netdev - RE: [PATCH] xen-netback: fix occasional leak of grant ref mappings under memory pressure

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Message-ID: <271c9beb91a74ded8e62d1cfc540976c@AMSPEX02CL02.citrite.net>
Date:   Thu, 28 Feb 2019 11:49:15 +0000
From:   Paul Durrant <Paul.Durrant@...rix.com>
To:     Igor Druzhinin <igor.druzhinin@...rix.com>,
        Wei Liu <wei.liu2@...rix.com>
CC:     "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>
Subject: RE: [PATCH] xen-netback: fix occasional leak of grant ref mappings
 under memory pressure

> -----Original Message-----
> From: Igor Druzhinin [mailto:igor.druzhinin@...rix.com]
> Sent: 28 February 2019 11:44
> To: Paul Durrant <Paul.Durrant@...rix.com>; Wei Liu <wei.liu2@...rix.com>
> Cc: xen-devel@...ts.xenproject.org; netdev@...r.kernel.org; linux-kernel@...r.kernel.org;
> davem@...emloft.net
> Subject: Re: [PATCH] xen-netback: fix occasional leak of grant ref mappings under memory pressure
> 
> On 28/02/2019 11:21, Paul Durrant wrote:
> >>> @@ -1153,6 +1152,10 @@ static int xenvif_tx_submit(struct xenvif_queue *queue)
> >>>                                 kfree_skb(skb);
> >>>                                 continue;
> >>>                         }
> >>> +
> >>> +                       /* Copied all the bits from the frag list. */
> >>> +                       skb_frag_list_init(skb);
> >>> +                       kfree(nskb);
> >>
> >> I think you want kfree_skb here?
> >
> > No. nskb is the frag list... it is unlinked from skb by the call to skb_frag_list_init() and then it
> can be freed on its own. The skb is what we need to retain, because that now contains all the data.
> >
> 
> Are you saying previous code in xenvif_handle_frag_list() incorrectly
> called kfree_skb()?

No, it correctly called kfree_skb() on nskb in the success case. What Wei and myself would prefer is that we have a single place that the frag list is freed in both the success and error cases.

  Paul

> 
> Igor