perf evlist: Fix errno value reporting on failed mmap

On failure, perf_evlist__mmap_per_{cpu,thread} will try to munmap()
every map that doesn't have a NULL base. This will fail with EINVAL if
one of them has base == MAP_FAILED, clobbering errno, so that
perf_evlist__map will return EINVAL on any failure regardless of the
root cause.

Fix this by resetting failed maps to a NULL base.

Acked-by: Namhyung Kim <namhyung@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1324301972-22740-2-git-send-email-nelhage@nelhage.com
Signed-off-by: Nelson Elhage <nelhage@nelhage.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/evlist.c

@@ -447,8 +447,10 @@ static int __perf_evlist__mmap(struct perf_evlist *evlist,
 	evlist->mmap[idx].mask = mask;
 	evlist->mmap[idx].base = mmap(NULL, evlist->mmap_len, prot,
 				      MAP_SHARED, fd, 0);
-	if (evlist->mmap[idx].base == MAP_FAILED)
+	if (evlist->mmap[idx].base == MAP_FAILED) {
+		evlist->mmap[idx].base = NULL;
 		return -1;
+	}
 
 	perf_evlist__add_pollfd(evlist, fd);
 	return 0;