tracing: Simplify stacktrace retrieval in histograms

The indirection through struct stack_trace is not necessary at all. Use the
storage array based interface.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Reviewed-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: linux-mm@kvack.org
Cc: David Rientjes <rientjes@google.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: kasan-dev@googlegroups.com
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: iommu@lists.linux-foundation.org
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: David Sterba <dsterba@suse.com>
Cc: Chris Mason <clm@fb.com>
Cc: Josef Bacik <josef@toxicpanda.com>
Cc: linux-btrfs@vger.kernel.org
Cc: dm-devel@redhat.com
Cc: Mike Snitzer <snitzer@redhat.com>
Cc: Alasdair Kergon <agk@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: dri-devel@lists.freedesktop.org
Cc: David Airlie <airlied@linux.ie>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: linux-arch@vger.kernel.org
Link: https://lkml.kernel.org/r/20190425094802.979089273@linutronix.de

kernel/trace/trace_events_hist.c

@@ -5186,7 +5186,6 @@ static void event_hist_trigger(struct event_trigger_data *data, void *rec,
 	u64 var_ref_vals[TRACING_MAP_VARS_MAX];
 	char compound_key[HIST_KEY_SIZE_MAX];
 	struct tracing_map_elt *elt = NULL;
-	struct stack_trace stacktrace;
 	struct hist_field *key_field;
 	u64 field_contents;
 	void *key = NULL;
@@ -5198,14 +5197,9 @@ static void event_hist_trigger(struct event_trigger_data *data, void *rec,
 		key_field = hist_data->fields[i];
 
 		if (key_field->flags & HIST_FIELD_FL_STACKTRACE) {
-			stacktrace.max_entries = HIST_STACKTRACE_DEPTH;
-			stacktrace.entries = entries;
-			stacktrace.nr_entries = 0;
-			stacktrace.skip = HIST_STACKTRACE_SKIP;
-
-			memset(stacktrace.entries, 0, HIST_STACKTRACE_SIZE);
-			save_stack_trace(&stacktrace);
-
+			memset(entries, 0, HIST_STACKTRACE_SIZE);
+			stack_trace_save(entries, HIST_STACKTRACE_DEPTH,
+					 HIST_STACKTRACE_SKIP);
 			key = entries;
 		} else {
 			field_contents = key_field->fn(key_field, elt, rbe, rec);