[tip:perf/urgent] perf machine: Do not bail out if not managing to read ref reloc symbol

[tip-bot for Arnaldo Carvalho de Melo]

Commit-ID:  45e90056904b12d8dd74e0d2ea6dfd5e4394104d
Gitweb:     http://git.kernel.org/tip/45e90056904b12d8dd74e0d2ea6dfd5e4394104d
Author:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
AuthorDate: Tue, 17 May 2016 11:52:26 -0300
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Fri, 20 May 2016 11:43:54 -0300

perf machine: Do not bail out if not managing to read ref reloc symbol

This means the user can't access /proc/kallsyms, for instance, because
/proc/sys/kernel/kptr_restrict is set to 1.

Instead leave the ref_reloc_sym as NULL and code using it will cope.

This allows 'perf trace' to work on such systems for !root, the only
issue would be when trying to resolve kernel symbols, which happens,
for instance, in some libtracevent plugins.  A warning for that case
will be provided in the next patch in this series.

Noticed in Ubuntu 16.04, that comes with kptr_restrict=1.

Reported-by: Milian Wolff <milian.wolff@xxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
Link: http://lkml.kernel.org/n/tip-knpu3z4iyp2dxpdfm798fac4@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/perf/util/machine.c | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 7ba9fad..b277984 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -1135,10 +1135,10 @@ int machine__create_kernel_maps(struct machine *machine)
 {
 	struct dso *kernel = machine__get_kernel(machine);
 	const char *name;
-	u64 addr = machine__get_running_kernel_start(machine, &name);
+	u64 addr;
 	int ret;
 
-	if (!addr || kernel == NULL)
+	if (kernel == NULL)
 		return -1;
 
 	ret = __machine__create_kernel_maps(machine, kernel);
@@ -1160,8 +1160,9 @@ int machine__create_kernel_maps(struct machine *machine)
 	 */
 	map_groups__fixup_end(&machine->kmaps);
 
-	if (maps__set_kallsyms_ref_reloc_sym(machine->vmlinux_maps, name,
-					     addr)) {
+	addr = machine__get_running_kernel_start(machine, &name);
+	if (!addr) {
+	} else if (maps__set_kallsyms_ref_reloc_sym(machine->vmlinux_maps, name, addr)) {
 		machine__destroy_kernel_maps(machine);
 		return -1;
 	}