netdev - Re: [PATCH net] xen-netback: Fix slot estimation

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Date:	Thu, 05 Jun 2014 15:02:09 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	zoltan.kiss@...rix.com
Cc:	xen-devel@...ts.xenproject.org, ian.campbell@...rix.com,
	wei.liu2@...rix.com, paul.durrant@...rix.com, linux@...elenboom.it,
	netdev@...r.kernel.org, david.vrabel@...rix.com
Subject: Re: [PATCH net] xen-netback: Fix slot estimation

From: Zoltan Kiss <zoltan.kiss@...rix.com>
Date: Tue, 3 Jun 2014 14:32:16 +0100

> A recent commit (a02eb4 "xen-netback: worse-case estimate in xenvif_rx_action is
> underestimating") capped the slot estimation to MAX_SKB_FRAGS, but that triggers
> the next BUG_ON a few lines down, as the packet consumes more slots than
> estimated.
> This patch remove that cap, and if the frontend doesn't provide enough slot,
> put back the skb to the top of the queue and caps rx_last_skb_slots. When the
> next try also fails, it drops the packet.
> Capping rx_last_skb_slots is needed because if the frontend never gives enough
> slots, the ring gets stalled.
> 
> Signed-off-by: Zoltan Kiss <zoltan.kiss@...rix.com>

Like David Laight, I do not like this patch at all.

Yes a crash or BUG_ON triggered is bad, but fixing it by deadlocking
TCP connections (a silent failure) is not an improvement.

I'm not applying this, sorry.
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