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Date: Mon, 16 Mar 2015 22:50:40 +0000
From: Al Viro <viro@ZenIV.linux.org.uk>
To: NeilBrown <neilb@suse.de>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 10/13] VFS/namei: handle LOOKUP_RCU in
 page_follow_link_light.
Message-ID: <20150316225040.GG29656@ZenIV.linux.org.uk>
References: <20150316043602.23648.52734.stgit@notabene.brown>
 <20150316044320.23648.90827.stgit@notabene.brown>
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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...