Re: nullfs: panic: vrele: negative ref cnt

On Mon, Mar 09, 2009 at 04:42:25PM -0400, John Baldwin wrote:
> On Monday 09 March 2009 9:15:22 am Paul B. Mahol wrote:
> > Hi,
> > here is part of textdump:
> > 
> > panic(c061db9e,0,c061cee6,88e,4,...) at panic+0x136
> > vrele(c4326d9c,0,c433fb5f,82,c060f3c7,...) at vrele+0x111
> > null_nodeget(c3fd4780,c4326d9c,c3ba8bf4,0,c3ba8be4,...) at null_nodeget+0xa0
> > null_bypass(c3ba8be0,c3f35a78,c3ba8c28) at null_bypass+0x141
> > VOP_VPTOCNP_APV(c4340240,c3ba8be0,c061bf01,387,c3cecc00,...) at
> > VOP_VPTOCNP_APV+0xb3
> 
> Try this.  null_bypass() can't handle VOP_VPTOCNP because VPTOCNP doesn't 
> return a vnode that is locked and VREF'd, but just a vnode that is vhold()'d.  
> This patch attempts to give nullfs a VOP_VPTONCP() method which remaps the 
> directory vnode properly on return by locking the directory vnode while 
> invoking null_nodeget().
> 
> --- //depot/user/jhb/lock/fs/nullfs/null_vnops.c
> +++ /home/jhb/work/p4/lock/fs/nullfs/null_vnops.c
> _at__at_ -722,6 +722,34 _at__at_
>  	return VOP_VPTOFH(lvp, ap->a_fhp);
>  }
>  
> +static int
> +null_vptocnp(struct vop_vptocnp_args *ap)
> +{
> +	struct vnode *lvp, *dvp;
> +	int error;
> +
> +	/*
> +	 * We can't use null_bypass() because 'dvp' is not returned
> +	 * locked.  It is merely 'vhold()'ed.
> +	 */
> +	lvp = NULLVPTOLOWERVP(ap->a_vp);
> +	error = VOP_VPTOCNP(lvp, &dvp, ap->a_buf, ap->a_buflen);
> +	if (error)
> +		return (error);
> +
> +	/*
> +	 * Map 'dvp' to the corresponding null node.  We have to lock
> +	 * it before calling null_nodeget().
> +	 */
> +	vn_lock(dvp, LK_SHARED | LK_RETRY);
> +	error = null_nodeget(ap->a_vp->v_mount, dvp, ap->a_vpp);
> +	if (error) {
> +		vrele(dvp);
> +		vdrop(dvp);
> +	}
> +	return (error);
> +}
> +
>  /*
>   * Global vfs data structures
>   */
> _at__at_ -743,4 +771,5 _at__at_
>  	.vop_strategy =		VOP_EOPNOTSUPP,
>  	.vop_unlock =		null_unlock,
>  	.vop_vptofh =		null_vptofh,
> +	.vop_vptocnp =		null_vptocnp,
>  };

I do not think that nullfs-specific method is needed.
I already mailed the following patch to the reporters.

diff --git a/sys/fs/nullfs/null_vnops.c b/sys/fs/nullfs/null_vnops.c
index 5a6823f..38da43f 100644
--- a/sys/fs/nullfs/null_vnops.c
+++ b/sys/fs/nullfs/null_vnops.c
_at__at_ -742,5 +742,6 _at__at_ struct vop_vector null_vnodeops = {
 	.vop_setattr =		null_setattr,
 	.vop_strategy =		VOP_EOPNOTSUPP,
 	.vop_unlock =		null_unlock,
+	.vop_vptocnp =		vop_stdvptocnp,
 	.vop_vptofh =		null_vptofh,
 };