[-mm PATCH] sysdev_unregister() should call kobject_del()

[-mm PATCH] sysdev_unregister() should call kobject_del()

[Badari Pulavarty]

Hi Greg,

While playing with hotplug memory remove on 2.6.24-mm1, I 
noticed that /sysfs directory entries are not getting removed.

sysdev_unregister() used to call kobject_unregister().
But in 2.6.24-mm1, its only dropping the ref. It should
call kobject_del() to remove the object. Correct ?

With this change, the directories are getting removed
correctly. Comments ?

Thanks,
Badari

sysdev_unregister() should call kobject_del() to remove
the object.

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
---
 drivers/base/sys.c |    1 +
 1 file changed, 1 insertion(+)

Index: linux-2.6.24/drivers/base/sys.c
===================================================================
--- linux-2.6.24.orig/drivers/base/sys.c	2008-02-05 09:56:56.000000000 -0800
+++ linux-2.6.24/drivers/base/sys.c	2008-02-07 15:38:17.000000000 -0800
@@ -265,6 +265,7 @@ void sysdev_unregister(struct sys_device
 	}
 	mutex_unlock(&sysdev_drivers_lock);
 
+	kobject_del(&sysdev->kobj);
 	kobject_put(&sysdev->kobj);
 }
 

Re: [-mm PATCH] sysdev_unregister() should call kobject_del()

[Greg KH]

On Thu, Feb 07, 2008 at 03:56:58PM -0800, Badari Pulavarty wrote:
> Hi Greg,
> 
> While playing with hotplug memory remove on 2.6.24-mm1, I 
> noticed that /sysfs directory entries are not getting removed.
> 
> sysdev_unregister() used to call kobject_unregister().
> But in 2.6.24-mm1, its only dropping the ref. It should
> call kobject_del() to remove the object. Correct ?
> 
> With this change, the directories are getting removed
> correctly. Comments ?

Ick, no, this shouldn't be needed, someone else must be holding a
reference to the kobject device somewhere.  See the kobject documenation
for more info.

I'll try to see where we grab 2 references...

Have I mentioned lately that I hate the sysdev code?

ugh,

greg k-h

Re: [-mm PATCH] sysdev_unregister() should call kobject_del()

[Badari Pulavarty]

On Thu, 2008-02-07 at 16:38 -0800, Greg KH wrote:
> On Thu, Feb 07, 2008 at 03:56:58PM -0800, Badari Pulavarty wrote:
> > Hi Greg,
> > 
> > While playing with hotplug memory remove on 2.6.24-mm1, I 
> > noticed that /sysfs directory entries are not getting removed.
> > 
> > sysdev_unregister() used to call kobject_unregister().
> > But in 2.6.24-mm1, its only dropping the ref. It should
> > call kobject_del() to remove the object. Correct ?
> > 
> > With this change, the directories are getting removed
> > correctly. Comments ?
> 
> Ick, no, this shouldn't be needed, someone else must be holding a
> reference to the kobject device somewhere.  See the kobject documenation
> for more info.
> 
> I'll try to see where we grab 2 references...

I will take a closer look then. I was taking easy way out :(

Thanks,
Badari

Re: [-mm PATCH] sysdev_unregister() should call kobject_del()

[Greg KH]

On Thu, Feb 07, 2008 at 05:25:46PM -0800, Badari Pulavarty wrote:
> On Thu, 2008-02-07 at 16:38 -0800, Greg KH wrote:
> > On Thu, Feb 07, 2008 at 03:56:58PM -0800, Badari Pulavarty wrote:
> > > Hi Greg,
> > > 
> > > While playing with hotplug memory remove on 2.6.24-mm1, I 
> > > noticed that /sysfs directory entries are not getting removed.
> > > 
> > > sysdev_unregister() used to call kobject_unregister().
> > > But in 2.6.24-mm1, its only dropping the ref. It should
> > > call kobject_del() to remove the object. Correct ?
> > > 
> > > With this change, the directories are getting removed
> > > correctly. Comments ?
> > 
> > Ick, no, this shouldn't be needed, someone else must be holding a
> > reference to the kobject device somewhere.  See the kobject documenation
> > for more info.
> > 
> > I'll try to see where we grab 2 references...
> 
> I will take a closer look then. I was taking easy way out :(

Hm, I don't see anything obvious in the sys.c core.  What code is
controlling these objects that you are creating and removing from the
system?

thanks,

greg k-h

Re: [-mm PATCH] sysdev_unregister() should call kobject_del()

