linux-kernel - Re: [PATCH 10/13] VFS/namei: handle LOOKUP_RCU in page_follow_link

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Message-ID: <20150316225040.GG29656@ZenIV.linux.org.uk>
Date:	Mon, 16 Mar 2015 22:50:40 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	NeilBrown <neilb@...e.de>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/13] VFS/namei: handle LOOKUP_RCU in
 page_follow_link_light.

On Mon, Mar 16, 2015 at 03:43:20PM +1100, NeilBrown wrote:
> +	char *kaddr;
> +	struct page *page;
> +	struct address_space *mapping = dentry->d_inode->i_mapping;

Who said that dentry->d_inode hasn't gone NULL by that point?

> +	nd_terminate_link(kaddr, dentry->d_inode->i_size, PAGE_SIZE - 1);

... or changed here.  Again, dentry->d_inode is stable only if you are
holding a reference to dentry.  That's why we have those dances around
nd->inode, for example.  Doing unlazy_walk() is enough to stabilize the
damn thing, so currently ->follow_link() doesn't have to worry about it.
With your changes, though...
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