Date: Tue, 10 Sep 2002 23:58:02 -0700 (PDT) From: Don Lewis <dl-freebsd@catspoiler.org> To: current@FreeBSD.ORG, jeff@FreeBSD.ORG Subject: Re: nfs_inactive() bug? -> panic: lockmgr: locking against myself Message-ID: <200209110658.g8B6w2wr097059@gw.catspoiler.org> In-Reply-To: <200209110644.g8B6inwr097028@gw.catspoiler.org>
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On 10 Sep, Don Lewis wrote:
> It looks like the call to vrele() from vn_close() is executing the
> following code:
>
> if (vp->v_usecount == 1) {
> vp->v_usecount--;
> /*
> * We must call VOP_INACTIVE with the node locked.
> * If we are doing a vput, the node is already locked,
> * but, in the case of vrele, we must explicitly lock
> * the vnode before calling VOP_INACTIVE.
> */
> if (vn_lock(vp, LK_EXCLUSIVE | LK_INTERLOCK, td) == 0)
> VOP_INACTIVE(vp, td);
> VI_LOCK(vp);
> if (VSHOULDFREE(vp))
> vfree(vp);
> else
> vlruvp(vp);
> VI_UNLOCK(vp);
>
> It has decremented v_usecount to 0, grabbed an exclusive lock on the
> vnode, and has called VOP_INACTIVE().
> It looks like nfs_inactive() is executing the following code:
>
> if (sp) {
> /*
> * We need a reference to keep the vnode from being
> * recycled by getnewvnode while we do the I/O
> * associated with discarding the buffers unless we
> * are being forcibly unmounted in which case we already
> * have our own reference.
> */
> if (ap->a_vp->v_usecount > 0)
> (void) nfs_vinvalbuf(ap->a_vp, 0, sp->s_cred, td, 1);
> else if (vget(ap->a_vp, 0, td))
> panic("nfs_inactive: lost vnode");
> else {
> (void) nfs_vinvalbuf(ap->a_vp, 0, sp->s_cred, td, 1);
> vrele(ap->a_vp);
> }
>
A potentially better solution just occurred to me. It looks like it
would be better if vrele() waited to decrement v_usecount until *after*
the call to VOP_INACTIVE() (and after the call to VI_LOCK()). If that
were done, nfs_inactive() wouldn't need to muck with v_usecount at all.
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