Enforce limit of 1000 open [uk]probes

The number of open probes has bitten users already, so lets enforce a
limit with a meaningful(ish) message.
Signed-off-by: Brenden Blanco <bblanco@plumgrid.com>

src/python/bcc/__init__.py

@@ -36,6 +36,7 @@ KALLSYMS = "/proc/kallsyms"
 ksym_addrs = []
 ksym_names = []
 ksym_loaded = 0
+_kprobe_limit = 1000
 
 @atexit.register
 def cleanup_kprobes():
@@ -54,6 +55,12 @@ def cleanup_kprobes():
     if tracefile:
         tracefile.close()
 
+
+def _check_probe_quota(num_new_probes):
+    if len(open_kprobes) + len(open_uprobes) + num_new_probes > _kprobe_limit:
+        raise Exception("Number of open probes would exceed quota")
+
+
 class BPF(object):
     SOCKET_FILTER = 1
     KPROBE = 2
@@ -282,8 +289,10 @@ class BPF(object):
         lines = p.communicate()[0].decode().split()
         with open("%s/../kprobes/blacklist" % TRACEFS) as f:
             blacklist = [line.split()[1] for line in f.readlines()]
-        return [line.rstrip() for line in lines if
+        fns = [line.rstrip() for line in lines if
                 (line != "\n" and line not in blacklist)]
+        _check_probe_quota(len(fns))
+        return fns
 
     def attach_kprobe(self, event="", fn_name="", event_re="",
             pid=-1, cpu=0, group_fd=-1):
@@ -298,6 +307,7 @@ class BPF(object):
                     pass
             return
 
+        _check_probe_quota(1)
         fn = self.load_func(fn_name, BPF.KPROBE)
         ev_name = "p_" + event.replace("+", "_").replace(".", "_")
         desc = "p:kprobes/%s %s" % (ev_name, event)
@@ -340,6 +350,7 @@ class BPF(object):
                     pass
             return
 
+        _check_probe_quota(1)
         fn = self.load_func(fn_name, BPF.KPROBE)
         ev_name = "r_" + event.replace("+", "_").replace(".", "_")
         desc = "r:kprobes/%s %s" % (ev_name, event)
@@ -463,6 +474,7 @@ class BPF(object):
 
         (path, addr) = BPF._check_path_symbol(name, sym, addr)
 
+        _check_probe_quota(1)
         fn = self.load_func(fn_name, BPF.KPROBE)
         ev_name = "p_%s_0x%x" % (self._probe_repl.sub("_", path), addr)
         desc = "p:uprobes/%s %s:0x%x" % (ev_name, path, addr)
@@ -506,6 +518,7 @@ class BPF(object):
 
         (path, addr) = BPF._check_path_symbol(name, sym, addr)
 
+        _check_probe_quota(1)
         fn = self.load_func(fn_name, BPF.KPROBE)
         ev_name = "r_%s_0x%x" % (self._probe_repl.sub("_", path), addr)
         desc = "r:uprobes/%s %s:0x%x" % (ev_name, path, addr)

tests/cc/test_probe_count.py

@@ -25,5 +25,15 @@ class TestKprobeCnt(TestCase):
         open_cnt = self.b.num_open_kprobes()
         self.assertEqual(actual_cnt, open_cnt)
 
+
+class TestProbeQuota(TestCase):
+    def setUp(self):
+        self.b = BPF(text="""int count(void *ctx) { return 0; }""")
+
+    def test_probe_quota(self):
+        with self.assertRaises(Exception):
+            self.b.attach_kprobe(event_re=".*", fn_name="count")
+
+
 if __name__ == "__main__":
     main()