lib, stackdepot: add helper to print stack entries into buffer

To print stack entries into a buffer, users of stackdepot, first get a
list of stack entries using stack_depot_fetch and then print this list
into a buffer using stack_trace_snprint.  Provide a helper in stackdepot
for this purpose.  Also change above mentioned users to use this helper.

[imran.f.khan@oracle.com: fix build error]
  Link: https://lkml.kernel.org/r/20210915175321.3472770-4-imran.f.khan@oracle.com
[imran.f.khan@oracle.com: export stack_depot_snprint() to modules]
  Link: https://lkml.kernel.org/r/20210916133535.3592491-4-imran.f.khan@oracle.com

Link: https://lkml.kernel.org/r/20210915014806.3206938-4-imran.f.khan@oracle.com
Signed-off-by: Imran Khan <imran.f.khan@oracle.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Jani Nikula <jani.nikula@intel.com>	[i915]
Cc: Alexander Potapenko <glider@google.com>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -1668,13 +1668,10 @@ __dump_topology_ref_history(struct drm_dp_mst_topology_ref_history *history,
 	for (i = 0; i < history->len; i++) {
 		const struct drm_dp_mst_topology_ref_entry *entry =
 			&history->entries[i];
-		ulong *entries;
-		uint nr_entries;
 		u64 ts_nsec = entry->ts_nsec;
 		u32 rem_nsec = do_div(ts_nsec, 1000000000);
 
-		nr_entries = stack_depot_fetch(entry->backtrace, &entries);
-		stack_trace_snprint(buf, PAGE_SIZE, entries, nr_entries, 4);
+		stack_depot_snprint(entry->backtrace, buf, PAGE_SIZE, 4);
 
 		drm_printf(&p, "  %d %ss (last at %5llu.%06u):\n%s",
 			   entry->count,

drivers/gpu/drm/drm_mm.c

@@ -118,8 +118,6 @@ static noinline void save_stack(struct drm_mm_node *node)
 static void show_leaks(struct drm_mm *mm)
 {
 	struct drm_mm_node *node;
-	unsigned long *entries;
-	unsigned int nr_entries;
 	char *buf;
 
 	buf = kmalloc(BUFSZ, GFP_KERNEL);
@@ -133,8 +131,7 @@ static void show_leaks(struct drm_mm *mm)
 			continue;
 		}
 
-		nr_entries = stack_depot_fetch(node->stack, &entries);
-		stack_trace_snprint(buf, BUFSZ, entries, nr_entries, 0);
+		stack_depot_snprint(node->stack, buf, BUFSZ, 0);
 		DRM_ERROR("node [%08llx + %08llx]: inserted at\n%s",
 			  node->start, node->size, buf);
 	}

drivers/gpu/drm/i915/i915_vma.c

@@ -56,8 +56,6 @@ void i915_vma_free(struct i915_vma *vma)
 
 static void vma_print_allocator(struct i915_vma *vma, const char *reason)
 {
-	unsigned long *entries;
-	unsigned int nr_entries;
 	char buf[512];
 
 	if (!vma->node.stack) {
@@ -66,8 +64,7 @@ static void vma_print_allocator(struct i915_vma *vma, const char *reason)
 		return;
 	}
 
-	nr_entries = stack_depot_fetch(vma->node.stack, &entries);
-	stack_trace_snprint(buf, sizeof(buf), entries, nr_entries, 0);
+	stack_depot_snprint(vma->node.stack, buf, sizeof(buf), 0);
 	DRM_DEBUG_DRIVER("vma.node [%08llx + %08llx] %s: inserted at %s\n",
 			 vma->node.start, vma->node.size, reason, buf);
 }

drivers/gpu/drm/i915/intel_runtime_pm.c

@@ -65,16 +65,6 @@ static noinline depot_stack_handle_t __save_depot_stack(void)
 	return stack_depot_save(entries, n, GFP_NOWAIT | __GFP_NOWARN);
 }
 
