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Date: Wed, 10 Apr 2002 16:53:19 -0400 (EDT)
From: Alexander Viro <viro@math.psu.edu>
To: Andrew Morton <akpm@zip.com.au>
cc: lkml <linux-kernel@vger.kernel.org>
Subject: Re: [prepatch] address_space-based writeback
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On Wed, 10 Apr 2002, Andrew Morton wrote:

[I'll answer to the rest when I get some sleep]

> The one thing which does worry me a bit is why __mark_inode_dirty
> tests for a null ->i_sb.  If the inode doesn't have a superblock
> then its pages are hidden from the writeback functions.
> 
> This is not fatal per-se.  The pages are still visible to the VM
> via the LRU, and presumably the filesystem knows how to sync
> its own stuff.  But for memory-balancing and throttling purposes,
> I'd prefer that the null ->i_sb not be allowed.  Where can this
> occur?

In rather old kernels.  IOW, these checks are atavisms - these days
_all_ inodes have (constant) ->i_sb.  The only way to create an
in-core inode is alloc_inode(superblock) and requires superblock
to be non-NULL.  After that ->i_sb stays unchanged (and non-NULL)
until struct inode is freed.

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