Dear Net-Snmp Team,
We are making use of Net-Snmp library 5.4.1 for embedded development where in
we are facing one challenge which I would like to share with you.
In order to make snmp work,we have created one thread in which we have called
agent_check_and_process() with non-blocking mode.We also use
agent_check_and_proces() in other process, not in same process.
Code snippet
==========
static void snmp_request_daemon(void *arg)
{
int pcount;
AC_MU_ERROR m_err;
for (;;) {
m_err = ac_mu_lock(daemon_guard, AC_MU_WAIT, 100);
if (m_err == AC_MU_SUCCESS) {
pcount = agent_check_and_process(0);
if (pcount > 0) {
aci_msg(("handled %d snmp packets", pcount));
}
ac_mu_unlock(daemon_guard);
ac_t_sleep(10);
}
}
}
Problem
======
However the call agent_check_process() is getting struck at snmp_read for some
reason. Since snmp_read is holding snmp_res_lock and not returning back, all
other snmp calls (Ex snmp_close()) is blocked on snmp_res_lock. It leads to a
lockup.
backtrace at the time of lockup.
=======================
1. Thread struck at snmp_read()
2ab63638 recvmsg+0x80
2c2280cc netsnmp_udp_recv+0x138
2c1f0b54 _sess_read+0x118
2c1f1d58 snmp_sess_read+0x2C
2c1f1e00 snmp_read+0x64 (Struck at snmp_read. It is
waiting to get packets by holding snmp_res_lock)
2c0ee3fc agent_check_and_process+0xD4
005b1090 snmp_request_daemon+0x4C
2ab0e464 wrapperThread+0x168
2ab5985c start_thread+0x90
2c409e98 __thread_start+0x28 (dp-bit.c)
2. Thread waiting for the lock.
2ab6177c sem_wait@GLIBC_2.0+0x12C
2c21de4c snmp_res_lock+0x138
2c1e2be4 snmp_close+0x34 (Snmp_close is waiting for the
snmp_res_lock).
005adbc8 ac_snmp_get+0x8CC
I would be pleased if you could help me in understanding the reason for
snmp_read to get blocked.Thanks for listening and reading. I am expecting the
soon reply from your fantastic team.
Thanks
Jegan
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