perf kvm: Fix segfault with report and mixed guestmount use

Using the guestmount option on record:
    $ perf kvm --guest --host --guestmount=/tmp/guest-mount record -ag

But not the subsequent report:
    $ perf kvm report

causes a SEGFAULT in the usual place:
(gdb) bt
0  0x0000000000470356 in machine__mmap_name (self=0x0, bf=0x7fffffffbdb0 " z\370\367\377\177", size=
    4096) at util/map.c:712
1  0x00000000004453e8 in perf_event__process_kernel_mmap (tool=0x7fffffffde10, event=0x7ffff7f87e38,
    machine=0x0) at util/event.c:550
2  0x00000000004458c9 in perf_event__process_mmap (tool=0x7fffffffde10, event=0x7ffff7f87e38, sample=
    0x7fffffffd2a0, machine=0x0) at util/event.c:656
3  0x00000000004733e0 in perf_session_deliver_event (session=0x91aca0, event=0x7ffff7f87e38, sample=
    0x7fffffffd2a0, tool=0x7fffffffde10, file_offset=7736) at util/session.c:979
...

The MMAP events in this case already contain the full path to the
module. No need to require it for the report path to.

Signed-off-by: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1341241977-71535-1-git-send-email-dsahern@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/map.c

@@ -669,24 +669,25 @@ struct machine *machines__find(struct rb_root *self, pid_t pid)
 struct machine *machines__findnew(struct rb_root *self, pid_t pid)
 {
 	char path[PATH_MAX];
-	const char *root_dir;
+	const char *root_dir = "";
 	struct machine *machine = machines__find(self, pid);
 
-	if (!machine || machine->pid != pid) {
-		if (pid == HOST_KERNEL_ID || pid == DEFAULT_GUEST_KERNEL_ID)
-			root_dir = "";
-		else {
-			if (!symbol_conf.guestmount)
+	if (machine && (machine->pid == pid))
 		goto out;
+
+	if ((pid != HOST_KERNEL_ID) &&
+	    (pid != DEFAULT_GUEST_KERNEL_ID) &&
+	    (symbol_conf.guestmount)) {
 		sprintf(path, "%s/%d", symbol_conf.guestmount, pid);
 		if (access(path, R_OK)) {
 			pr_err("Can't access file %s\n", path);
+			machine = NULL;
 			goto out;
 		}
 		root_dir = path;
 	}
+
 	machine = machines__add(self, pid, root_dir);
-	}
 
 out:
 	return machine;