perf kvm: Reference count 'struct kvm_info'

hists__add_entry_ops() doesn't allocate a new histogram entry if it has
an existing entry for a KVM event, in this case, find_create_kvm_event()
allocates a 'struct kvm_info' but it's not used by any histograms and
never freed.

To fix the memory leak, this patch first introduces a refcnt and a set
of functions for refcnt operations on 'struct kvm_info'.  When the data
structure is not anymore used (the refcnt hits zero) kvm_info__zput()
will free the memory used.

Committer:

Provide a nop version of kvm_info__zput() to be used when
HAVE_KVM_STAT_SUPPORT isn't defined as it is used unconditionally in
hists__findnew_entry() and hist_entry__delete().

Signed-off-by: Leo Yan <leo.yan@linaro.org>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230320061619.29520-2-leo.yan@linaro.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-kvm.c

@@ -768,7 +768,6 @@ static void kvm_he_free(void *he)
 {
 	struct kvm_event *kvm_ev;
 
-	free(((struct hist_entry *)he)->kvm_info);
 	kvm_ev = container_of(he, struct kvm_event, he);
 	free(kvm_ev);
 }
@@ -788,7 +787,7 @@ static struct kvm_event *find_create_kvm_event(struct perf_kvm_stat *kvm,
 
 	BUG_ON(key->key == INVALID_KEY);
 
-	ki = zalloc(sizeof(*ki));
+	ki = kvm_info__new();
 	if (!ki) {
 		pr_err("Failed to allocate kvm info\n");
 		return NULL;

tools/perf/util/hist.c

@@ -628,6 +628,8 @@ static struct hist_entry *hists__findnew_entry(struct hists *hists,
 
 			block_info__zput(entry->block_info);
 
+			kvm_info__zput(entry->kvm_info);
+
 			/* If the map of an existing hist_entry has
 			 * become out-of-date due to an exec() or
 			 * similar, update it.  Otherwise we will
@@ -1324,6 +1326,9 @@ void hist_entry__delete(struct hist_entry *he)
 	if (he->block_info)
 		block_info__zput(he->block_info);
 
+	if (he->kvm_info)
+		kvm_info__zput(he->kvm_info);
+
 	zfree(&he->res_samples);
 	zfree(&he->stat_acc);
 	free_srcline(he->srcline);

tools/perf/util/kvm-stat.h

@@ -10,6 +10,9 @@
 #include "symbol.h"
 #include "record.h"
 
+#include <stdlib.h>
+#include <linux/zalloc.h>
+
 #define KVM_EVENT_NAME_LEN	40
 
 struct evsel;
@@ -25,6 +28,7 @@ struct event_key {
 
 struct kvm_info {
 	char name[KVM_EVENT_NAME_LEN];
+	refcount_t refcnt;
 };
 
 struct kvm_event_stats {
@@ -145,6 +149,42 @@ extern const char *vcpu_id_str;
 extern const char *kvm_exit_reason;
 extern const char *kvm_entry_trace;
 extern const char *kvm_exit_trace;
+
+static inline struct kvm_info *kvm_info__get(struct kvm_info *ki)
+{
+	if (ki)
+		refcount_inc(&ki->refcnt);
+	return ki;
+}
+
+static inline void kvm_info__put(struct kvm_info *ki)
+{
+	if (ki && refcount_dec_and_test(&ki->refcnt))
+		free(ki);
+}
+
+static inline void __kvm_info__zput(struct kvm_info **ki)
+{
+	kvm_info__put(*ki);
+	*ki = NULL;
+}
+
+#define kvm_info__zput(ki) __kvm_info__zput(&ki)
+
+static inline struct kvm_info *kvm_info__new(void)
+{
+	struct kvm_info *ki;
+
+	ki = zalloc(sizeof(*ki));
+	if (ki)
+		refcount_set(&ki->refcnt, 1);
+
+	return ki;
+}
+
+#else /* HAVE_KVM_STAT_SUPPORT */
+// We use this unconditionally in hists__findnew_entry() and hist_entry__delete()
+#define kvm_info__zput(ki) do { } while (0)
 #endif /* HAVE_KVM_STAT_SUPPORT */
 
 extern int kvm_add_default_arch_event(int *argc, const char **argv);