proc: Simplify task stack retrieval

Replace the indirection through struct stack_trace with an invocation of
the storage array based interface.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexey Dobriyan <adobriyan@gmail.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Alexander Potapenko <glider@google.com>
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/20190425094801.589304463@linutronix.de

fs/proc/base.c

@@ -407,7 +407,6 @@ static void unlock_trace(struct task_struct *task)
 static int proc_pid_stack(struct seq_file *m, struct pid_namespace *ns,
 			  struct pid *pid, struct task_struct *task)
 {
-	struct stack_trace trace;
 	unsigned long *entries;
 	int err;
 
@@ -430,20 +429,17 @@ static int proc_pid_stack(struct seq_file *m, struct pid_namespace *ns,
 	if (!entries)
 		return -ENOMEM;
 
-	trace.nr_entries	= 0;
-	trace.max_entries	= MAX_STACK_TRACE_DEPTH;
-	trace.entries		= entries;
-	trace.skip		= 0;
-
 	err = lock_trace(task);
 	if (!err) {
-		unsigned int i;
+		unsigned int i, nr_entries;
 
-		save_stack_trace_tsk(task, &trace);
+		nr_entries = stack_trace_save_tsk(task, entries,
+						  MAX_STACK_TRACE_DEPTH, 0);
 
-		for (i = 0; i < trace.nr_entries; i++) {
+		for (i = 0; i < nr_entries; i++) {
 			seq_printf(m, "[<0>] %pB\n", (void *)entries[i]);
 		}
+
 		unlock_trace(task);
 	}
 	kfree(entries);