[PATCH v6 2/2] lib: stackdepot: Add support to disable stack depot

[vjitta@codeaurora.org]

From: Vijayanand Jitta <vjitta@codeaurora.org>

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 usecase 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.

Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org>
---
 Documentation/admin-guide/kernel-parameters.txt |  6 +++++
 include/linux/stackdepot.h                      |  1 +
 init/main.c                                     |  2 ++
 lib/stackdepot.c                                | 32 +++++++++++++++++++++----
 4 files changed, 37 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 44fde25..381fad9 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5133,6 +5133,12 @@
 			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.
 
diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
index 24d49c7..eafd9aa 100644
--- a/include/linux/stackdepot.h
+++ b/include/linux/stackdepot.h
@@ -21,4 +21,5 @@ unsigned int stack_depot_fetch(depot_stack_handle_t handle,
 
 unsigned int filter_irq_stacks(unsigned long *entries, unsigned int nr_entries);
 
+int stack_depot_init(void);
 #endif
diff --git a/init/main.c b/init/main.c
index 32b2a8a..8fcf9bb 100644
--- a/init/main.c
+++ b/init/main.c
@@ -98,6 +98,7 @@
 #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)
 	page_ext_init_flatmem();
 	init_debug_pagealloc();
 	report_meminit();
+	stack_depot_init();
 	mem_init();
 	kmem_cache_init();
 	kmemleak_init();
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index dff8521..0398658 100644
--- a/lib/stackdepot.c
+++ b/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)
 
@@ -146,9 +147,32 @@ 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] = {
-	[0 ...	STACK_HASH_SIZE - 1] = NULL
-};
+static bool stack_depot_disable;
+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)
@@ -242,7 +266,7 @@ 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);
-- 
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