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

[Tonghao Zhang <xiangxia.m.yue@gmail.com>]

On Sat, Mar 7, 2020 at 8:54 PM Andrew Rybchenko
<arybchenko@solarflare.com> wrote:
>
> 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@gmail.com> wrote:
> >>> From: Tonghao Zhang <xiangxia.m.yue@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@gmail.com>
> >>> Acked-by: Olivier Matz <olivier.matz@6wind.com>
> >> Acked-by: Jerin Jacob <jerinj@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.
Yes, should update the doc: how about this:

diff --git a/lib/librte_mempool/rte_mempool.h b/lib/librte_mempool/rte_mempool.h
index c90cf31..5a9c8a7 100644
--- a/lib/librte_mempool/rte_mempool.h
+++ b/lib/librte_mempool/rte_mempool.h
@@ -904,7 +904,9 @@ int rte_mempool_ops_get_info(const struct rte_mempool *mp,
  * @param ops
  *   Pointer to an ops structure to register.
  * @return
- *   - >=0: Success; return the index of the ops struct in the table.
+ *   - >=0: Success; return the index of the last ops struct in the table.
+ *          The number of the ops struct registered is equal to index
+ *          returned + 1.
  *   - -EINVAL - some missing callbacks while registering ops struct.
  *   - -ENOSPC - the maximum number of ops structs has been reached.
  */
diff --git a/lib/librte_mempool/rte_mempool_ops.c
b/lib/librte_mempool/rte_mempool_ops.c
index b0da096..053f340 100644
--- a/lib/librte_mempool/rte_mempool_ops.c
+++ b/lib/librte_mempool/rte_mempool_ops.c
@@ -26,7 +26,11 @@ struct rte_mempool_ops_table rte_mempool_ops_table = {
        return strcmp(m_a->name, m_b->name);
 }

-/* add a new ops struct in rte_mempool_ops_table, return its index. */
+/*
+ * add a new ops struct in rte_mempool_ops_table.
+ * on success, return the index of the last ops
+ * struct in the table.
+ */
 int
 rte_mempool_register_ops(const struct rte_mempool_ops *h)
 {
> > 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.
OK, a separate patch should be sent before DPDK 20.05 release ?
>


-- 
Thanks,
Tonghao