Re: kernel BUG at include/linux/dcache.h:271!

[Andrew Morton <akpm@digeo.com>]

Maneesh Soni <maneesh@in.ibm.com> wrote:
>
> The problem is that we have multiple ramdisks but all have
> common request queue and common elevator. In terms of sysfs we 
> have multiple kobjects for multiple ramdisks, but one single kobject for the 
> ramdisks' common elevator. 
> 
> While initializing, different kobjects are allocated for the ramdisks but,
> the common elevator uses the same kobject. In other words, every init
> of a ramdisk, the common elevator.kobj->parent will be different and it will
> allocate a new dentry, overwrite the elevator.kobj->dentry
> and loose the earlier allocated dentries. (see: elv_register_queue())
> 
> While exiting, it ends up in removing the same dentry (allocated at the last)
> again and BUGs in dget on dentry with zero ref count.
> 
> Not sure where it should be fixed 
> ramdisk 
>  - should have separate queues on for each ramdisk
> 
> elevator 
>  - should not re-register already registered queue in elv_register_queue
> 
> sysfs 
>  - should handle kobject with multiple parent kobjects 

I can't think of anywhere else where we are likely to want to support
multiple devices from a single queue in this manner, so perhaps the best
solution is to remove the exceptional case: allocate a separate queue for
each ramdisk instance.

Jens, do you agree?