Re: [PATCH v3r0 1/6] lib/stackdepot: allow requesting early initialization dynamically

[Marco Elver]

On Thu, 3 Mar 2022 at 20:19, Vlastimil Babka <vbabka@xxxxxxx> wrote:
>
> Here's an updated version based on feedback so I don't re-send everything
> so soon after v2. Also in git:
> https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=slub-stackdepot-v3r0
> There are only trivial adaptations in patch 3/6 to the stack depot init
> changes otherwise.
> Thanks, Vlastimil
>
> ----8<----
> From 230ebae0f83540574d167f9ba1f71d3f602ca410 Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@xxxxxxx>
> Date: Wed, 2 Mar 2022 12:02:22 +0100
> Subject: [PATCH v3 1/6] lib/stackdepot: allow requesting early initialization
>  dynamically
>
> In a later patch we want to add stackdepot support for object owner
> tracking in slub caches, which is enabled by slub_debug boot parameter.
> This creates a bootstrap problem as some caches are created early in
> boot when slab_is_available() is false and thus stack_depot_init()
> tries to use memblock. But, as reported by Hyeonggon Yoo [1] we are
> already beyond memblock_free_all(). Ideally memblock allocation should
> fail, yet it succeeds, but later the system crashes, which is a
> separately handled issue.
>
> To resolve this boostrap issue in a robust way, this patch adds another
> way to request stack_depot_early_init(), which happens at a well-defined
> point of time. In addition to build-time CONFIG_STACKDEPOT_ALWAYS_INIT,
> code that's e.g. processing boot parameters (which happens early enough)
> can call a new function stack_depot_want_early_init(), which sets a flag
> that stack_depot_early_init() will check.
>
> In this patch we also convert page_owner to this approach. While it
> doesn't have the bootstrap issue as slub, it's also a functionality
> enabled by a boot param and can thus request stack_depot_early_init()
> with memblock allocation instead of later initialization with
> kvmalloc().
>
> As suggested by Mike, make stack_depot_early_init() only attempt
> memblock allocation and stack_depot_init() only attempt kvmalloc().
> Also change the latter to kvcalloc(). In both cases we can lose the
> explicit array zeroing, which the allocations do already.
>
> As suggested by Marco, provide empty implementations of the init
> functions for !CONFIG_STACKDEPOT builds to simplify the callers.
>
> [1] https://lore.kernel.org/all/YhnUcqyeMgCrWZbd@xxxxxxxxxxxxxxxxxxx-northeast-1.compute.internal/
>
> Reported-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>
> Suggested-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Suggested-by: Marco Elver <elver@xxxxxxxxxx>
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>

Looks good, thanks!

