lib: stackdepot: add support to disable stack depot

Add a kernel parameter stack_depot_disable to disable stack depot.  So
that stack hash table doesn't consume any memory when stack depot is
disabled.

The use case is CONFIG_PAGE_OWNER without page_owner=on.  Without this
patch, stackdepot will consume the memory for the hashtable.  By default,
it's 8M which is never trivial.

With this option, in CONFIG_PAGE_OWNER configured system, page_owner=off,
stack_depot_disable in kernel command line, we could save the wasted
memory for the hashtable.

[akpm@linux-foundation.org: fix CONFIG_STACKDEPOT=n build]

Link: https://lkml.kernel.org/r/1611749198-24316-2-git-send-email-vjitta@codeaurora.org
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org>
Cc: Alexander Potapenko <glider@google.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Yogesh Lal <ylal@codeaurora.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/admin-guide/kernel-parameters.txt

@@ -5182,6 +5182,12 @@
 			growing up) the main stack are reserved for no other
 			mapping. Default value is 256 pages.
 
+	stack_depot_disable= [KNL]
+			Setting this to true through kernel command line will
+			disable the stack depot thereby saving the static memory
+			consumed by the stack hash table. By default this is set
+			to false.
+
 	stacktrace	[FTRACE]
 			Enabled the stack tracer on boot up.
 

include/linux/stackdepot.h

@@ -21,4 +21,13 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 
 unsigned int filter_irq_stacks(unsigned long *entries, unsigned int nr_entries);
 
+#ifdef CONFIG_STACKDEPOT
+int stack_depot_init(void);
+#else
+static inline int stack_depot_init(void)
+{
+	return 0;
+}
+#endif	/* CONFIG_STACKDEPOT */
+
 #endif

init/main.c

@@ -97,6 +97,7 @@
 #include <linux/mem_encrypt.h>
 #include <linux/kcsan.h>
 #include <linux/init_syscalls.h>
+#include <linux/stackdepot.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -827,6 +828,7 @@ static void __init mm_init(void)
 	init_mem_debugging_and_hardening();
 	kfence_alloc_pool();
 	report_meminit();
+	stack_depot_init();
 	mem_init();
 	/* page_owner must be initialized after buddy is ready */
 	page_ext_init_flatmem_late();

lib/stackdepot.c

@@ -31,6 +31,7 @@
 #include <linux/stackdepot.h>
 #include <linux/string.h>
 #include <linux/types.h>
+#include <linux/memblock.h>
 
 #define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)
 
@@ -145,9 +146,32 @@ static struct stack_record *depot_alloc_stack(unsigned long *entries, int size,
 #define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
 #define STACK_HASH_SEED 0x9747b28c
 
-static struct stack_record *stack_table[STACK_HASH_SIZE] = {
+static bool stack_depot_disable;
-	[0 ...	STACK_HASH_SIZE - 1] = NULL
+static struct stack_record **stack_table;
-};
+
+static int __init is_stack_depot_disabled(char *str)
+{
+	kstrtobool(str, &stack_depot_disable);
+	if (stack_depot_disable) {
+		pr_info("Stack Depot is disabled\n");
+		stack_table = NULL;
+	}
+	return 0;
+}
+early_param("stack_depot_disable", is_stack_depot_disabled);
+
+int __init stack_depot_init(void)
+{
+	if (!stack_depot_disable) {
+		size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
+		int i;
+
+		stack_table = memblock_alloc(size, size);
+		for (i = 0; i < STACK_HASH_SIZE;  i++)
+			stack_table[i] = NULL;
+	}
+	return 0;
+}
 
 /* Calculate hash for a stack */
 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
@@ -241,7 +265,7 @@ depot_stack_handle_t stack_depot_save(unsigned long *entries,
 	unsigned long flags;
 	u32 hash;
 
-	if (unlikely(nr_entries == 0))
+	if (unlikely(nr_entries == 0) || stack_depot_disable)
 		goto fast_exit;
 
 	hash = hash_stack(entries, nr_entries);