[Badari Pulavarty]

On Thu, 2008-02-07 at 20:55 -0800, Greg KH wrote:
> On Thu, Feb 07, 2008 at 05:25:46PM -0800, Badari Pulavarty wrote:
> > On Thu, 2008-02-07 at 16:38 -0800, Greg KH wrote:
> > > On Thu, Feb 07, 2008 at 03:56:58PM -0800, Badari Pulavarty wrote:
> > > > Hi Greg,
> > > > 
> > > > While playing with hotplug memory remove on 2.6.24-mm1, I 
> > > > noticed that /sysfs directory entries are not getting removed.
> > > > 
> > > > sysdev_unregister() used to call kobject_unregister().
> > > > But in 2.6.24-mm1, its only dropping the ref. It should
> > > > call kobject_del() to remove the object. Correct ?
> > > > 
> > > > With this change, the directories are getting removed
> > > > correctly. Comments ?
> > > 
> > > Ick, no, this shouldn't be needed, someone else must be holding a
> > > reference to the kobject device somewhere.  See the kobject documenation
> > > for more info.
> > > 
> > > I'll try to see where we grab 2 references...
> > 
> > I will take a closer look then. I was taking easy way out :(
> 
> Hm, I don't see anything obvious in the sys.c core.  What code is
> controlling these objects that you are creating and removing from the
> system?

add_memory_block()/register_memory() is creating sysfs entries
for the memory blocks.

I am trying to make use of remove_memory_block() to clean up
sysfs entries. BTW, remove_memory_block() is never tested
before, since we don't support memory remove yet.

Thanks,
Badari

Re: [-mm PATCH] sysdev_unregister() should call kobject_del()

[Greg KH]

On Thu, Feb 07, 2008 at 09:08:42PM -0800, Badari Pulavarty wrote:
> 
> On Thu, 2008-02-07 at 20:55 -0800, Greg KH wrote:
> > On Thu, Feb 07, 2008 at 05:25:46PM -0800, Badari Pulavarty wrote:
> > > On Thu, 2008-02-07 at 16:38 -0800, Greg KH wrote:
> > > > On Thu, Feb 07, 2008 at 03:56:58PM -0800, Badari Pulavarty wrote:
> > > > > Hi Greg,
> > > > > 
> > > > > While playing with hotplug memory remove on 2.6.24-mm1, I 
> > > > > noticed that /sysfs directory entries are not getting removed.
> > > > > 
> > > > > sysdev_unregister() used to call kobject_unregister().
> > > > > But in 2.6.24-mm1, its only dropping the ref. It should
> > > > > call kobject_del() to remove the object. Correct ?
> > > > > 
> > > > > With this change, the directories are getting removed
> > > > > correctly. Comments ?
> > > > 
> > > > Ick, no, this shouldn't be needed, someone else must be holding a
> > > > reference to the kobject device somewhere.  See the kobject documenation
> > > > for more info.
> > > > 
> > > > I'll try to see where we grab 2 references...
> > > 
> > > I will take a closer look then. I was taking easy way out :(
> > 
> > Hm, I don't see anything obvious in the sys.c core.  What code is
> > controlling these objects that you are creating and removing from the
> > system?
> 
> add_memory_block()/register_memory() is creating sysfs entries
> for the memory blocks.
> 
> I am trying to make use of remove_memory_block() to clean up
> sysfs entries. BTW, remove_memory_block() is never tested
> before, since we don't support memory remove yet.

So how are you testing the sysdev removal logic then if you can't remove
memory?

Oh, one thing, remove the link in unregister_memory, before you call
sysdev_unregister().  You are trying to get the name of a kobject, and
the whole object, that has just been blown away, not nice...

Which makes me believe your statement about this never being tested
before :)

thanks,

greg k-h

Re: [-mm PATCH] sysdev_unregister() should call kobject_del()

[Badari Pulavarty]

