[PATCH] lib/stackdepot: Use page allocator if both slab and memblock is unavailable

[Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>]

After commit 2dba5eb1c73b ("lib/stackdepot: allow optional init and
stack_table allocation by kvmalloc()"), stack_depot_init() is called
later if CONFIG_STACKDEPOT_ALWAYS_INIT=n to remove unnecessary memory
usage. It allocates stack_table using memblock_alloc() or kvmalloc()
depending on availability of slab allocator.

But when stack_depot_init() is called while creating boot slab caches,
both slab allocator and memblock is not available. So kernel crashes.
Allocate stack_table from page allocator when both slab allocator and
memblock is unavailable.

Limit size of stack_table when using page allocator because vmalloc()
is also unavailable in kmem_cache_init(). it must not be larger than
(PAGE_SIZE << (MAX_ORDER - 1)).

This patch was tested on both CONFIG_STACKDEPOT_ALWAYS_INIT=y and n.

Fixes: 2dba5eb1c73b ("lib/stackdepot: allow optional init and stack_table allocation by kvmalloc()")
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
---
 lib/stackdepot.c | 28 +++++++++++++++++++++-------
 1 file changed, 21 insertions(+), 7 deletions(-)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index bf5ba9af0500..606f80ae2bf7 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -73,6 +73,14 @@ static int next_slab_inited;
 static size_t depot_offset;
 static DEFINE_RAW_SPINLOCK(depot_lock);
 
+static unsigned int stack_hash_size = (1 << CONFIG_STACK_HASH_ORDER);
+static inline unsigned int stack_hash_mask(void)
+{
+	return stack_hash_size - 1;
+}
+
+#define STACK_HASH_SEED 0x9747b28c
+
 static bool init_stack_slab(void **prealloc)
 {
 	if (!*prealloc)
@@ -142,10 +150,6 @@ depot_alloc_stack(unsigned long *entries, int size, u32 hash, void **prealloc)
 	return stack;
 }
 
-#define STACK_HASH_SIZE (1L << CONFIG_STACK_HASH_ORDER)
-#define STACK_HASH_MASK (STACK_HASH_SIZE - 1)
-#define STACK_HASH_SEED 0x9747b28c
-
 static bool stack_depot_disable;
 static struct stack_record **stack_table;
 
@@ -172,18 +176,28 @@ __ref int stack_depot_init(void)
 
 	mutex_lock(&stack_depot_init_mutex);
 	if (!stack_depot_disable && !stack_table) {
-		size_t size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
+		size_t size = (stack_hash_size * sizeof(struct stack_record *));
 		int i;
 
 		if (slab_is_available()) {
 			pr_info("Stack Depot allocating hash table with kvmalloc\n");
 			stack_table = kvmalloc(size, GFP_KERNEL);
+		} else if (totalram_pages() > 0) {
+			/* Reduce size because vmalloc may be unavailable */
+			size = min(size, PAGE_SIZE << (MAX_ORDER - 1));
+			stack_hash_size = size / sizeof(struct stack_record *);
+
+			pr_info("Stack Depot allocating hash table with __get_free_pages\n");
+			stack_table = (struct stack_record **)
+				      __get_free_pages(GFP_KERNEL, get_order(size));
 		} else {
 			pr_info("Stack Depot allocating hash table with memblock_alloc\n");
 			stack_table = memblock_alloc(size, SMP_CACHE_BYTES);
 		}
+
 		if (stack_table) {
-			for (i = 0; i < STACK_HASH_SIZE;  i++)
+			pr_info("Stack Depot hash table size=%u\n", stack_hash_size);
+			for (i = 0; i < stack_hash_size;  i++)
 				stack_table[i] = NULL;
 		} else {
 			pr_err("Stack Depot hash table allocation failed, disabling\n");
@@ -363,7 +377,7 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
 		goto fast_exit;
 
 	hash = hash_stack(entries, nr_entries);
-	bucket = &stack_table[hash & STACK_HASH_MASK];
+	bucket = &stack_table[hash & stack_hash_mask()];
 
 	/*
 	 * Fast path: look the stack trace up without locking.
-- 
2.33.1