netdev - Re: [PATCH v2 net] net: enetc: survive memory pressure without crashing

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Date:   Thu, 27 Oct 2022 11:23:16 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 net] net: enetc: survive memory pressure without
 crashing

On Thu, 27 Oct 2022 18:02:09 +0000 Vladimir Oltean wrote:
> On Thu, Oct 27, 2022 at 10:58:24AM -0700, Jakub Kicinski wrote:
> > On Wed, 26 Oct 2022 15:13:30 +0300 Vladimir Oltean wrote:  
> > > To fix this problem, memset the DMA coherent area used for RX buffer
> > > descriptors in enetc_dma_alloc_bdr(). This makes all BDs be "not ready"
> > > by default, which makes enetc_clean_rx_ring() exit early from the BD
> > > processing loop when there is no valid buffer available.  
> > 
> > IIRC dma_alloc_coherent() always zeros, and I'd guess there is a cocci
> > script that checks this judging but the number of "fixes" we got for
> > this in the past.
> > 
> > scripts/coccinelle/api/alloc/zalloc-simple.cocci ?  
> 
> Yeah, ok, fair, I guess only the producer/consumer indices were the problem,
> then. The "junk" I was seeing in the buffer descriptors was the "Ready"
> bit caused by the hardware thinking it owns all BDs when in fact it
> owned none of them.
> 
> Is there a chance the patch makes it for this week's PR if I amend it
> really quick?

Yeah, you got 15min :)