[fdborch] Fixed Orchagent crash in FDB flush on port disable.

[rajkumar38]

Signed-off-by: Rajkumar Pennadam Ramamoorthy [email protected]

What I did
Fixed Orchagent crash in FDB flush on port disable.
Steps to reproduce:

1. configure vlan and a port.
2. Learn MAC and populate FDB table.
3. Disable the port.

In fdborch.cpp:485, "m_entries" element is erased (from function "storeFdbEntryState") inside range based loop.
Iterators or references to erased element are invalidated. Hence update the iterator before removing the element.

Why I did it

How I verified it
Validate the above testcase with fix.

Details if related
Logs:

Using host libthread_db library "/lib/arm-linux-gnueabihf/libthread_db.so.1".
Core was generated by `/usr/bin/orchagent -d /var/log/swss -b 8192 -m 00:50:b6:50:51:51'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0 0xb6b5676c in std::local_Rb_tree_increment (__x=0x3633240a, __x@entry=0x69b2e0) at ../../../../../src/libstdc++-v3/src/c++98/tree.cc:65
65 ../../../../../src/libstdc++-v3/src/c++98/tree.cc: No such file or directory.
[Current thread is 1 (Thread 0xb6f69000 (LWP 44))]
(gdb) bt
#0 0xb6b5676c in std::local_Rb_tree_increment (__x=0x3633240a, __x@entry=0x69b2e0) at ../../../../../src/libstdc++-v3/src/c++98/tree.cc:65
#1 std::_Rb_tree_increment (__x=__x@entry=0x69b2e0) at ../../../../../src/libstdc++-v3/src/c++98/tree.cc:91
#2 0x004bfea0 in std::_Rb_tree_const_iterator::operator++ (this=) at /usr/include/c++/6/bits/stl_tree.h:288
#3 FdbOrch::update (this=this@entry=0x5ace68, type=, entry=, bridge_port_id=16325548649219474) at fdborch.cpp:235
#4 0x004c0746 in FdbOrch::doTask (this=0x5ace68, consumer=...) at fdborch.cpp:485
#5 0x004684a6 in OrchDaemon::start (this=0x59b57c) at orchdaemon.cpp:467
#6 0x00458e10 in main (argc=, argv=) at main.cpp:346
(gdb) p * __x
Cannot access memory at address 0x3633240a
(gdb) p __x
$1 = (std::_Rb_tree_node_base ) 0x3633240a
(gdb) fr 1
#1 std::_Rb_tree_increment (__x=__x@entry=0x69b2e0) at ../../../../../src/libstdc++-v3/src/c++98/tree.cc:91
91 in ../../../../../src/libstdc++-v3/src/c++98/tree.cc
(gdb) p __x
$2 = (const std::_Rb_tree_node_base ) 0x69b2e0
(gdb) p __x
$3 = {_M_color = (unknown: 11347552), _M_parent = 0xa0d3324, _M_left = 0xd4c4544, _M_right = 0x3633240a}
(gdb) p __x->_M_right
$4 = (std::_Rb_tree_node_base::_Base_ptr) 0x3633240a
(gdb) p __x->_M_right
Cannot access memory at address 0x3633240a
(gdb) p/x m_entries
$1 = std::set with 4159 elements = {[0] = {mac = {m_mac = {0x0, 0x0, 0x0, 0xaa, 0x11, 0x12}}, bv_id = 0x26000000000591, port_name = "Ethernet0"}, [1] = {

[rajkumar38]

@vasant17 @lguohan Pls review

[vasant17]

Looks good to me.
Just a suggestion, can we just update the for loop to the below, instead of increment iterator at multiple places?

for (auto itr = m_entries.begin(); itr != m_entries.end(); itr = next_item)
{
    auto next_item = std::next(itr, 1);
    .....
    ....
}

[rajkumar38]

Avoided multiple iterator increment. Updated patch. Pls check.