[RFC PATCH 19/30] move stack capture functionality into a separate function for reuse

[Suren Baghdasaryan]

Make save_stack() function part of stackdepot API to be used outside of
page_owner. Also rename task_struct's in_page_owner to in_capture_stack
flag to better convey the wider use of this flag.

Signed-off-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
---
 include/linux/sched.h      |  6 ++--
 include/linux/stackdepot.h |  3 ++
 lib/stackdepot.c           | 68 ++++++++++++++++++++++++++++++++++++++
 mm/page_owner.c            | 52 ++---------------------------
 4 files changed, 77 insertions(+), 52 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index e7b2f8a5c711..d06cad6c14bd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -930,9 +930,9 @@ struct task_struct {
 	/* Stalled due to lack of memory */
 	unsigned			in_memstall:1;
 #endif
-#ifdef CONFIG_PAGE_OWNER
-	/* Used by page_owner=on to detect recursion in page tracking. */
-	unsigned			in_page_owner:1;
+#ifdef CONFIG_STACKDEPOT
+	/* Used by stack_depot_capture_stack to detect recursion. */
+	unsigned			in_capture_stack:1;
 #endif
 #ifdef CONFIG_EVENTFD
 	/* Recursion prevention for eventfd_signal() */
diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index bc2797955de9..8dc9fdb2c4dd 100644
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -64,4 +64,7 @@ int stack_depot_snprint(depot_stack_handle_t handle, char *buf, size_t size,
 
 void stack_depot_print(depot_stack_handle_t stack);
 
+bool stack_depot_capture_init(void);
+depot_stack_handle_t stack_depot_capture_stack(gfp_t flags);
+
 #endif
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index e73fda23388d..c8615bd6dc25 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -514,3 +514,71 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
 	return __stack_depot_save(entries, nr_entries, alloc_flags, true);
 }
 EXPORT_SYMBOL_GPL(stack_depot_save);
+
+static depot_stack_handle_t recursion_handle;
+static depot_stack_handle_t failure_handle;
+
+static __always_inline depot_stack_handle_t create_custom_stack(void)
+{
+	unsigned long entries[4];
+	unsigned int nr_entries;
+
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
+	return stack_depot_save(entries, nr_entries, GFP_KERNEL);
+}
+
+static noinline void register_recursion_stack(void)
+{
+	recursion_handle = create_custom_stack();
+}
+
+static noinline void register_failure_stack(void)
+{
+	failure_handle = create_custom_stack();
+}
+
+bool stack_depot_capture_init(void)
+{
+	static DEFINE_MUTEX(stack_depot_capture_init_mutex);
+	static bool utility_stacks_ready;
+
+	mutex_lock(&stack_depot_capture_init_mutex);
+	if (!utility_stacks_ready) {
+		register_recursion_stack();
+		register_failure_stack();
+		utility_stacks_ready = true;
+	}
+	mutex_unlock(&stack_depot_capture_init_mutex);
+
+	return utility_stacks_ready;
+}
+
+/* TODO: teach stack_depot_capture_stack to use off stack temporal storage */
+#define CAPTURE_STACK_DEPTH (16)
+
+depot_stack_handle_t stack_depot_capture_stack(gfp_t flags)
+{
+	unsigned long entries[CAPTURE_STACK_DEPTH];
+	depot_stack_handle_t handle;
+	unsigned int nr_entries;
+
+	/*
+	 * Avoid recursion.
+	 *
+	 * Sometimes page metadata allocation tracking requires more
+	 * memory to be allocated:
+	 * - when new stack trace is saved to stack depot
+	 * - when backtrace itself is calculated (ia64)
+	 */
+	if (current->in_capture_stack)
+		return recursion_handle;
+	current->in_capture_stack = 1;
+
+	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
+	handle = stack_depot_save(entries, nr_entries, flags);
+	if (!handle)
+		handle = failure_handle;
+
+	current->in_capture_stack = 0;
+	return handle;
+}
diff --git a/mm/page_owner.c b/mm/page_owner.c
index fd4af1ad34b8..c3173e34a779 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -15,12 +15,6 @@
 
 #include "internal.h"
 
-/*
- * TODO: teach PAGE_OWNER_STACK_DEPTH (__dump_page_owner and save_stack)
- * to use off stack temporal storage
- */
-#define PAGE_OWNER_STACK_DEPTH (16)
-
 struct page_owner {
 	unsigned short order;
 	short last_migrate_reason;
@@ -37,8 +31,6 @@ struct page_owner {
 static bool page_owner_enabled __initdata;
 DEFINE_STATIC_KEY_FALSE(page_owner_inited);
 
-static depot_stack_handle_t dummy_handle;
-static depot_stack_handle_t failure_handle;
 static depot_stack_handle_t early_handle;
 
 static void init_early_allocated_pages(void);
@@ -68,16 +60,6 @@ static __always_inline depot_stack_handle_t create_dummy_stack(void)
 	return stack_depot_save(entries, nr_entries, GFP_KERNEL);
 }
 
-static noinline void register_dummy_stack(void)
-{
-	dummy_handle = create_dummy_stack();
-}
-
-static noinline void register_failure_stack(void)
-{
-	failure_handle = create_dummy_stack();
-}
-
 static noinline void register_early_stack(void)
 {
 	early_handle = create_dummy_stack();
@@ -88,8 +70,7 @@ static __init void init_page_owner(void)
 	if (!page_owner_enabled)
 		return;
 
-	register_dummy_stack();
-	register_failure_stack();
+	stack_depot_capture_init();
 	register_early_stack();
 	static_branch_enable(&page_owner_inited);
 	init_early_allocated_pages();
@@ -106,33 +87,6 @@ static inline struct page_owner *get_page_owner(struct page_ext *page_ext)
 	return (void *)page_ext + page_owner_ops.offset;
 }
 
-static noinline depot_stack_handle_t save_stack(gfp_t flags)
-{
-	unsigned long entries[PAGE_OWNER_STACK_DEPTH];
-	depot_stack_handle_t handle;
-	unsigned int nr_entries;
-
-	/*
-	 * Avoid recursion.
-	 *
-	 * Sometimes page metadata allocation tracking requires more
-	 * memory to be allocated:
-	 * - when new stack trace is saved to stack depot
-	 * - when backtrace itself is calculated (ia64)
-	 */
-	if (current->in_page_owner)
-		return dummy_handle;
-	current->in_page_owner = 1;
-
-	nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 2);
-	handle = stack_depot_save(entries, nr_entries, flags);
-	if (!handle)
-		handle = failure_handle;
-
-	current->in_page_owner = 0;
-	return handle;
-}
-
 void __reset_page_owner(struct page *page, unsigned short order)
 {
 	int i;
@@ -145,7 +99,7 @@ void __reset_page_owner(struct page *page, unsigned short order)
 	if (unlikely(!page_ext))
 		return;
 
-	handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
+	handle = stack_depot_capture_stack(GFP_NOWAIT | __GFP_NOWARN);
 	for (i = 0; i < (1 << order); i++) {
 		__clear_bit(PAGE_EXT_OWNER_ALLOCATED, &page_ext->flags);
 		page_owner = get_page_owner(page_ext);
@@ -189,7 +143,7 @@ noinline void __set_page_owner(struct page *page, unsigned short order,
 	if (unlikely(!page_ext))
 		return;
 
-	handle = save_stack(gfp_mask);
+	handle = stack_depot_capture_stack(gfp_mask);
 	__set_page_owner_handle(page_ext, handle, order, gfp_mask);
 }
 
-- 
2.37.2.672.g94769d06f0-goog