Date: Mon, 2 Apr 2012 08:35:00 -0400 From: John Baldwin <jhb@freebsd.org> To: freebsd-net@freebsd.org Cc: Andrew Boyer <aboyer@averesystems.com> Subject: Re: LACP kernel panics: /* unlocking is safe here */ Message-ID: <201204020835.00357.jhb@freebsd.org> In-Reply-To: <D02B1265-C1F4-4F6A-979D-E141565E813F@averesystems.com> References: <D02B1265-C1F4-4F6A-979D-E141565E813F@averesystems.com>
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On Friday, March 30, 2012 6:04:24 pm Andrew Boyer wrote:
> While investigating a LACP issue, I turned on LACP_DEBUG on a debug kernel.
In this configuration it's easy to panic the kernel - just run 'ifconfig lagg0
laggproto lacp' on a lagg that's already in LACP mode and receiving LACP
messages.
>
> The problem is that lagg_lacp_detach() drops the lagg wlock (with the
comment in the title), which allows incoming LACP messages to get through
lagg_input() while the structure is being destroyed in lacp_detach().
>
> There's a very simple fix, but I don't know if it's the best way to fix it.
Resetting the protocol before calling sc_detach causes any further incoming
packets to be dropped until the lagg gets reconfigured. Thoughts?
This looks sensible.
> Is it safe to just hold on to the lagg wlock across the callout_drain()
calls in lacp_detach()? That's what OpenBSD does.
No, callout_drain() can sleep. Also, if this is using callout_init_mtx()
or callout_init_rwlock() (which it probably should), then holding the
lock across callout_drain() could deadlock.
> -Andrew
>
> Index: sys/net/if_lagg.c
> ===================================================================
> --- sys/net/if_lagg.c (revision 233707)
> +++ sys/net/if_lagg.c (working copy)
> @@ -952,9 +952,10 @@
> }
> if (sc->sc_proto != LAGG_PROTO_NONE) {
> LAGG_WLOCK(sc);
> + /* Reset protocol */
> + sc->sc_proto = LAGG_PROTO_NONE;
> error = sc->sc_detach(sc);
> - /* Reset protocol and pointers */
> - sc->sc_proto = LAGG_PROTO_NONE;
> + /* Reset pointers */
> sc->sc_detach = NULL;
> sc->sc_start = NULL;
> sc->sc_input = NULL;
>
> --------------------------------------------------
> Andrew Boyer aboyer@averesystems.com
>
>
>
>
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--
John Baldwin
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