UBI memory leak after creating and removing volumes

[John.Smith at pace.com]

Artem Bityutskiy wrote:
>
> On Tue, 2009-02-17 at 12:01 +0000, John.Smith at pace.com wrote:
> 
> > Hello, 
> 
> > I am using a 2.6.18 Kernel, patched with MTD from Kernel 2.6.21, and
> > UBI from the mainline kernel a few days later on 1 May 2007.  The
> > whole is running on an embedded MIPS device.
> >
> > I have NAND, and UBI, and gluebi, and jffs2.  I use jffs2, mounted
> > on an mtdblock device. Broadly, it all works.
> > 
> > I am experiencing a memory leak revealed in recent stress tests.
The
> > stress tests create and delete many UBI volumes, and are are broadly
> > equivelent to the following:
> 
> Can you please enable /proc/slab_allocators - it tracks all allocators
> and if we have a leak - it may point to the function which is guilty.
> 
> Recompile the kernel, and you will have a nice instrumentation to find
> memory leak - the /proc/slab_allocators file. Please, play with this.

After 0, 1000 and 2000 iterations of a test of creating 2 UBI volumes,
then removing them, /proc/slab_allocators shows these three items
obviously increasing:

inode_cache: 327 alloc_inode+0x140/0x148         
inode_cache: 3329 alloc_inode+0x140/0x148        
inode_cache: 6329 alloc_inode+0x140/0x148        
(3 objects per iteration)

sysfs_dir_cache: 1402 sysfs_new_dirent+0x2c/0xa0 
sysfs_dir_cache: 15402 sysfs_new_dirent+0x2c/0xa0
sysfs_dir_cache: 29402 sysfs_new_dirent+0x2c/0xa0
(14 objects per iteration)

dentry_cache: 669 d_alloc+0x30/0x214             
dentry_cache: 3823 d_alloc+0x30/0x214            
dentry_cache: 6823 d_alloc+0x30/0x214            
(3 objects per iteration)

I don't know how to track these things down fully. But I 
believe they relate to the elevator queue.

I added some printks to elv_register_queue and __elv_unregister_queue
so the functions are like:

int elv_register_queue(struct request_queue *q)
{
   elevator_t *e = q->elevator;

   printk("elv_register_queue: e->kobj.dentry at %p val %p\n", 
          &e->kobj.dentry, e->kobj.dentry );
 
   kobject_add(&e->kobj);
   /* Do more stuff */  

   printk("elv_register_queue: e->kobj.dentry at %p val %p AFTER\n", 
          &e->kobj.dentry, e->kobj.dentry );
}

static void __elv_unregister_queue(elevator_t *e)
{
   printk("__elv_unregister_queue: e->kobj.dentry at %p val %p\n", 
          &e->kobj.dentry, e->kobj.dentry );

   kobject_uevent(&e->kobj, KOBJ_REMOVE);
   kobject_del(&e->kobj);

   printk("__elv_unregister_queue: e->kobj.dentry at %p val %p AFTER\n",

          &e->kobj.dentry, e->kobj.dentry );
}

When creating and deleting volumes, e->kobj.dentry is always at the
same address. 

After the register_queue operation, e->kobj.dentry points to a new
dentry. So e->kobj.dentry is getting over-written.

After the unregister_queue operation, e->kobj.dentry is NULL.  The
kobject_del calls sysfs_remove_dir which either does or does not
delete memory according to whether e->kobj.dentry is NULL. So
the second ubi fails.

But I don't know what to do plug the leak.

Regards,
John

John Smith
 
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