[RFC patch 26/41] mm/page_owner: Simplify stack trace handling

[Thomas Gleixner]

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

The original code in all printing functions is really wrong. It allocates a
storage array on stack which is unused because depot_fetch_stack() does not
store anything in it. It overwrites the entries pointer in the stack_trace
struct so it points to the depot storage.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
 mm/page_owner.c |   79 +++++++++++++++++++-------------------------------------
 1 file changed, 28 insertions(+), 51 deletions(-)

--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -58,15 +58,10 @@ static bool need_page_owner(void)
 static __always_inline depot_stack_handle_t create_dummy_stack(void)
 {
 	unsigned long entries[4];
-	struct stack_trace dummy;
+	unsigned int nent;
 
-	dummy.nr_entries = 0;
-	dummy.max_entries = ARRAY_SIZE(entries);
-	dummy.entries = &entries[0];
-	dummy.skip = 0;
-
-	save_stack_trace(&dummy);
-	return depot_save_stack(&dummy, GFP_KERNEL);
+	nent = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
+	return stack_depot_save(entries, nent, GFP_KERNEL);
 }
 
 static noinline void register_dummy_stack(void)
@@ -120,46 +115,39 @@ void __reset_page_owner(struct page *pag
 	}
 }
 
-static inline bool check_recursive_alloc(struct stack_trace *trace,
-					unsigned long ip)
+static inline bool check_recursive_alloc(unsigned long *entries,
+					 unsigned int nr_entries,
+					 unsigned long ip)
 {
-	int i;
+	unsigned int i;
 
-	if (!trace->nr_entries)
-		return false;
-
-	for (i = 0; i < trace->nr_entries; i++) {
-		if (trace->entries[i] == ip)
+	for (i = 0; i < nr_entries; i++) {
+		if (entries[i] == ip)
 			return true;
 	}
-
 	return false;
 }
 
 static noinline depot_stack_handle_t save_stack(gfp_t flags)
 {
 	unsigned long entries[PAGE_OWNER_STACK_DEPTH];
-	struct stack_trace trace = {
-		.nr_entries = 0,
-		.entries = entries,
-		.max_entries = PAGE_OWNER_STACK_DEPTH,
-		.skip = 2
-	};
 	depot_stack_handle_t handle;
+	unsigned int nent;
 
-	save_stack_trace(&trace);
+	nent = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
 
 	/*
-	 * We need to check recursion here because our request to stackdepot
-	 * could trigger memory allocation to save new entry. New memory
-	 * allocation would reach here and call depot_save_stack() again
-	 * if we don't catch it. There is still not enough memory in stackdepot
-	 * so it would try to allocate memory again and loop forever.
+	 * We need to check recursion here because our request to
+	 * stackdepot could trigger memory allocation to save new
+	 * entry. New memory allocation would reach here and call
+	 * stack_depot_save_entries() again if we don't catch it. There is
+	 * still not enough memory in stackdepot so it would try to
+	 * allocate memory again and loop forever.
 	 */
-	if (check_recursive_alloc(&trace, _RET_IP_))
+	if (check_recursive_alloc(entries, nent, _RET_IP_))
 		return dummy_handle;
 
-	handle = depot_save_stack(&trace, flags);
+	handle = stack_depot_save(entries, nent, flags);
 	if (!handle)
 		handle = failure_handle;
 
@@ -337,16 +325,10 @@ print_page_owner(char __user *buf, size_
 		struct page *page, struct page_owner *page_owner,
 		depot_stack_handle_t handle)
 {
-	int ret;
-	int pageblock_mt, page_mt;
+	int ret, pageblock_mt, page_mt;
+	unsigned long *entries;
+	unsigned int nent;
 	char *kbuf;
-	unsigned long entries[PAGE_OWNER_STACK_DEPTH];
-	struct stack_trace trace = {
-		.nr_entries = 0,
-		.entries = entries,
-		.max_entries = PAGE_OWNER_STACK_DEPTH,
-		.skip = 0
-	};
 
 	count = min_t(size_t, count, PAGE_SIZE);
 	kbuf = kmalloc(count, GFP_KERNEL);
@@ -375,8 +357,8 @@ print_page_owner(char __user *buf, size_
 	if (ret >= count)
 		goto err;
 
-	depot_fetch_stack(handle, &trace);
-	ret += snprint_stack_trace(kbuf + ret, count - ret, &trace, 0);
+	nent = stack_depot_fetch(handle, &entries);
+	ret += stack_trace_snprint(kbuf + ret, count - ret, entries, nent, 0);
 	if (ret >= count)
 		goto err;
 
@@ -407,14 +389,9 @@ void __dump_page_owner(struct page *page
 {
 	struct page_ext *page_ext = lookup_page_ext(page);
 	struct page_owner *page_owner;
-	unsigned long entries[PAGE_OWNER_STACK_DEPTH];
-	struct stack_trace trace = {
-		.nr_entries = 0,
-		.entries = entries,
-		.max_entries = PAGE_OWNER_STACK_DEPTH,
-		.skip = 0
-	};
 	depot_stack_handle_t handle;
+	unsigned long *entries;
+	unsigned int nent;
 	gfp_t gfp_mask;
 	int mt;
 
@@ -438,10 +415,10 @@ void __dump_page_owner(struct page *page
 		return;
 	}
 
-	depot_fetch_stack(handle, &trace);
+	nent = stack_depot_fetch(handle, &entries);
 	pr_alert("page allocated via order %u, migratetype %s, gfp_mask %#x(%pGg)\n",
 		 page_owner->order, migratetype_names[mt], gfp_mask, &gfp_mask);
-	print_stack_trace(&trace, 0);
+	stack_trace_print(entries, nent, 0);
 
 	if (page_owner->last_migrate_reason != -1)
 		pr_alert("page has been migrated, last migrate reason: %s\n",