selftests: tc-testing: timeout on unbounded loops

In the spirit of failing early, timeout on unbounded loops that take
longer than 20 ticks to complete. Such loops are to ensure that objects
created are already visible so tests can proceed without any issues.

If a test setup takes more than 20 ticks to see an object, there's
definetely something wrong.
Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Link: https://lore.kernel.org/r/20231117171208.2066136-6-pctammela@mojatatu.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/testing/selftests/tc-testing/plugin-lib/nsPlugin.py

@@ -40,7 +40,10 @@ class SubPlugin(TdcPlugin):
             self._ns_create()
 
         # Make sure the netns is visible in the fs
+        ticks = 20
         while True:
+            if ticks == 0:
+                raise TimeoutError
             self._proc_check()
             try:
                 ns = self.args.NAMES['NS']
@@ -49,6 +52,7 @@ class SubPlugin(TdcPlugin):
                 break
             except:
                 time.sleep(0.1)
+                ticks -= 1
                 continue
 
     def pre_case(self, test, test_skip):
@@ -127,7 +131,10 @@ class SubPlugin(TdcPlugin):
         with IPRoute() as ip:
             ip.link('add', ifname=dev1, kind='veth', peer={'ifname': dev0, 'net_ns_fd':'/proc/1/ns/net'})
             ip.link('add', ifname=dummy, kind='dummy')
+            ticks = 20
             while True:
+                if ticks == 0:
+                    raise TimeoutError
                 try:
                     dev1_idx = ip.link_lookup(ifname=dev1)[0]
                     dummy_idx = ip.link_lookup(ifname=dummy)[0]
@@ -136,17 +143,22 @@ class SubPlugin(TdcPlugin):
                     break
                 except:
                     time.sleep(0.1)
+                    ticks -= 1
                     continue
         netns.popns()
 
         with IPRoute() as ip:
+            ticks = 20
             while True:
+                if ticks == 0:
+                    raise TimeoutError
                 try:
                     dev0_idx = ip.link_lookup(ifname=dev0)[0]
                     ip.link('set', index=dev0_idx, state='up')
                     break
                 except:
                     time.sleep(0.1)
+                    ticks -= 1
                     continue
 
     def _ns_create_cmds(self):