else here?
> > 
> > You can't unregister a device from one of its attribute callbacks,
> 
> Doh!  You're right, very sorry Alex for missing this.

That's ok.

> > (For the original oops, I'd rather solve the problem by making sure the
> > caller doesn't trigger removal several times - should probably be less
> > code than the proposed patch?)
> 
> Any ideas on how to do this?

I still think the original patch I proposed is the right answer.

/ac
---
 file.c |   23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)
---
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index 1f4a3f8..e05a172 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -659,13 +659,16 @@ void sysfs_remove_file_from_group(struct kobject *kobj,
 EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);
 
 struct sysfs_schedule_callback_struct {
-	struct kobject 		*kobj;
+	struct list_head	workq_list;
+	struct kobject		*kobj;
 	void			(*func)(void *);
 	void			*data;
 	struct module		*owner;
 	struct work_struct	work;
 };
 
+static DEFINE_MUTEX(sysfs_workq_mutex);
+static LIST_HEAD(sysfs_workq);
 static void sysfs_schedule_callback_work(struct work_struct *work)
 {
 	struct sysfs_schedule_callback_struct *ss = container_of(work,
@@ -674,6 +677,9 @@ static void sysfs_schedule_callback_work(struct work_struct *work)
 	(ss->func)(ss->data);
 	kobject_put(ss->kobj);
 	module_put(ss->owner);
+	mutex_lock(&sysfs_workq_mutex);
+	list_del(&ss->workq_list);
+	mutex_unlock(&sysfs_workq_mutex);
 	kfree(ss);
 }
 
@@ -700,10 +706,19 @@ static void sysfs_schedule_callback_work(struct work_struct *work)
 int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
 		void *data, struct module *owner)
 {
-	struct sysfs_schedule_callback_struct *ss;
+	struct sysfs_schedule_callback_struct *ss, *tmp;
 
 	if (!try_module_get(owner))
 		return -ENODEV;
+
+	mutex_lock(&sysfs_workq_mutex);
+	list_for_each_entry_safe(ss, tmp, &sysfs_workq, workq_list)
+		if (ss->kobj == kobj) {
+			mutex_unlock(&sysfs_workq_mutex);
+			return -EBUSY;
+		}
+	mutex_unlock(&sysfs_workq_mutex);
+
 	ss = kmalloc(sizeof(*ss), GFP_KERNEL);
 	if (!ss) {
 		module_put(owner);
@@ -715,6 +730,10 @@ int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
 	ss->data = data;
 	ss->owner = owner;
 	INIT_WORK(&ss->work, sysfs_schedule_callback_work);
+	INIT_LIST_HEAD(&ss->workq_list);
+	mutex_lock(&sysfs_workq_mutex);
+	list_add_tail(&ss->workq_list, &sysfs_workq);
+	mutex_unlock(&sysfs_workq_mutex);
 	schedule_work(&ss->work);
 	return 0;
 }
--
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