On Thu, 2008-02-07 at 21:41 -0800, Greg KH wrote:
> On Thu, Feb 07, 2008 at 09:08:42PM -0800, Badari Pulavarty wrote:
> > 
> > On Thu, 2008-02-07 at 20:55 -0800, Greg KH wrote:
> > > On Thu, Feb 07, 2008 at 05:25:46PM -0800, Badari Pulavarty wrote:
> > > > On Thu, 2008-02-07 at 16:38 -0800, Greg KH wrote:
> > > > > On Thu, Feb 07, 2008 at 03:56:58PM -0800, Badari Pulavarty wrote:
> > > > > > Hi Greg,
> > > > > > 
> > > > > > While playing with hotplug memory remove on 2.6.24-mm1, I 
> > > > > > noticed that /sysfs directory entries are not getting removed.
> > > > > > 
> > > > > > sysdev_unregister() used to call kobject_unregister().
> > > > > > But in 2.6.24-mm1, its only dropping the ref. It should
> > > > > > call kobject_del() to remove the object. Correct ?
> > > > > > 
> > > > > > With this change, the directories are getting removed
> > > > > > correctly. Comments ?
> > > > > 
> > > > > Ick, no, this shouldn't be needed, someone else must be holding a
> > > > > reference to the kobject device somewhere.  See the kobject documenation
> > > > > for more info.
> > > > > 
> > > > > I'll try to see where we grab 2 references...
> > > > 
> > > > I will take a closer look then. I was taking easy way out :(
> > > 
> > > Hm, I don't see anything obvious in the sys.c core.  What code is
> > > controlling these objects that you are creating and removing from the
> > > system?
> > 
> > add_memory_block()/register_memory() is creating sysfs entries
> > for the memory blocks.
> > 
> > I am trying to make use of remove_memory_block() to clean up
> > sysfs entries. BTW, remove_memory_block() is never tested
> > before, since we don't support memory remove yet.
> 
> So how are you testing the sysdev removal logic then if you can't remove
> memory?

I am now adding code to remove memory, I am making use of the
existing unregister_memory() code and ran into this.
> 
> Oh, one thing, remove the link in unregister_memory, before you call
> sysdev_unregister().  You are trying to get the name of a kobject, and
> the whole object, that has just been blown away, not nice...

I can add remove link before unregister() as you suggested.

Regarding accessing kobject after freeing up, no one calls with "root".
Why not clean it up first, like this ? 

Dave, are you okay with this ?

Thanks,
Badari

register_memory()/unregister_memory() never gets called with
"root". unregister_memory() is accessing kobject_name of
the object just freed up. Since no one uses the code,
lets take the code out. And also, make register_memory()
static (since unregister_memory() is already static).  

Signed-off-by: Badari Pulavarty <pbadari@us.ibm.com>
---
 drivers/base/memory.c |   20 +++++---------------
 1 file changed, 5 insertions(+), 15 deletions(-)

Index: linux-2.6.24/drivers/base/memory.c
===================================================================
--- linux-2.6.24.orig/drivers/base/memory.c	2008-02-07 16:59:52.000000000 -0800
+++ linux-2.6.24/drivers/base/memory.c	2008-02-08 08:26:33.000000000 -0800
@@ -62,8 +62,8 @@ void unregister_memory_notifier(struct n
 /*
  * register_memory - Setup a sysfs device for a memory block
  */
-int register_memory(struct memory_block *memory, struct mem_section *section,
-		struct node *root)
+static
+int register_memory(struct memory_block *memory, struct mem_section *section)
 {
 	int error;
 
@@ -71,26 +71,16 @@ int register_memory(struct memory_block 
 	memory->sysdev.id = __section_nr(section);
 
 	error = sysdev_register(&memory->sysdev);
-
-	if (root && !error)
-		error = sysfs_create_link(&root->sysdev.kobj,
-					  &memory->sysdev.kobj,
-					  kobject_name(&memory->sysdev.kobj));
-
 	return error;
 }
 
 static void
-unregister_memory(struct memory_block *memory, struct mem_section *section,
-		struct node *root)
+unregister_memory(struct memory_block *memory, struct mem_section *section)
 {
 	BUG_ON(memory->sysdev.cls != &memory_sysdev_class);
 	BUG_ON(memory->sysdev.id != __section_nr(section));
 
 	sysdev_unregister(&memory->sysdev);
-	if (root)
-		sysfs_remove_link(&root->sysdev.kobj,
-				  kobject_name(&memory->sysdev.kobj));
 }
 
 /*
@@ -361,7 +351,7 @@ static int add_memory_block(unsigned lon
 	mutex_init(&mem->state_mutex);
 	mem->phys_device = phys_device;
 
-	ret = register_memory(mem, section, NULL);
+	ret = register_memory(mem, section);
 	if (!ret)
 		ret = mem_create_simple_file(mem, phys_index);
 	if (!ret)
@@ -415,7 +405,7 @@ int remove_memory_block(unsigned long no
 	mem_remove_simple_file(mem, state);
 	mem_remove_simple_file(mem, phys_device);
 	mem_remove_simple_file(mem, removable);
-	unregister_memory(mem, section, NULL);
+	unregister_memory(mem, section);
 
 	return 0;
 }

Re: [-mm PATCH] sysdev_unregister() should call kobject_del()

[Dave Hansen]

On Fri, 2008-02-08 at 08:42 -0800, Badari Pulavarty wrote:
> 
> I can add remove link before unregister() as you suggested.
> 
> Regarding accessing kobject after freeing up, no one calls with
> "root".
> Why not clean it up first, like this ? 
> 
> Dave, are you okay with this ?

