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Date: Wed, 2 Aug 2006 21:54:51 +0200
From: Willy Tarreau <w@1wt.eu>
To: Jeff Layton <jlayton@poochiereds.net>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] 2.4 client - update d_cache when server reports ENOENT on an NFS remove
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On Mon, Jul 31, 2006 at 07:39:25AM -0400, Jeff Layton wrote:
> Anuwat Phrukphicharn of HP discovered and patched this problem in
> RHEL-3, and asked that I push it upstream.
> 
> When the 2.4 NFS client does a REMOVE and gets an ENOENT back from the
> server it does not remove the dentry from the d_cache. This can make it
> inappropriately keep writing to an inode that has been renamed.
> 
> To reproduce, run this on an NFS server with /scratch exported:
> 
> #!/bin/sh
> dir=/scratch/98201
> mkdir -p $dir/recv
> cat /dev/null > $dir/recv/x
> while true; do
>         length=`wc -l $dir/recv/x | cut -d' ' -f1`
>         if [ ${length} -gt 1 ]; then
>                 echo "problem occured!"
>                 date
>                 exit 1
>         fi
>         mv $dir/x $dir/recv/x
>         sleep 1
> done
> 
> 
> ...and then do this on the client:
> 
> mount server:/scratch /mnt/server
> while true; do
>         rm -f /mnt/server/98201/x
>         date >> /mnt/server/98201/x
>         usleep 100
> done
> 
> The file "x" should never contain more than 1 line, but occasionally,
> the server will report an ENOENT back to the client (indicating that the
> server script has renamed the file before the rm could occur). After
> this, the client will keep appending to the same inode, even though the
> file has been renamed.
> 
> I've not seen this problem in 2.6 kernels, but I've not done any
> extensive testing there as of yet so I can't confirm whether it's still
> a problem there or not.
> 
> A patch to fix this follows. It just makes ENOENT a special case when
> handling errors in the nfs_safe_remove function, and lets the client
> update the dcache as if the remove had succeeded. The ENOENT is still
> reported back to userspace. This corrected the problem on my test rig
> and for the reporter as well:
> 
> Signed-off-by: Jeff Layton <jlayton@poochiereds.net>
> 
> --- linux-2.4.21/fs/nfs/dir.c.unlink-enoent
> +++ linux-2.4.21/fs/nfs/dir.c
> @@ -1023,7 +1023,10 @@ static int nfs_safe_remove(struct dentry
>  	if (inode)
>  		NFS_CACHEINV(inode);
>  	error = NFS_PROTO(dir)->remove(dir, &dentry->d_name);
> -	if (error < 0)
> +
> +	/* if server returned ENOENT, assume that the dentry is already gone
> +	 * and update the cache accordingly */
> +	if (error < 0 && (error != -ENOENT))
>  		goto out;
>  	if (inode)
>  		inode->i_nlink--;
> 
> 

Thanks very much for your patch Jeff, I'm queueing it for 2.4.34.

Cheers,
Willy