linux-kernel - Re: Regression with initramfs and nfsroot (appears to be in the dcache)

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Date:	Fri, 30 Nov 2012 18:18:17 -0800
From:	Simon Kirby <sim@...tway.ca>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Patrick McLean <patrick@....mcgill.ca>,
	Patrick McLean <patrickm@...kai.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	linux-nfs@...r.kernel.org
Subject: Re: Regression with initramfs and nfsroot (appears to be in the
 dcache)

On Fri, Nov 30, 2012 at 02:00:48AM +0000, Al Viro wrote:

> OK, that settles it.  WARN_ON() and printks in the area can be dropped;
> the right fix is below.  However, there's a similar place in cifs that
> also needs to be dealt with and I really, really wonder why the hell do
> we do d_drop() in nfs_revalidate_lookup().  It's not relevant in this
> bug, but I would like to understand what's wrong with simply returning
> 0 from ->d_revalidate() and letting the caller (in fs/namei.c) take care
> of unhashing, etc. itself.  Would make have_submounts() in there pointless
> as well - we could just return 0 and let d_invalidate() take care of the
> checks...  Trond?
> 
> diff --git a/fs/nfs/dir.c b/fs/nfs/dir.c
> --- a/fs/nfs/dir.c
> +++ b/fs/nfs/dir.c
> @@ -450,7 +450,8 @@ void nfs_prime_dcache(struct dentry *parent, struct nfs_entry *entry)
>  			nfs_refresh_inode(dentry->d_inode, entry->fattr);
>  			goto out;
>  		} else {
> -			d_drop(dentry);
> +			if (d_invalidate(dentry) != 0)
> +				goto out;
>  			dput(dentry);
>  		}
>  	}

Hello,

With your previous patch (with the WARN_ON), I hit the WARN_ON() in the
test case described here: https://patchwork.kernel.org/patch/1446851/ .
The __d_move()ing mountpoint case no longer hits, and there is no longer
an EBUSY, so this seems to work for me (in 3.6, where it broke).

Simon-
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