segmentation fault when using a non NULL pointer - c

Question

there is a weird problem as title when using dpdk,
When I use rte_pktmbuf_alloc(struct rte_mempool *) and already verify the return value of rte_pktmbuf_pool_create() is not NULL, the process receive segmentation fault.
Follow
ing message is output of gdb in dpdk source code:
Thread 1 "osw" received signal SIGSEGV, Segmentation fault.
0x00000000005e9f41 in __mempool_generic_get (cache=0x1a7dfc000000000, n=1, obj_table=0x7fffffffdec8, mp=0x101a7df00)at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1449
1449 if (unlikely(cache == NULL || n >= cache->size))
(gdb) p cache
$1 = (struct rte_mempool_cache *) 0x1a7dfc000000000
(gdb) bt
0 0x00000000005e9f41 in __mempool_generic_get (cache=0x1a7dfc000000000, n=1, obj_table=0x7fffffffdeb8, mp=0x101a7df00)
at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1449
1 rte_mempool_generic_get (cache=0x1a7dfc000000000, n=1, obj_table=0x7fffffffdeb8, mp=0x101a7df00)
at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1517
2 rte_mempool_get_bulk (n=1, obj_table=0x7fffffffdeb8, mp=0x101a7df00)
at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1552
3 rte_mempool_get (obj_p=0x7fffffffdeb8, mp=0x101a7df00) at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1578
4 rte_mbuf_raw_alloc (mp=0x101a7df00) at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mbuf.h:586
5 rte_pktmbuf_alloc (mp=0x101a7df00) at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mbuf.h:896
And I dig into rte_mempool.h:
and change line 1449-1450
1449 if (unlikely(cache == NULL || n >= cache->size))
1450 goto ring_dequeue;
to
1449 if (unlikely(cache == NULL))
1450 goto ring_dequeue;
1451 if (unlikely(n >= cache->size))
1452 goto ring_dequeue;
and it also fail at line 1451
the gdb output message after changing:
Thread 1 "osw" received signal SIGSEGV, Segmentation fault.
__mempool_generic_get (cache=0x1a7dfc000000000, n=1, obj_table=0x7fffffffdeb8, mp=0x101a7df00)
at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1451
1451 if (unlikely(n >= cache->size))
(gdb) p cache
$1 = (struct rte_mempool_cache *) 0x1a7dfc000000000
(gdb) bt
0 __mempool_generic_get (cache=0x1a7dfc000000000, n=1, obj_table=0x7fffffffdeb8, mp=0x101a7df00)
at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1451
1 rte_mempool_generic_get (cache=0x1a7dfc000000000, n=1, obj_table=0x7fffffffdeb8, mp=0x101a7df00)
at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1519
2 rte_mempool_get_bulk (n=1, obj_table=0x7fffffffdeb8, mp=0x101a7df00)
at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1554
3 rte_mempool_get (obj_p=0x7fffffffdeb8, mp=0x101a7df00) at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mempool.h:1580
4 rte_mbuf_raw_alloc (mp=0x101a7df00) at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mbuf.h:586
5 rte_pktmbuf_alloc (mp=0x101a7df00) at /root/dpdk-20.05/x86_64-native-linuxapp-gcc/include/rte_mbuf.h:896
6 main (argc=<optimized out>, argv=<optimized out>) at ofpd.c:150
(gdb) p cache->size
Cannot access memory at address 0x1a7dfc000000000
It looks like the memory address “cache” pointer stored is not NULL but it actually is a NULL pointer.
I have no idea that why does the "cache" pointer address be non zero at prefix 4 bytes and zero at postfix 4 bytes.
The DPDK version is 20.05, I also tried 18.11 and 19.11.
OS is CentOS 8.1 kernel is 4.18.0-147.el8.x86_64.
CPU is AMD EPYC 7401P.
#define RING_SIZE 16384
#define NUM_MBUFS 8191
#define MBUF_CACHE_SIZE 512
int main(int argc, char **argv)
{
int ret;
uint16_t portid;
unsigned cpu_id = 1;
struct rte_mempool *tmp;
int arg = rte_eal_init(argc, argv);
if (arg < 0)
rte_exit(EXIT_FAILURE, "Cannot init EAL: %s\n", rte_strerror(rte_errno));
if (rte_lcore_count() < 10)
rte_exit(EXIT_FAILURE, "We need at least 10 cores.\n");
argc -= arg;
argv += arg;
/* Creates a new mempool in memory to hold the mbufs. */
tmp = rte_pktmbuf_pool_create("TMP", NUM_MBUFS, MBUF_CACHE_SIZE, 0, RTE_MBUF_DEFAULT_BUF_SIZE, rte_socket_id());
if (tmp == NULL)
rte_exit(EXIT_FAILURE, "Cannot create mbuf pool, %s\n", rte_strerror(rte_errno));
printf("tmp addr = %x\n", tmp);
struct rte_mbuf *test = rte_pktmbuf_alloc(tmp);
rte_exit(EXIT_FAILURE, "end\n");
}
I have ever faced same problem when using the return pointer of getifaddrs(), it also got segmentation fault, I had to shift the pointer address like
ifa->ifa_addr = (struct sockaddr *)((uintptr_t)(ifa->ifa_addr) >> 32);
and then it can work normally.
Thereforer, I think this is not dpdk specific issue.
Does anyone know this issue?
Thanks.

Answer 1

I am able to run this without any error by modifying your code for
include headers
removed unused variables
add check if the returned value is NULL or not for alloc
Test on:
CPU: Intel(R) Xeon(R) CPU E5-2699
OS: 4.15.0-101-generic
GCC: 7.5.0
DPDK version: 19.11.2, dpdk mainline
Library mode: static
code:
int main(int argc, char **argv)
{
int ret = 0;
struct rte_mempool *tmp;
int arg = rte_eal_init(argc, argv);
if (arg < 0)
rte_exit(EXIT_FAILURE, "Cannot init EAL: %s\n", rte_strerror(rte_errno));
if (rte_lcore_count() < 10)
rte_exit(EXIT_FAILURE, "We need at least 10 cores.\n");
argc -= arg;
argv += arg;
/* Creates a new mempool in memory to hold the mbufs. */
tmp = rte_pktmbuf_pool_create("TMP", NUM_MBUFS, MBUF_CACHE_SIZE, 0, RTE_MBUF_DEFAULT_BUF_SIZE, rte_socket_id());
if (tmp == NULL)
rte_exit(EXIT_FAILURE, "Cannot create mbuf pool, %s\n", rte_strerror(rte_errno));
printf("tmp addr = %p\n", tmp);
struct rte_mbuf *test = rte_pktmbuf_alloc(tmp);
if (test == NULL)
rte_exit(EXIT_FAILURE, "end\n");
return ret;
}
[EDIT-1] based on the comment Brydon Gibson
Note:
As I do not have access to your codebase or working code snippet my suggestion is to lookup any example code from DPDK/examples/l2fwd or DPDK/examples/skeleton and copy the headers for your compilation.
I assume both the author THE and Brydon are different individuals and might be facing similar on the different code bases.
current question claims with DPDK version 20.05, 18.11 and 19.11 the error is reproduced with code snippet.
current answer clearly sates with static linking of the library the same code snippet works
Requested #BrydonGibson to open the ticket with relevant information and environment details as it might be different.