tracing: Simplify stack trace retrieval

Replace the indirection through struct stack_trace by using the storage
array based interfaces.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
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: Tom Zanussi <tom.zanussi@linux.intel.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: linux-arch@vger.kernel.org
Link: https://lkml.kernel.org/r/20190425094803.248604594@linutronix.de

kernel/trace/trace.c

@@ -2774,22 +2774,18 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
 {
 	struct trace_event_call *call = &event_kernel_stack;
 	struct ring_buffer_event *event;
+	unsigned int size, nr_entries;
 	struct ftrace_stack *fstack;
 	struct stack_entry *entry;
-	struct stack_trace trace;
-	int size = FTRACE_KSTACK_ENTRIES;
 	int stackidx;
 
-	trace.nr_entries	= 0;
-	trace.skip		= skip;
-
 	/*
 	 * Add one, for this function and the call to save_stack_trace()
 	 * If regs is set, then these functions will not be in the way.
 	 */
 #ifndef CONFIG_UNWINDER_ORC
 	if (!regs)
-		trace.skip++;
+		skip++;
 #endif
 
 	/*
@@ -2816,28 +2812,24 @@ static void __ftrace_trace_stack(struct ring_buffer *buffer,
 	barrier();
 
 	fstack = this_cpu_ptr(ftrace_stacks.stacks) + stackidx;
-	trace.entries		= fstack->calls;
-	trace.max_entries	= FTRACE_KSTACK_ENTRIES;
+	size = ARRAY_SIZE(fstack->calls);
 
-	if (regs)
-		save_stack_trace_regs(regs, &trace);
-	else
-		save_stack_trace(&trace);
-
-	if (trace.nr_entries > size)
-		size = trace.nr_entries;
-
-	size *= sizeof(unsigned long);
+	if (regs) {
+		nr_entries = stack_trace_save_regs(regs, fstack->calls,
+						   size, skip);
+	} else {
+		nr_entries = stack_trace_save(fstack->calls, size, skip);
+	}
 
+	size = nr_entries * sizeof(unsigned long);
 	event = __trace_buffer_lock_reserve(buffer, TRACE_STACK,
 					    sizeof(*entry) + size, flags, pc);
 	if (!event)
 		goto out;
 	entry = ring_buffer_event_data(event);
 
-	memcpy(&entry->caller, trace.entries, size);
-
-	entry->size = trace.nr_entries;
+	memcpy(&entry->caller, fstack->calls, size);
+	entry->size = nr_entries;
 
 	if (!call_filter_check_discard(call, entry, buffer, event))
 		__buffer_unlock_commit(buffer, event);
@@ -2916,7 +2908,6 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
 	struct trace_event_call *call = &event_user_stack;
 	struct ring_buffer_event *event;
 	struct userstack_entry *entry;
-	struct stack_trace trace;
 
 	if (!(global_trace.trace_flags & TRACE_ITER_USERSTACKTRACE))
 		return;
@@ -2947,12 +2938,7 @@ ftrace_trace_userstack(struct ring_buffer *buffer, unsigned long flags, int pc)
 	entry->tgid		= current->tgid;
 	memset(&entry->caller, 0, sizeof(entry->caller));
 
-	trace.nr_entries	= 0;
-	trace.max_entries	= FTRACE_STACK_ENTRIES;
-	trace.skip		= 0;
-	trace.entries		= entry->caller;
-
-	save_stack_trace_user(&trace);
+	stack_trace_save_user(entry->caller, FTRACE_STACK_ENTRIES);
 	if (!call_filter_check_discard(call, entry, buffer, event))
 		__buffer_unlock_commit(buffer, event);