-static void __print_depot_stack(depot_stack_handle_t stack,
-				char *buf, int sz, int indent)
-{
-	unsigned long *entries;
-	unsigned int nr_entries;
-
-	nr_entries = stack_depot_fetch(stack, &entries);
-	stack_trace_snprint(buf, sz, entries, nr_entries, indent);
-}
-
 static void init_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm)
 {
 	spin_lock_init(&rpm->debug.lock);
@@ -146,12 +136,12 @@ static void untrack_intel_runtime_pm_wakeref(struct intel_runtime_pm *rpm,
 		if (!buf)
 			return;
 
-		__print_depot_stack(stack, buf, PAGE_SIZE, 2);
+		stack_depot_snprint(stack, buf, PAGE_SIZE, 2);
 		DRM_DEBUG_DRIVER("wakeref %x from\n%s", stack, buf);
 
 		stack = READ_ONCE(rpm->debug.last_release);
 		if (stack) {
-			__print_depot_stack(stack, buf, PAGE_SIZE, 2);
+			stack_depot_snprint(stack, buf, PAGE_SIZE, 2);
 			DRM_DEBUG_DRIVER("wakeref last released at\n%s", buf);
 		}
 
@@ -183,12 +173,12 @@ __print_intel_runtime_pm_wakeref(struct drm_printer *p,
 		return;
 
 	if (dbg->last_acquire) {
-		__print_depot_stack(dbg->last_acquire, buf, PAGE_SIZE, 2);
+		stack_depot_snprint(dbg->last_acquire, buf, PAGE_SIZE, 2);
 		drm_printf(p, "Wakeref last acquired:\n%s", buf);
 	}
 
 	if (dbg->last_release) {
-		__print_depot_stack(dbg->last_release, buf, PAGE_SIZE, 2);
+		stack_depot_snprint(dbg->last_release, buf, PAGE_SIZE, 2);
 		drm_printf(p, "Wakeref last released:\n%s", buf);
 	}
 
@@ -203,7 +193,7 @@ __print_intel_runtime_pm_wakeref(struct drm_printer *p,
 		rep = 1;
 		while (i + 1 < dbg->count && dbg->owners[i + 1] == stack)
 			rep++, i++;
-		__print_depot_stack(stack, buf, PAGE_SIZE, 2);
+		stack_depot_snprint(stack, buf, PAGE_SIZE, 2);
 		drm_printf(p, "Wakeref x%lu taken at:\n%s", rep, buf);
 	}
 

include/linux/stackdepot.h

@@ -25,6 +25,9 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
 unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 			       unsigned long **entries);
 
+int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
+		       int spaces);
+
 void stack_depot_print(depot_stack_handle_t stack);
 
 #ifdef CONFIG_STACKDEPOT

lib/stackdepot.c

@@ -213,6 +213,31 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
 	return NULL;
 }
 
+/**
+ * stack_depot_snprint - print stack entries from a depot into a buffer
+ *
+ * @handle:	Stack depot handle which was returned from
+ *		stack_depot_save().
+ * @buf:	Pointer to the print buffer
+ *
+ * @size:	Size of the print buffer
+ *
+ * @spaces:	Number of leading spaces to print
+ *
+ * Return:	Number of bytes printed.
+ */
+int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
+		       int spaces)
+{
+	unsigned long *entries;
+	unsigned int nr_entries;
+
+	nr_entries = stack_depot_fetch(handle, &entries);
+	return nr_entries ? stack_trace_snprint(buf, size, entries, nr_entries,
+						spaces) : 0;
+}
+EXPORT_SYMBOL_GPL(stack_depot_snprint);
+
 /**
  * stack_depot_print - print stack entries from a depot
  *

mm/page_owner.c

@@ -329,8 +329,6 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 		depot_stack_handle_t handle)
 {
 	int ret, pageblock_mt, page_mt;
-	unsigned long *entries;
-	unsigned int nr_entries;
 	char *kbuf;
 
 	count = min_t(size_t, count, PAGE_SIZE);
@@ -361,8 +359,7 @@ print_page_owner(char __user *buf, size_t count, unsigned long pfn,
 	if (ret >= count)
 		goto err;
 
-	nr_entries = stack_depot_fetch(handle, &entries);
-	ret += stack_trace_snprint(kbuf + ret, count - ret, entries, nr_entries, 0);
+	ret += stack_depot_snprint(handle, kbuf + ret, count - ret, 0);
 	if (ret >= count)
 		goto err;