Re: Broadcom bge(4) panics while shutting down

On Thu, May 14, 2009 at 5:37 PM, Xin LI <delphij_at_delphij.net> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> Hi, Alexander,
>
> Alexander Sack wrote:
> [...]
>>>> Preliminary testing shows no more panics start and stopping ports
>>>> under heavy load (panics were almost immediate otherwise).
>>>>
>>>> Thoughts?
>>> I think this would solve the problem but I'm not sure whether this would
>>> increase some overhead on the RX path.  It seems that there is a race
>>> between bge_release_resources() and bge_intr(), I mean, it might be a
>>> good idea to "drain" bge_intr() instead?
>>
>> Are you talking about detach time?  Because bge_stop() gets called
>> before bge_release_resources() and stops host interrupts so where is
>> the race again?  I mean at this point no more interrupts should be
>> delivered to bge_intr() (I can confirm from spec since BGE has
>> released it in the wild).  So why would you "drain" it at this
>> point....(the hardware is down including the firmware).
>>
>> I agree it adds a little overhead to the standard bge_rxeof() path
>> which I agree is very sensitive to change.  However, I think the check
>> at top is tolerable since the other recourse is crash.  I mean its
>> very easy to reproduce.  Flood a Broadcom card with traffic then stop
>> the card and let the race begin...it will go down in bge_rxeof() after
>> bge_stop releases the lock.
>>
>> I actually did not look at changing anything structurally to perhaps
>> make this whole predicament better but minimally there should be a
>> shield against this no?
>
> I'm all for a workaround at this point, but I really want to make sure
> that we are doing things in a safer manner if we can reach it timely.
>
> What about something like this, in my opinion, because bge_rxeof() would
> unlock sc in the middle, it would be probably better to re-check the
> IFF_DRV_RUNNING flag and avoid calling txeof after that (I've moved the
> condition to after we re-grab the lock to match the rest of the code:
>
> =====
> [delphij_at_charlie] /sys/dev/bge> svn diff -x -p
> Index: if_bge.c
> ===================================================================
> - --- if_bge.c  (revision 191995)
> +++ if_bge.c    (working copy)
> _at__at_ -3073,7 +3073,7 _at__at_ bge_rxeof(struct bge_softc *sc)
>                bus_dmamap_sync(sc->bge_cdata.bge_rx_jumbo_ring_tag,
>                    sc->bge_cdata.bge_rx_jumbo_ring_map, BUS_DMASYNC_POSTREAD);
>
> - -     while(sc->bge_rx_saved_considx !=
> +       while (sc->bge_rx_saved_considx !=
>            sc->bge_ldata.bge_status_block->bge_idx[0].bge_rx_prod_idx) {
>                struct bge_rx_bd        *cur_rx;
>                uint32_t                rxidx;
> _at__at_ -3193,6 +3193,9 _at__at_ bge_rxeof(struct bge_softc *sc)
>                BGE_UNLOCK(sc);
>                (*ifp->if_input)(ifp, m);
>                BGE_LOCK(sc);
> +
> +               if (!(ifp->if_drv_flags & IFF_DRV_RUNNING))
> +                       return;
>        }

Xin this looks fine by me, I actually put this up in the while loop as
I mentioned before which I think is functionality equivalent (can you
gain some optimizations by putting in the while loop though compiler
wise than a separate compilation unit?).

>        if (stdcnt > 0)
> _at__at_ -3301,6 +3304,10 _at__at_ bge_poll(struct ifnet *ifp, enum poll_cmd cmd, int
>
>        sc->rxcycles = count;
>        bge_rxeof(sc);
> +       if (!(ifp->if_drv_flags & IFF_DRV_RUNNING)) {
> +               BGE_UNLOCK(sc);
> +               return;
> +       }

So here if bge_rxeof() drops the lock, bge_stop() sneaks in reset flag
and doesn't bother to process txeof().  I can buy that.

>        bge_txeof(sc);
>        if (!IFQ_DRV_IS_EMPTY(&ifp->if_snd))
>                bge_start_locked(ifp);
> _at__at_ -3370,7 +3377,9 _at__at_ bge_intr(void *xsc)
>        if (ifp->if_drv_flags & IFF_DRV_RUNNING) {
>                /* Check RX return ring producer/consumer. */
>                bge_rxeof(sc);
> +       }
>
> +       if (ifp->if_drv_flags & IFF_DRV_RUNNING) {
>                /* Check TX ring producer/consumer. */
>                bge_txeof(sc);
>        }

Same here, avoid txeof() if bge_rxeof()/bge_stop() reset the
DRV_RUNNING flag.  Luckily txeof() doesn't drop the lock so no check
is needed in there.

I'm happier....should have thought about poll though (I hate polling).

-aps