[Bug 1799397] Re: [dpdk]rte_memcpy() moves data incorrectly on Ubuntu 18.04 on Intel Skylake.
Christian Ehrhardt
1799397 at bugs.launchpad.net
Mon Nov 12 13:05:10 UTC 2018
Upstream bug is at https://bugs.dpdk.org/show_bug.cgi?id=97#c18
(Can't link it here :-/ )
They say:
- No crash seen with code generated by clang-6 or gcc-6, probably because they do not generate AVX512 instructions.
- Crash is confirmed with gcc-7 and gcc-8 when using AVX2 version of rte_memcpy.
Nobody tested the one in Disco yet, and I have no repro yet for my own.
Note: Really worth to read through all the info in that bug.
** Also affects: dpdk
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1799397
Title:
[dpdk]rte_memcpy() moves data incorrectly on Ubuntu 18.04 on Intel
Skylake.
Status in DPDK:
New
Status in dpdk package in Ubuntu:
Confirmed
Status in gcc-7 package in Ubuntu:
New
Bug description:
Hi, Christian
We've recently encountered a weird issue with Ubuntu 18.04 on the Skylake
server. I can always reproduce this crash and I could narrowed it down. I guess
it could be a GCC issue.
[1] How to reproduce
- ConnectX-4Lx/ConnectX-5 with mlx5 PMD in DPDK 18.02.1
- Ubuntu 18.04 on Intel Skylake server
- gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0
- Testpmd crashes when it starts to forward traffic. Easy to reproduce.
- Only happens on the Skylake server.
- DPDK 18.05 and later don't have such issue. git-bisect gives no clue.
This is because I enabled MEMPOOL_DEBUG and MLX5_DEBUG. As mempool/rte_memcpy is
inlined function, it should be affected. Now I can see the crash regardlessly -
18.02, 18.05 and 18.08.
[2] Failure point
The attached patch gives an insight of why it crashes. The following is the
result of the patch and the GDB commands.
In summary, rte_memcpy() doesn't work as expected. In __mempool_generic_put(),
there's rte_memcpy() to move the array of objects to the lcore cache. If I run
memcmp() right after rte_memcpy(dst, src, n), data in dst differs from data in
src. And it looks like some of data got shifted by a few bytes as you can see
below.
[GDB command]
$dst = 0x7ffff4e09ea8
$src = 0x7fffce3fb970
$n = 256
x/32gx 0x7ffff4e09ea8
x/32gx 0x7fffce3fb970
testpmd: /home/mlnxtest/dpdk/build/include/rte_mempool.h:1140: __mempool_generic_put: Assertion `0' failed.
Thread 4 "lcore-slave-1" received signal SIGABRT, Aborted.
[Switching to Thread 0x7fffce3ff700 (LWP 69913)]
(gdb) x/32gx 0x7ffff4e09ea8
0x7ffff4e09ea8: 0x00007fffaac38ec0 0x00007fffaac38500
0x7ffff4e09eb8: 0x00007fffaac37b40 0x00007fffaac37180
0x7ffff4e09ec8: 0x850000007fffaac3 0x7b4000007fffaac3
0x7ffff4e09ed8: 0x00007fffaac35440 0x00007fffaac34a80
0x7ffff4e09ee8: 0xaac3850000007fff 0xaac37b4000007fff
0x7ffff4e09ef8: 0x00007fffaac32d40 0x00007fffaac32380
0x7ffff4e09f08: 0x7fffaac385000000 0x7fffaac37b400000
0x7ffff4e09f18: 0x00007fffaac30640 0x00007fffaac2fc80
0x7ffff4e09f28: 0x00007fffaac2f2c0 0x00007fffaac2e900
0x7ffff4e09f38: 0x00007fffaac2df40 0x00007fffaac2d580
0x7ffff4e09f48: 0x00007fffaac2cbc0 0x00007fffaac2c200
0x7ffff4e09f58: 0x00007fffaac2b840 0x00007fffaac2ae80
0x7ffff4e09f68: 0x00007fffaac2a4c0 0x00007fffaac29b00
