How to safely access inode/dentry obtained from struct page *?

[Joshi]

I am trying to obtain file name at block layer level (above IO scheduler).
At this level I receive bio structure, within which page pointers are kept.

Thereby I do following to obtain the inode and dentry -

struct inode *inode_ptr = page->mapping->host;
if (inode_ptr != NULL)
/* Access dentry i.e. i_dentry in the inode */


This works usually. But problem is, inode and dentry may get released
from inode and dentry cache at any time.
While accessing inode/dentry I need to ensure that till the time I am
accessing'em these structure remain valid in memory.
Is it possible to ensure that? Which structures/locks I need to check
for the purpose.

Appreciate any help.

Thanks!

-- 
Joshi