[PATCH v4 2/2] lib: stackdepot: Add support to disable stack depot

[vjitta]

From: Vijayanand Jitta <vji...@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.

Signed-off-by: Vinayak Menon <vinme...@codeaurora.org>
Signed-off-by: Vijayanand Jitta <vji...@codeaurora.org>
---
 lib/stackdepot.c | 31 +++++++++++++++++++++++++++++--
 1 file changed, 29 insertions(+), 2 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 614ac28..72b9050 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -30,6 +30,7 @@
 #include <linux/stackdepot.h>
 #include <linux/string.h>
 #include <linux/types.h>
+#include <linux/vmalloc.h>
 
 #define DEPOT_STACK_BITS (sizeof(depot_stack_handle_t) * 8)
 
@@ -145,10 +146,36 @@ 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 struct stack_record *stack_table_tmp[STACK_HASH_SIZE] __initdata = {
        [0 ...  STACK_HASH_SIZE - 1] = NULL
 };
 
+static bool stack_depot_disable;
+static struct stack_record **stack_table __refdata = stack_table_tmp;
+
+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);
+
+static int __init init_stackdepot(void)
+{
+       if (!stack_depot_disable) {
+               size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
+
+               stack_table = vmalloc(size);
+               memcpy(stack_table, stack_table_tmp, size);
+       }
+       return 0;
+}
+early_initcall(init_stackdepot);
+
 /* Calculate hash for a stack */
 static inline u32 hash_stack(unsigned long *entries, unsigned int size)
 {
@@ -230,7 +257,7 @@ 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_table)
                goto fast_exit;
 
        hash = hash_stack(entries, nr_entries);
-- 
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2.7.4