From: Yuanhan Liu <yuanhan.liu@linux.intel.com>
To: dev@dpdk.org
Cc: Maxime Coquelin <maxime.coquelin@redhat.com>, stable@dpdk.org
Subject: Re: [dpdk-stable] [PATCH] vhost: fix dequeue zero copy
Date: Wed, 19 Apr 2017 16:43:10 +0800 [thread overview]
Message-ID: <20170419084310.GD31523@yliu-dev.sh.intel.com> (raw)
In-Reply-To: <1492579561-19619-1-git-send-email-yuanhan.liu@linux.intel.com>
On Wed, Apr 19, 2017 at 01:26:01PM +0800, Yuanhan Liu wrote:
> For zero copy mode, we need pin the mbuf to not let the underlaying PMD
> driver (or the app) free the mbuf. Currently, only the heading mbuf is
> pinned. However, the mbuf free function would try to free all mbufs
> in the mbuf chain (-1 to the refcnt). This may lead the head mbuf being
> still pinned, while the other subsequent mbufs are actually freed. Which
> is wrong.
>
> It becomes more fatal after the mbuf refactor, more specificly, after
> the commit 8f094a9ac5d7 ("mbuf: set mbuf fields while in pool"). The
> refcnt resets to 1 after the last real reference. OTOH, it leads to a
> situtation that we never know one mbuf is actually freed or not. This
> would result the mbuf __just__ after the heading mbuf being freed twice:
> it's firstly freed (and put back to mempool) when the underlaying PMD
> finishes the DMA. Later, it will then be freed again when vhost unpins
> it. Meaning, one mbuf may be returned to the mempool twice, while in
> turn, being allocated twice later. Something uncertain may happen then.
> For example, the VM2VM case becomes broken.
>
> Fixes: b0a985d1f340 ("vhost: add dequeue zero copy")
>
> Cc: stable@dpdk.org
> Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Applied to dpdk-next-virtio.
--yliu
prev parent reply other threads:[~2017-04-19 8:46 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-19 5:26 Yuanhan Liu
2017-04-19 8:43 ` Yuanhan Liu [this message]
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