perf tools: Fix crash with non-jited bpf progs

The addr in PERF_RECORD_KSYMBOL events for non-jited bpf progs points to
the bpf interpreter, ie. within kernel text section. When processing the
unregister event, this causes unexpected removal of vmlinux_map,
crashing perf later in cleanup:

  # perf record -- timeout --signal=INT 2s /usr/share/bcc/tools/execsnoop
  PCOMM            PID    PPID   RET ARGS
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.208 MB perf.data (5155 samples) ]
  perf: tools/include/linux/refcount.h:131: refcount_sub_and_test: Assertion `!(new > val)' failed.
  Aborted (core dumped)

  # perf script -D|grep KSYM
  0 0xa40 [0x48]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b530 len 0 type 1 flags 0x0 name bpf_prog_f958f6eb72ef5af6
  0 0xab0 [0x48]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b530 len 0 type 1 flags 0x0 name bpf_prog_8c42dee26e8cd4c2
  0 0xb20 [0x48]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b530 len 0 type 1 flags 0x0 name bpf_prog_f958f6eb72ef5af6
  108563691893 0x33d98 [0x58]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b3b0 len 0 type 1 flags 0x0 name bpf_prog_bc5697a410556fc2_syscall__execve
  108568518458 0x34098 [0x58]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b3f0 len 0 type 1 flags 0x0 name bpf_prog_45e2203c2928704d_do_ret_sys_execve
  109301967895 0x34830 [0x58]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b3b0 len 0 type 1 flags 0x1 name bpf_prog_bc5697a410556fc2_syscall__execve
  109302007356 0x348b0 [0x58]: PERF_RECORD_KSYMBOL addr ffffffffa9b6b3f0 len 0 type 1 flags 0x1 name bpf_prog_45e2203c2928704d_do_ret_sys_execve
  perf: tools/include/linux/refcount.h:131: refcount_sub_and_test: Assertion `!(new > val)' failed.

Here the addresses match the bpf interpreter:

  # grep -e ffffffffa9b6b530 -e ffffffffa9b6b3b0 -e ffffffffa9b6b3f0 /proc/kallsyms
  ffffffffa9b6b3b0 t __bpf_prog_run224
  ffffffffa9b6b3f0 t __bpf_prog_run192
  ffffffffa9b6b530 t __bpf_prog_run32

Fix by not allowing vmlinux_map to be removed by PERF_RECORD_KSYMBOL
unregister event.
Signed-off-by: Tommi Rantala <tommi.t.rantala@nokia.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Link: https://lore.kernel.org/r/20201016114718.54332-1-tommi.t.rantala@nokia.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/machine.c

@@ -786,11 +786,20 @@ static int machine__process_ksymbol_unregister(struct machine *machine,
 					       union perf_event *event,
 					       struct perf_sample *sample __maybe_unused)
 {
+	struct symbol *sym;
 	struct map *map;
 
 	map = maps__find(&machine->kmaps, event->ksymbol.addr);
-	if (map)
+	if (!map)
+		return 0;
+
+	if (map != machine->vmlinux_map)
 		maps__remove(&machine->kmaps, map);
+	else {
+		sym = dso__find_symbol(map->dso, map->map_ip(map, map->start));
+		if (sym)
+			dso__delete_symbol(map->dso, sym);
+	}
 
 	return 0;
 }

tools/perf/util/symbol.c

@@ -515,6 +515,13 @@ void dso__insert_symbol(struct dso *dso, struct symbol *sym)
 	}
 }
 
+void dso__delete_symbol(struct dso *dso, struct symbol *sym)
+{
+	rb_erase_cached(&sym->rb_node, &dso->symbols);
+	symbol__delete(sym);
+	dso__reset_find_symbol_cache(dso);
+}
+
 struct symbol *dso__find_symbol(struct dso *dso, u64 addr)
 {
 	if (dso->last_find_result.addr != addr || dso->last_find_result.symbol == NULL) {

tools/perf/util/symbol.h

@@ -131,6 +131,8 @@ int dso__load_kallsyms(struct dso *dso, const char *filename, struct map *map);
 
 void dso__insert_symbol(struct dso *dso,
 			struct symbol *sym);
+void dso__delete_symbol(struct dso *dso,
+			struct symbol *sym);
 
 struct symbol *dso__find_symbol(struct dso *dso, u64 addr);
 struct symbol *dso__find_symbol_by_name(struct dso *dso, const char *name);