Yeah, I don't see any users of it, either.  It looks fine to me.

-- Dave

Re: [-mm PATCH] sysdev_unregister() should call kobject_del()

[Badari Pulavarty]

On Thu, 2008-02-07 at 20:55 -0800, Greg KH wrote:
> On Thu, Feb 07, 2008 at 05:25:46PM -0800, Badari Pulavarty wrote:
> > On Thu, 2008-02-07 at 16:38 -0800, Greg KH wrote:
> > > On Thu, Feb 07, 2008 at 03:56:58PM -0800, Badari Pulavarty wrote:
> > > > Hi Greg,
> > > > 
> > > > While playing with hotplug memory remove on 2.6.24-mm1, I 
> > > > noticed that /sysfs directory entries are not getting removed.
> > > > 
> > > > sysdev_unregister() used to call kobject_unregister().
> > > > But in 2.6.24-mm1, its only dropping the ref. It should
> > > > call kobject_del() to remove the object. Correct ?
> > > > 
> > > > With this change, the directories are getting removed
> > > > correctly. Comments ?
> > > 
> > > Ick, no, this shouldn't be needed, someone else must be holding a
> > > reference to the kobject device somewhere.  See the kobject documenation
> > > for more info.
> > > 
> > > I'll try to see where we grab 2 references...
> > 
> > I will take a closer look then. I was taking easy way out :(
> 
> Hm, I don't see anything obvious in the sys.c core.  What code is
> controlling these objects that you are creating and removing from the
> system?
> 

I found the culprit. Its not in sys.c core :)

remove_memory_block() takes a reference on kobject by calling
find_memory_block(). It then calls  unregister_memory() to free up sysfs
entry.
It drops only one ref (which it got at register time). So it never gets
freed up. I am going to send out a separate patch for it.

Thanks for your help.

Thanks,
Badari

Re: [-mm PATCH] sysdev_unregister() should call kobject_del()

[Greg KH]

On Fri, Feb 08, 2008 at 03:22:29PM -0800, Badari Pulavarty wrote:
> 
> On Thu, 2008-02-07 at 20:55 -0800, Greg KH wrote:
> > On Thu, Feb 07, 2008 at 05:25:46PM -0800, Badari Pulavarty wrote:
> > > On Thu, 2008-02-07 at 16:38 -0800, Greg KH wrote:
> > > > On Thu, Feb 07, 2008 at 03:56:58PM -0800, Badari Pulavarty wrote:
> > > > > Hi Greg,
> > > > > 
> > > > > While playing with hotplug memory remove on 2.6.24-mm1, I 
> > > > > noticed that /sysfs directory entries are not getting removed.
> > > > > 
> > > > > sysdev_unregister() used to call kobject_unregister().
> > > > > But in 2.6.24-mm1, its only dropping the ref. It should
> > > > > call kobject_del() to remove the object. Correct ?
> > > > > 
> > > > > With this change, the directories are getting removed
> > > > > correctly. Comments ?
> > > > 
> > > > Ick, no, this shouldn't be needed, someone else must be holding a
> > > > reference to the kobject device somewhere.  See the kobject documenation
> > > > for more info.
> > > > 
> > > > I'll try to see where we grab 2 references...
> > > 
> > > I will take a closer look then. I was taking easy way out :(
> > 
> > Hm, I don't see anything obvious in the sys.c core.  What code is
> > controlling these objects that you are creating and removing from the
> > system?
> > 
> 
> I found the culprit. Its not in sys.c core :)

Glad to hear it :)

> remove_memory_block() takes a reference on kobject by calling
> find_memory_block(). It then calls  unregister_memory() to free up sysfs
> entry.
> It drops only one ref (which it got at register time). So it never gets
> freed up. I am going to send out a separate patch for it.

Ah, nice catch.

thanks,

greg k-h