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

> ---
>  include/linux/stackdepot.h | 26 ++++++++++++---
>  lib/stackdepot.c           | 67 +++++++++++++++++++++++++-------------
>  mm/page_owner.c            |  9 +++--
>  3 files changed, 73 insertions(+), 29 deletions(-)
>
> diff --git a/include/linux/stackdepot.h b/include/linux/stackdepot.h
> index 17f992fe6355..bc2797955de9 100644
> --- a/include/linux/stackdepot.h
> +++ b/include/linux/stackdepot.h
> @@ -20,18 +20,36 @@ depot_stack_handle_t __stack_depot_save(unsigned long *entries,
>                                         gfp_t gfp_flags, bool can_alloc);
>
>  /*
> - * Every user of stack depot has to call this during its own init when it's
> - * decided that it will be calling stack_depot_save() later.
> + * Every user of stack depot has to call stack_depot_init() during its own init
> + * when it's decided that it will be calling stack_depot_save() later. This is
> + * recommended for e.g. modules initialized later in the boot process, when
> + * slab_is_available() is true.
>   *
>   * The alternative is to select STACKDEPOT_ALWAYS_INIT to have stack depot
>   * enabled as part of mm_init(), for subsystems where it's known at compile time
>   * that stack depot will be used.
> + *
> + * Another alternative is to call stack_depot_want_early_init(), when the
> + * decision to use stack depot is taken e.g. when evaluating kernel boot
> + * parameters, which precedes the enablement point in mm_init().
> + *
> + * stack_depot_init() and stack_depot_want_early_init() can be called regardless
> + * of CONFIG_STACKDEPOT and are no-op when disabled. The actual save/fetch/print
> + * functions should only be called from code that makes sure CONFIG_STACKDEPOT
> + * is enabled.
>   */
> +#ifdef CONFIG_STACKDEPOT
>  int stack_depot_init(void);
>
> -#ifdef CONFIG_STACKDEPOT_ALWAYS_INIT
> -static inline int stack_depot_early_init(void) { return stack_depot_init(); }
> +void __init stack_depot_want_early_init(void);
> +
> +/* This is supposed to be called only from mm_init() */
> +int __init stack_depot_early_init(void);
>  #else
> +static inline int stack_depot_init(void) { return 0; }
> +
> +static inline void stack_depot_want_early_init(void) { }
> +
>  static inline int stack_depot_early_init(void) { return 0; }
>  #endif
>
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index bf5ba9af0500..0a5916f1e7a3 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -66,6 +66,9 @@ struct stack_record {
>         unsigned long entries[];        /* Variable-sized array of entries. */
>  };
>
> +static bool __stack_depot_want_early_init __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
> +static bool __stack_depot_early_init_passed __initdata;
> +
>  static void *stack_slabs[STACK_ALLOC_MAX_SLABS];
>
>  static int depot_index;
> @@ -162,38 +165,58 @@ static int __init is_stack_depot_disabled(char *str)
>  }
>  early_param("stack_depot_disable", is_stack_depot_disabled);
>
> -/*
> - * __ref because of memblock_alloc(), which will not be actually called after
> - * the __init code is gone, because at that point slab_is_available() is true
> - */
> -__ref int stack_depot_init(void)
> +void __init stack_depot_want_early_init(void)
> +{
> +       /* Too late to request early init now */
> +       WARN_ON(__stack_depot_early_init_passed);
> +
> +       __stack_depot_want_early_init = true;
> +}
> +
> +int __init stack_depot_early_init(void)
> +{
> +       size_t size;
> +       int i;
> +
> +       /* This is supposed to be called only once, from mm_init() */
> +       if (WARN_ON(__stack_depot_early_init_passed))
> +               return 0;
> +
> +       __stack_depot_early_init_passed = true;
> +
> +       if (!__stack_depot_want_early_init || stack_depot_disable)
> +               return 0;
> +
> +       pr_info("Stack Depot early init allocating hash table with memblock_alloc\n");
> +       size = (STACK_HASH_SIZE * sizeof(struct stack_record *));
> +       stack_table = memblock_alloc(size, SMP_CACHE_BYTES);
> +
> +       if (!stack_table) {
> +               pr_err("Stack Depot hash table allocation failed, disabling\n");
> +               stack_depot_disable = true;
> +               return -ENOMEM;
> +       }
> +
> +       return 0;
> +}
> +
> +int stack_depot_init(void)
>  {
>         static DEFINE_MUTEX(stack_depot_init_mutex);
> +       int ret = 0;
>
>         mutex_lock(&stack_depot_init_mutex);
>         if (!stack_depot_disable && !stack_table) {
> -               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 {
> -                       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++)
> -                               stack_table[i] = NULL;
> -               } else {
> +               pr_info("Stack Depot allocating hash table with kvcalloc\n");
> +               stack_table = kvcalloc(STACK_HASH_SIZE, sizeof(struct stack_record *), GFP_KERNEL);
> +               if (!stack_table) {
>                         pr_err("Stack Depot hash table allocation failed, disabling\n");
>                         stack_depot_disable = true;
> -                       mutex_unlock(&stack_depot_init_mutex);
> -                       return -ENOMEM;
> +                       ret = -ENOMEM;
>                 }
>         }
>         mutex_unlock(&stack_depot_init_mutex);
> -       return 0;
> +       return ret;
>  }
>  EXPORT_SYMBOL_GPL(stack_depot_init);
>
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 99e360df9465..4313f8212a83 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -42,7 +42,12 @@ static void init_early_allocated_pages(void);
>
>  static int __init early_page_owner_param(char *buf)
>  {
> -       return kstrtobool(buf, &page_owner_enabled);
> +       int ret = kstrtobool(buf, &page_owner_enabled);
> +
> +       if (page_owner_enabled)
> +               stack_depot_want_early_init();
> +
> +       return ret;
>  }
>  early_param("page_owner", early_page_owner_param);
>
> @@ -80,8 +85,6 @@ static __init void init_page_owner(void)
>         if (!page_owner_enabled)
>                 return;
>
> -       stack_depot_init();
> -
>         register_dummy_stack();
>         register_failure_stack();
>         register_early_stack();
> --
> 2.35.1
>
>