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

[Marco Elver <elver@google.com>]

On Sun, 27 Feb 2022 at 04:08, Hyeonggon Yoo <42.hyeyoo@gmail.com> wrote:
>
> 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.

This is odd - who is calling stack_depot_init() while neither slab nor
memblock are available? Do you have a stacktrace?

> 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@gmail.com>
> ---
>  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