Re: [fuse-devel] [PATCH] fuse: fix occasional dentry leak when readdirplus is used

[Brian Foster <bfoster@redhat.com>]

On 07/15/2013 08:59 AM, Niels de Vos wrote:
> In case d_lookup() returns a dentry with d_inode == NULL, the dentry is
> not returned with dput(). This results in triggering a BUG() in
> shrink_dcache_for_umount_subtree():
> 
>   BUG: Dentry ...{i=0,n=...} still in use (1) [unmount of fuse fuse]
> 
> Reported-by: Justin Clift <jclift@redhat.com>
> Signed-off-by: Niels de Vos <ndevos@redhat.com>
> 
> --
> Reproducing the BUG() on kernels with fuse that support READDIRPLUS can
> be done with the GlusterFS tests:
> - http://www.gluster.org/community/documentation/index.php/Using_the_Gluster_Test_Framework
> 
> After some stressing of the VFS and fuse mountpoints, bug-860663.t will
> hit the BUG(). It does not happen on running this test stand-alone.

Hi Neils,

FYI, this is fairly easy to reproduce on-demand with gluster:

- mount a volume to two local mountpoints (i.e., I used a single
storage/posix translator volume):
	glusterfs --volfile=./test.vol /mnt/{1,2} --use-readdirp=1
- create a negative dentry in one mountpoint:
	ls /mnt/1/file (results in ENOENT)
- create the file via the second mountpoint:
	touch /mnt/2/file
- run a readdirp on the first mountpoint:
	ls /mnt/1/
- umount /mnt/2 /mnt/1

> ---
>  fs/fuse/dir.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
> index 0eda527..da67a15 100644
> --- a/fs/fuse/dir.c
> +++ b/fs/fuse/dir.c
> @@ -1246,7 +1246,9 @@ static int fuse_direntplus_link(struct file *file,
>  		if (err)
>  			goto out;
>  		dput(dentry);
> -		dentry = NULL;
> +	} else if (dentry) {
> +		/* this dentry does not have a d_inode, just drop it */
> +		dput(dentry);
>  	}

I'm not really familiar with the dcache code, but is it appropriate to
also d_invalidate() the dentry in this case (as the previous code block
does)? Perhaps Miklos or somebody more familiar with dcache can confirm...

Brian

>  
>  	dentry = d_alloc(parent, &name);
>