Re: jbd2_handle and i_data_sem circular locking dependency detected

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

On Mon, Mar 10, 2008 at 03:24:26PM +0100, Jan Kara wrote:
> > This one came up again when i was doing the mmap ENOSPC patch. Now the
> > current code with migrate is taking i_mutex to protech against all
> > writes. But it seems a write to a mmap area mapping a hole can still go
> > through fine. And that path cannot take i_mutex.
> > 
> > So i guess the migrate locking need to be fixed. Any suggestion ?
>   Hmm, thinking about it a bit more.  One possibility is that we could just
> use i_mutex to protect against ordinary writes, and before swapping blocks
> for extents we'd check whether some holes were not filled in the mean time.
> If yes, we can retry the migrate, or fail it and retry later.
>   Another possibility would be to make ext4 use page_mkwrite to fill in
> holes. There we could safely acquire i_mutex and be done.
> 

page_mkwrite is called with mmap_sem help and we can't take inode->i_mutex
in page_mkwrite. The DIO write have inode->i_mutex ->  mmap_sem 
locking order.

I "fixed" it by introducing i_migrate_sem

http://article.gmane.org/gmane.comp.file-systems.ext4/5402

-aneesh