netdev - Re: [PATCH] virtio_net: indicate oom when addbuf returns failure

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Date:	Mon, 7 Jun 2010 08:24:41 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>, stable@...nel.org,
	Bruce Rogers <brogers@...ell.com>, netdev@...r.kernel.org,
	virtualization@...ts.linux-foundation.org,
	Shirley Ma <mashirle@...ibm.com>
Subject: Re: [PATCH] virtio_net: indicate oom when addbuf returns failure

On Sun, Jun 06, 2010 at 11:13:00PM +0300, Michael S. Tsirkin wrote:
>
> Actually this code looks strange:
> Note that add_buf inicates out of memory
> condition with a positive return value, and ring full
> (which is not an error!) with -ENOSPC.

Indeed, this ultimately came from

commit 9ab86bbcf8be755256f0a5e994e0b38af6b4d399
Author: Shirley Ma <mashirle@...ibm.com>
Date:   Fri Jan 29 03:20:04 2010 +0000

    virtio_net: Defer skb allocation in receive path Date: Wed, 13 Jan 2010 12:53:38 -0800

(Greg, please don't apply this even though I've just given you
the upstream commit ID that you were asking for :)

where it confuses a memory allocation error with an add_buf failure.

> Possibly the right thing to do is to
> 1. handle ENOMEM specially
> 2. fix add_buf to return ENOMEM on error

I think we should make it so that only a memory allocation error
is returned as before.  There is no need for returning the add_buf
error unless add_buf is now doing an allocation itself that needs
to be retried.

Thanks,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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