livepatch: 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: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.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: linux-arch@vger.kernel.org
Link: https://lkml.kernel.org/r/20190425094803.437950229@linutronix.de

kernel/livepatch/transition.c

@@ -202,15 +202,15 @@ void klp_update_patch_state(struct task_struct *task)
  * Determine whether the given stack trace includes any references to a
  * to-be-patched or to-be-unpatched function.
  */
-static int klp_check_stack_func(struct klp_func *func,
-				struct stack_trace *trace)
+static int klp_check_stack_func(struct klp_func *func, unsigned long *entries,
+				unsigned int nr_entries)
 {
 	unsigned long func_addr, func_size, address;
 	struct klp_ops *ops;
 	int i;
 
-	for (i = 0; i < trace->nr_entries; i++) {
-		address = trace->entries[i];
+	for (i = 0; i < nr_entries; i++) {
+		address = entries[i];
 
 		if (klp_target_state == KLP_UNPATCHED) {
 			 /*
@@ -254,29 +254,25 @@ static int klp_check_stack_func(struct klp_func *func,
 static int klp_check_stack(struct task_struct *task, char *err_buf)
 {
 	static unsigned long entries[MAX_STACK_ENTRIES];
-	struct stack_trace trace;
 	struct klp_object *obj;
 	struct klp_func *func;
-	int ret;
+	int ret, nr_entries;
 
-	trace.skip = 0;
-	trace.nr_entries = 0;
-	trace.max_entries = MAX_STACK_ENTRIES;
-	trace.entries = entries;
-	ret = save_stack_trace_tsk_reliable(task, &trace);
+	ret = stack_trace_save_tsk_reliable(task, entries, ARRAY_SIZE(entries));
 	WARN_ON_ONCE(ret == -ENOSYS);
-	if (ret) {
+	if (ret < 0) {
 		snprintf(err_buf, STACK_ERR_BUF_SIZE,
 			 "%s: %s:%d has an unreliable stack\n",
 			 __func__, task->comm, task->pid);
 		return ret;
 	}
+	nr_entries = ret;
 
 	klp_for_each_object(klp_transition_patch, obj) {
 		if (!obj->patched)
 			continue;
 		klp_for_each_func(obj, func) {
-			ret = klp_check_stack_func(func, &trace);
+			ret = klp_check_stack_func(func, entries, nr_entries);
 			if (ret) {
 				snprintf(err_buf, STACK_ERR_BUF_SIZE,
 					 "%s: %s:%d is sleeping on function %s\n",