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

[Pranay Srivastava]

On 30-Aug-2014 10:49 AM, "Joshi" <joshiiitr at gmail.com> wrote:
>
> 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 */
>

Are you doing this in readpage(s) or writepage(s) callback? If that's the
case your page would be locked and dentry/inode wouldn't go away.

If you are doing something else then first make sure you do lock_page and
proceed only if you get that page lock.

Second you can try dget and dput before you start working with dentry.

>
> 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.

is this your observation from your test case? Can you explain your test
case a bit.
>
> Appreciate any help.
>
> Thanks!
>
> --
> Joshi
>
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