A couple hist trigger fixes

These are a couple of small fixes for problems pointed out by Dan Carpenter.

patch 1, pointed out by Smatch though not actually a bug, cleans up the code to explicitly check for something that was implied. Thanks to Steve Rostedt for suggesting the fix.

patch 2 fixes a PTR_ERR problem similar to the one previously reported by Dan.

The following changes since commit d50c744ecde7ee3ba4d7ffb0e1c55e7a2f6bbc8e:

tracing: Fix unsigned comparison to zero in hist trigger code (2016-04-19 18:56:05 -0400)

are available in the git repository at:

git://git.yoctoproject.org/linux-yocto-contrib.git tzanussi/hist-trigger-err-fixes
http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-contrib/log/?h=tzanussi/hist-trigger-err-fixes

Tom Zanussi (2):
tracing: Add check for NULL event field when creating hist field
tracing: Handle tracing_map_alloc_elts() error path correctly

 kernel/trace/trace_events_hist.c | 3 +++
 kernel/trace/tracing_map.c       | 8 ++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

1.9.3

If tracing_map_elt_alloc() fails, it will return ERR_PTR() instead of NULL, so change the check to IS_ERROR(). We also need to set the failed entry in the map->elts array to NULL instead of ERR_PTR() so tracing_map_free_elts() doesn't try freeing an ERR_PTR().

tracing_map_free_elts() should also zero out what it frees so a reentrant call won't find previously freed elements.

---
 kernel/trace/tracing_map.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

index e0f1729..979f6d6 100644
@@ -366,10 +366,13 @@ static void tracing_map_free_elts(struct tracing_map *map)
 	if (!map->elts)
 		return;
 
-	for (i = 0; i < map->max_elts; i++)
+	for (i = 0; i < map->max_elts; i++) {
 		tracing_map_elt_free(*(TRACING_MAP_ELT(map->elts, i)));
+		*(TRACING_MAP_ELT(map->elts, i)) = NULL;
+	}
 
 	tracing_map_array_free(map->elts);
+	map->elts = NULL;
 }
 
 static int tracing_map_alloc_elts(struct tracing_map *map)

@@ -383,7 +386,8 @@ static int tracing_map_alloc_elts(struct tracing_map *map)
 
 	for (i = 0; i < map->max_elts; i++) {
 		*(TRACING_MAP_ELT(map->elts, i)) = tracing_map_elt_alloc(map);
-		if (!(*(TRACING_MAP_ELT(map->elts, i)))) {
+		if (IS_ERR(*(TRACING_MAP_ELT(map->elts, i)))) {
+			*(TRACING_MAP_ELT(map->elts, i)) = NULL;
 			tracing_map_free_elts(map);
 
 			return -ENOMEM;

1.9.3

Smatch flagged create_hist_field() as possibly being able to dereference a NULL pointer, although the current code exits in all cases where the event field could be NULL, so it's not actually a problem.

Still, to prevent future changes to the code from overlooking new cases, make the NULL pointer check explicit and warn once in that case.

---
 kernel/trace/trace_events_hist.c | 3 +++
 1 file changed, 3 insertions(+)

index f98b6b3..0c05b8a 100644
@@ -371,6 +371,9 @@ static struct hist_field *create_hist_field(struct ftrace_event_field *field,
 		goto out;
 	}
 
+	if (WARN_ON_ONCE(!field))
+		goto out;
+
 	if (is_string_field(field)) {
 		flags |= HIST_FIELD_FL_STRING;
 

1.9.3

Applied.

Thanks Tom,

-- Steve