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

Alex Chiang
2009-03-11T18:42:40Z

* Greg KH <gregkh@suse.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@suse.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;
}