0x7ffff4e09f78: 0x00007fffaac29140 0x00007fffaac28780
0x7ffff4e09f88: 0x00007fffaac27dc0 0x00007fffaac27400
0x7ffff4e09f98: 0x00007fffaac26a40 0x00007fffaac26080
(gdb) x/32gx 0x7fffce3fb970
0x7fffce3fb970: 0x00007fffaac38ec0 0x00007fffaac38500
0x7fffce3fb980: 0x00007fffaac37b40 0x00007fffaac37180
0x7fffce3fb990: 0x00007fffaac367c0 0x00007fffaac35e00
0x7fffce3fb9a0: 0x00007fffaac35440 0x00007fffaac34a80
0x7fffce3fb9b0: 0x00007fffaac340c0 0x00007fffaac33700
0x7fffce3fb9c0: 0x00007fffaac32d40 0x00007fffaac32380
0x7fffce3fb9d0: 0x00007fffaac319c0 0x00007fffaac31000
0x7fffce3fb9e0: 0x00007fffaac30640 0x00007fffaac2fc80
0x7fffce3fb9f0: 0x00007fffaac2f2c0 0x00007fffaac2e900
0x7fffce3fba00: 0x00007fffaac2df40 0x00007fffaac2d580
0x7fffce3fba10: 0x00007fffaac2cbc0 0x00007fffaac2c200
0x7fffce3fba20: 0x00007fffaac2b840 0x00007fffaac2ae80
0x7fffce3fba30: 0x00007fffaac2a4c0 0x00007fffaac29b00
0x7fffce3fba40: 0x00007fffaac29140 0x00007fffaac28780
0x7fffce3fba50: 0x00007fffaac27dc0 0x00007fffaac27400
0x7fffce3fba60: 0x00007fffaac26a40 0x00007fffaac26080
AFAIK, AVX512F support is disabled by default in DPDK as it is still
experimental (CONFIG_RTE_ENABLE_AVX512=n). But with gcc optimization, AVX2
version of rte_memcpy() seems to be optimized with 512b instructions. If I
disable it by adding EXTRA_CFLAGS="-mno-avx512f", then it works fine and doesn't
crash.
Do you have any idea regarding this issue or are you already aware of
it?
Thanks,
Yongseok
$ git diff
diff --git a/config/common_base b/config/common_base
index ad03cf433..f512b5a88 100644
--- a/config/common_base
+++ b/config/common_base
@@ -275,8 +275,8 @@ CONFIG_RTE_LIBRTE_MLX4_TX_MP_CACHE=8
#
# Compile burst-oriented Mellanox ConnectX-4 & ConnectX-5 (MLX5) PMD
#
-CONFIG_RTE_LIBRTE_MLX5_PMD=n
-CONFIG_RTE_LIBRTE_MLX5_DEBUG=n
+CONFIG_RTE_LIBRTE_MLX5_PMD=y
+CONFIG_RTE_LIBRTE_MLX5_DEBUG=y
CONFIG_RTE_LIBRTE_MLX5_DLOPEN_DEPS=n
CONFIG_RTE_LIBRTE_MLX5_TX_MP_CACHE=8
@@ -597,7 +597,7 @@ CONFIG_RTE_RING_USE_C11_MEM_MODEL=n
#
CONFIG_RTE_LIBRTE_MEMPOOL=y
CONFIG_RTE_MEMPOOL_CACHE_MAX_SIZE=512
-CONFIG_RTE_LIBRTE_MEMPOOL_DEBUG=n
+CONFIG_RTE_LIBRTE_MEMPOOL_DEBUG=y
#
# Compile Mempool drivers
diff --git a/lib/librte_mempool/rte_mempool.h b/lib/librte_mempool/rte_mempool.h
index 8b1b7f7ed..9f48028d9 100644
--- a/lib/librte_mempool/rte_mempool.h
+++ b/lib/librte_mempool/rte_mempool.h
@@ -39,6 +39,7 @@
#include <errno.h>
#include <inttypes.h>
#include <sys/queue.h>
+#include <assert.h>
#include <rte_config.h>
#include <rte_spinlock.h>
@@ -1123,6 +1124,22 @@ __mempool_generic_put(struct rte_mempool *mp, void * const *obj_table,
/* Add elements back into the cache */
rte_memcpy(&cache_objs[0], obj_table, sizeof(void *) * n);
+ if(memcmp(&cache_objs[0], obj_table, sizeof(void *) * n)) {
+ printf("[GDB command] \n"
+ "$dst = %p\n"
+ "$src = %p\n"
+ "$n = %ld\n"
+ "x/%ldgx %p\n"
+ "x/%ldgx %p\n",
+ (void *)&cache_objs[0],
+ (const void *)obj_table,
+ sizeof(void *) * n,
+ sizeof(void *) * n / 8, (void *)&cache_objs[0],
+ sizeof(void *) * n / 8, (const void *)obj_table
+ );
+ assert(0);
+ }
+
cache->len += n;
if (cache->len >= cache->flushthresh) {
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