nullfs: panic: vrele: negative ref cnt

[Paul B. Mahol]

On 3/9/09, John Baldwin <jhb at freebsd.org> 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().

It livelocks active vty into [ufs] state. Will try with WITNESS kernel soon.

load: 0.01  cmd: sh 1058 [ufs] 0.00u 0.02s 0% 1672k

> --- //depot/user/jhb/lock/fs/nullfs/null_vnops.c
> +++ /home/jhb/work/p4/lock/fs/nullfs/null_vnops.c
> @@ -722,6 +722,34 @@
>  	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
>   */
> @@ -743,4 +771,5 @@
>  	.vop_strategy =		VOP_EOPNOTSUPP,
>  	.vop_unlock =		null_unlock,
>  	.vop_vptofh =		null_vptofh,
> +	.vop_vptocnp =		null_vptocnp,
>  };
>
>
> --
> John Baldwin
>