Re: Kernel panic: kernel diagnostic assertion "/usr/ "sc-ysc_tx_avail > used" failed: file src/sys/dev/pv/if_xnf.c", line 642

On Sun, May 03, 2026 at 02:46:55PM +0200, Stefan Sperling wrote:
> On Wed, Dec 17, 2025 at 03:44:22PM +0100, Stefan Sperling wrote:
> > On Wed, Dec 17, 2025 at 03:37:56PM +0100, Stefan Sperling wrote:
> > > +	if (frags > sc->sc_tx_frags || frags > sc->sc_tx_avail) {
> > 
> > Perhaps this must check frags >= sc->sc_tx_avail to prevent the assertion
> > failure in all cases.
>  
> I still have not heard from anyone about this fix. I do not use xnf myself
> and I lack a test setup for it. I will drop this diff from my pending
> queue soon if I don't hear anything.
> 
> And I would need an OK from another developer to commit it.

I started reworking xnf to manage ring space like other drivers,
but I haven't got it working yet.  This looks like a good fix for
the current code, and it survives some basic testing.
ok jmatthew@


> 
> Context: https://marc.info/?l=openbsd-bugs&m=176598512119200&w=2
> 
> commit - 179a5728e367b8eca388e404a7fbcc08b887b86c
> blob - 3c423aee2e37c66eb446889acb80c2dd19a4648a
> file + sys/dev/pv/if_xnf.c
> --- sys/dev/pv/if_xnf.c
> +++ sys/dev/pv/if_xnf.c
> @@ -564,11 +564,13 @@ xnf_encap(struct xnf_softc *sc, struct mbuf *m_head, u
>  	struct mbuf *m, **next;
>  	uint32_t oprod = *prod;
>  	uint16_t id;
> -	int i, flags, n, used = 0;
> +	int i, flags, n, used = 0, frags;
>  
> -	if ((xnf_fragcount(m_head) > sc->sc_tx_frags) &&
> -	    m_defrag(m_head, M_DONTWAIT))
> -		return (ENOBUFS);
> +	frags = xnf_fragcount(m_head);
> +	if (frags > sc->sc_tx_frags || frags >= sc->sc_tx_avail) {
> +		if (m_defrag(m_head, M_DONTWAIT))
> +			return (ENOBUFS);
> +	}
>  
>  	flags = (sc->sc_domid << 16) | BUS_DMA_WRITE | BUS_DMA_NOWAIT;
>  
>