[dpdk-dev] [PATCH dpdk-dev v3] mempool: sort the rte_mempool_ops by name

[Andrew Rybchenko]

On 3/7/20 3:51 PM, Andrew Rybchenko wrote:
> On 3/6/20 4:37 PM, Jerin Jacob wrote:
>> On Fri, Mar 6, 2020 at 7:06 PM <xiangxia.m.yue at gmail.com> wrote:
>>> From: Tonghao Zhang <xiangxia.m.yue at gmail.com>
>>>
>>> The order of mempool initiation affects mempool index in the
>>> rte_mempool_ops_table. For example, when building APPs with:
>>>
>>> $ gcc -lrte_mempool_bucket -lrte_mempool_ring ...
>>>
>>> The "bucket" mempool will be registered firstly, and its index
>>> in table is 0 while the index of "ring" mempool is 1. DPDK
>>> uses the mk/rte.app.mk to build APPs, and others, for example,
>>> Open vSwitch, use the libdpdk.a or libdpdk.so to build it.
>>> The mempool lib linked in dpdk and Open vSwitch is different.
>>>
>>> The mempool can be used between primary and secondary process,
>>> such as dpdk-pdump and pdump-pmd/Open vSwitch(pdump enabled).
>>> There will be a crash because dpdk-pdump creates the "ring_mp_mc"
>>> ring which index in table is 0, but the index of "bucket" ring
>>> is 0 in Open vSwitch. If Open vSwitch use the index 0 to get
>>> mempool ops and malloc memory from mempool. The crash will occur:
>>>
>>>      bucket_dequeue (access null and crash)
>>>      rte_mempool_get_ops (should get "ring_mp_mc",
>>>                           but get "bucket" mempool)
>>>      rte_mempool_ops_dequeue_bulk
>>>      ...
>>>      rte_pktmbuf_alloc
>>>      rte_pktmbuf_copy
>>>      pdump_copy
>>>      pdump_rx
>>>      rte_eth_rx_burst
>>>
>>> To avoid the crash, there are some solution:
>>> * constructor priority: Different mempool uses different
>>>    priority in RTE_INIT, but it's not easy to maintain.
>>>
>>> * change mk/rte.app.mk: Change the order in mk/rte.app.mk to
>>>    be same as libdpdk.a/libdpdk.so, but when adding a new mempool
>>>    driver in future, we must make sure the order.
>>>
>>> * register mempool orderly: Sort the mempool when registering,
>>>    so the lib linked will not affect the index in mempool table.
>>>
>>> Signed-off-by: Tonghao Zhang <xiangxia.m.yue at gmail.com>
>>> Acked-by: Olivier Matz <olivier.matz at 6wind.com>
>> Acked-by: Jerin Jacob <jerinj at marvell.com>
> 
> The patch is OK, but the fact that ops index changes during
> mempool driver lifetime is frightening. In fact it breaks
> rte_mempool_register_ops() return value semantics (read
> as API break). The return value is not used in DPDK, but it
> is a public function. If I'm not mistaken it should be taken
> into account.
> 
> Also I remember patches which warn about above behaviour
> in documentation. If behaviour changes, corresponding
> documentation must be updated.

One more point. If the patch is finally accepted it definitely
deserves few lines in release notes.