netdev - RE: [PATCH] bnx2x: fix panic when TX ring is full

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Message-ID: <504C9EFCA2D0054393414C9CB605C37F1CF19E@SJEXCHMB06.corp.ad.broadcom.com>
Date:	Sat, 16 Jun 2012 07:40:29 +0000
From:	"Dmitry Kravkov" <dmitry@...adcom.com>
To:	"'David Miller'" <davem@...emloft.net>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>
cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"therbert@...gle.com" <therbert@...gle.com>,
	"evansr@...gle.com" <evansr@...gle.com>,
	"Eilon Greenstein" <eilong@...adcom.com>,
	"Merav Sicron" <meravs@...adcom.com>,
	"Yaniv Rosner" <yaniv.rosner@...adcom.com>,
	"willemb@...gle.com" <willemb@...gle.com>,
	"thruby@...gle.com" <thruby@...gle.com>
Subject: RE: [PATCH] bnx2x: fix panic when TX ring is full

Hi Eric and Tomas

> From: netdev-owner@...r.kernel.org [mailto:netdev-
> owner@...r.kernel.org] On Behalf Of David Miller
> Sent: Saturday, June 16, 2012 1:31 AM
> To: eric.dumazet@...il.com
> Cc: netdev@...r.kernel.org; therbert@...gle.com; evansr@...gle.com;
> Eilon Greenstein; Merav Sicron; Yaniv Rosner; willemb@...gle.com;
> thruby@...gle.com
> Subject: Re: [PATCH] bnx2x: fix panic when TX ring is full
> 
> From: Eric Dumazet <eric.dumazet@...il.com>
> Date: Wed, 13 Jun 2012 21:45:16 +0200
> 
> > From: Eric Dumazet <edumazet@...gle.com>
> >
> > There is a off by one error in the minimal number of BD in
> > bnx2x_start_xmit() and bnx2x_tx_int() before stopping/resuming tx
> queue.
> >
> > A full size GSO packet, with data included in skb->head really needs
> > (MAX_SKB_FRAGS + 4) BDs, because of bnx2x_tx_split()
> >
> > This error triggers if BQL is disabled and heavy TCP transmit traffic
> > occurs.
> >
> > bnx2x_tx_split() definitely can be called, remove a wrong comment.
> >
> > Reported-by: Tomas Hruby <thruby@...gle.com>
> > Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Theoretically a can't see how we can reach the case with 4 BDs required apart of frags,
Usually we need 2, when split invoked 3:
1.Start
2.Start(split)
3.Parsing
+ Frags

Next pages descriptors and 2 extras for full indication are not counted as available.

Practically I'm running the traffic for more then a day without hitting the panic.

Can you describe the scenario you reproduced this in details? And which code has paniced? 

Thanks
 
> I got tired of waiting for the Broadcom "maintainers" to review this, so I just
> applied it to 'net', thanks Eric.



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