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To: Gage Eads <gage.eads@intel.com>, <dev@dpdk.org>
CC: <olivier.matz@6wind.com>, <stable@dpdk.org>
References: <20190618184830.29110-1-gage.eads@intel.com>
From: Andrew Rybchenko <arybchenko@solarflare.com>
Message-ID: <381b4578-891f-5b1a-f2c4-38d73360f5d7@solarflare.com>
Date: Thu, 20 Jun 2019 21:01:29 +0300
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Subject: Re: [dpdk-dev] [PATCH] doc: add multi-proc shared lib mempool note
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On 6/18/19 9:48 PM, Gage Eads wrote:
> The mempool library assigns handler ops indexes based on the dynamic load
> order of mempool handlers. Indexes are used so a mempool can be used by
> multiple processes, but this only works if all processes agree on the
> mapping from index to mempool handler.
>
> When using the '-d' argument, it's possible for different processes to load
> mempool handlers in different orders, and thus have different
> index->handler mappings. Using a mempool in multiple of such processes will
> result in undefined behavior.
>
> This commit adds a note to the mempool library programmer's guide warning
> users against this.
>
> Fixes: 449c49b93a6b ("mempool: support handler operations")
> Cc: stable@dpdk.org
>
> Signed-off-by: Gage Eads <gage.eads@intel.com>
> ---
> doc/guides/prog_guide/mempool_lib.rst | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/doc/guides/prog_guide/mempool_lib.rst b/doc/guides/prog_guide/mempool_lib.rst
> index 52a569f57..4470f6b38 100644
> --- a/doc/guides/prog_guide/mempool_lib.rst
> +++ b/doc/guides/prog_guide/mempool_lib.rst
> @@ -133,6 +133,13 @@ For applications that use ``rte_pktmbuf_create()``, there is a config setting
> (``RTE_MBUF_DEFAULT_MEMPOOL_OPS``) that allows the application to make use of
> an alternative mempool handler.
>
> + .. note::
> +
> + When running a DPDK application with shared libraries, mempool handler
> + shared objects specified with the '-d' EAL command-line parameter are
> + dynamically loaded. When running a multi-process application with shared
> + libraries, the -d arguments for mempool handlers *must be specified in the
> + same order for all processes* to ensure correct operation.
>
One more empty line is required here, other than that:
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
I think it is OK as a fix for stable branches.
In theory I think it is still technically possible to guarantee ops
indices correctness
using dedicated memzone (as Olivier suggested), but with sync up on
rte_mempool_{get,set}_ops() (which should be called when EAL is
initialized) and
reordering. However, it requires API breakage to avoid returning of
ops_index
on register (since it may change in secondary process on resync when EAL is
already initialized).