Date: Thu, 14 May 2009 16:01:33 -0400 From: Alexander Sack <pisymbol@gmail.com> To: freebsd-current@freebsd.org Subject: Re: Broadcom bge(4) panics while shutting down Message-ID: <3c0b01820905141301h1b08fc0ay1e6a1676b5a149d4@mail.gmail.com> In-Reply-To: <4A0C7544.6010304@delphij.net> References: <3c0b01820905141202w113966dp4bfbab73d84d585@mail.gmail.com> <4A0C7544.6010304@delphij.net>
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On Thu, May 14, 2009 at 3:47 PM, Xin LI <delphij@delphij.net> wrote:
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> Hi, Alexander,
>
> Alexander Sack wrote:
>> Hello:
>>
>> Under heavy traffic (100% utilization GIGE on a 2 port BGE card)
>> running BGE CURRENT driver I see panics on shutdown. =A0The reason is
>> because bge_rxeof() while processing its RX ring of BD's drops the
>> softc lock when it hands it off to its input function. =A0If bge_stop()
>> is waiting for it, it will then proceed to acquire lock and then
>> quiesce the hardware (reseting the card, clearing out BDs etc.). =A0Once
>> bge_stop() releases the softc lock, then bge_rxeof() under an
>> interrupt context (no polling here) will reacquire and continue to
>> process the ring which is a bad idea. =A0It should check to see if the
>> card is still running before continuing processing BDs (i.e. once
>> IF_DRV_RUNNING has been reset by bge_stop(), bge_rxeof() is done, bail
>> out).
>>
>> Here is my first go around with this patch:
>>
>>
>> -- if_bge.c.CURRENT =A0 2009-05-14 14:39:39.000000000 -0400
>> +++ if_bge.c =A02009-05-14 14:39:24.000000000 -0400
>> @@ -3081,6 +3081,10 @@
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 uint16_t =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0vlan=
_tag =3D 0;
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 int =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =
have_tag =3D 0;
>>
>> + =A0 =A0 =A0 =A0 =A0 =A0 if (!(ifp->if_drv_flags & IFF_DRV_RUNNING)) {
>> + =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 return;
>> + =A0 =A0 =A0 =A0 =A0 =A0 }
>> +
>> =A0#ifdef DEVICE_POLLING
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (ifp->if_capenable & IFCAP_POLLING) {
>> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 if (sc->rxcycles <=3D 0)
>>
>>
>> This prevents any panics during shutdown under heavy load and AS IT
>> TURNS out (I feel stupid for not looking) that em(4) already had this
>> check in its em_rxeof() function (right at the top of the loop). =A0I'm
>> more than happy changing it to the em style but above seems reasonable
>> to me though I have to verify there isn't anything missing off the
>> loop from a hardware standpoint (I don't think so because bge_stop()
>> did all the dirty work so I believe touching any registers after that
>> from bge_rxeof() is a bad idea).
>>
>> 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. =A0It 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?
-aps
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