lib/alloc_tag.c

// SPDX-License-Identifier: GPL-2.0-only
#include <linux/alloc_tag.h>
#include <linux/execmem.h>
#include <linux/fs.h>
#include <linux/gfp.h>
#include <linux/kallsyms.h>
#include <linux/module.h>
#include <linux/page_ext.h>
#include <linux/pgalloc_tag.h>
#include <linux/proc_fs.h>
#include <linux/rcupdate.h>
#include <linux/seq_buf.h>
#include <linux/seq_file.h>
#include <linux/string_choices.h>
#include <linux/vmalloc.h>
#include <linux/kmemleak.h>

#define ALLOCINFO_FILE_NAME		"allocinfo"
#define MODULE_ALLOC_TAG_VMAP_SIZE	(100000UL * sizeof(struct alloc_tag))
#define SECTION_START(NAME)		(CODETAG_SECTION_START_PREFIX NAME)
#define SECTION_STOP(NAME)		(CODETAG_SECTION_STOP_PREFIX NAME)

#ifdef CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT
static bool mem_profiling_support = true;
#else
static bool mem_profiling_support;
#endif

/*
 * Memory allocation profiling is permanently disabled and cannot be enabled.
 * Must be called after setup_early_mem_profiling().
 */
bool mem_alloc_profiling_permanently_disabled(void)
{
	return !mem_profiling_support;
}

static struct codetag_type *alloc_tag_cttype;

#ifdef CONFIG_ARCH_MODULE_NEEDS_WEAK_PER_CPU
DEFINE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag);
EXPORT_SYMBOL(_shared_alloc_tag);
#endif

DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
			mem_alloc_profiling_key);
EXPORT_SYMBOL(mem_alloc_profiling_key);

DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);

struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };
unsigned long alloc_tag_ref_mask;
int alloc_tag_ref_offs;

struct allocinfo_private {
	struct codetag_iterator iter;
	struct codetag_iterator reported_iter;
	bool print_header;
};

static void *allocinfo_start(struct seq_file *m, loff_t *pos)
{
	struct allocinfo_private *priv;
	loff_t node = *pos;

	priv = (struct allocinfo_private *)m->private;
	codetag_lock_module_list(alloc_tag_cttype);
	if (node == 0) {
		priv->print_header = true;
		priv->iter = codetag_get_ct_iter(alloc_tag_cttype);
	} else {
		priv->iter = priv->reported_iter;
	}
	codetag_next_ct(&priv->iter);
	return priv->iter.ct ? priv : NULL;
}

static void *allocinfo_next(struct seq_file *m, void *arg, loff_t *pos)
{
	struct allocinfo_private *priv = (struct allocinfo_private *)arg;
	struct codetag *ct;

	priv->reported_iter = priv->iter;
	ct = codetag_next_ct(&priv->iter);
	(*pos)++;
	if (!ct)
		return NULL;

	return priv;
}

static void allocinfo_stop(struct seq_file *m, void *arg)
{
	codetag_unlock_module_list(alloc_tag_cttype);
}

static void print_allocinfo_header(struct seq_buf *buf)
{
	/* Output format version, so we can change it. */
	seq_buf_printf(buf, "allocinfo - version: 2.0\n");
	seq_buf_printf(buf, "#     <size>  <calls> <tag info>\n");
}

static void alloc_tag_to_text(struct seq_buf *out, struct codetag *ct)
{
	struct alloc_tag *tag = ct_to_alloc_tag(ct);
	struct alloc_tag_counters counter = alloc_tag_read(tag);
	s64 bytes = counter.bytes;

	seq_buf_printf(out, "%12lli %8llu ", bytes, counter.calls);
	codetag_to_text(out, ct);
	if (unlikely(alloc_tag_is_inaccurate(tag)))
		seq_buf_printf(out, " accurate:no");
	seq_buf_putc(out, ' ');
	seq_buf_putc(out, '\n');
}

static int allocinfo_show(struct seq_file *m, void *arg)
{
	struct allocinfo_private *priv = (struct allocinfo_private *)arg;
	char *bufp;
	size_t n = seq_get_buf(m, &bufp);
	struct seq_buf buf;

	seq_buf_init(&buf, bufp, n);
	if (priv->print_header) {
		print_allocinfo_header(&buf);
		priv->print_header = false;
	}
	alloc_tag_to_text(&buf, priv->iter.ct);
	seq_commit(m, seq_buf_used(&buf));
	return 0;
}

static const struct seq_operations allocinfo_seq_op = {
	.start	= allocinfo_start,
	.next	= allocinfo_next,
	.stop	= allocinfo_stop,
	.show	= allocinfo_show,
};

size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sleep)
{
	struct codetag_iterator iter;
	struct codetag *ct;
	struct codetag_bytes n;
	unsigned int i, nr = 0;

	if (IS_ERR_OR_NULL(alloc_tag_cttype))
		return 0;

	if (can_sleep)
		codetag_lock_module_list(alloc_tag_cttype);
	else if (!codetag_trylock_module_list(alloc_tag_cttype))
		return 0;

	iter = codetag_get_ct_iter(alloc_tag_cttype);
	while ((ct = codetag_next_ct(&iter))) {
		struct alloc_tag_counters counter = alloc_tag_read(ct_to_alloc_tag(ct));

		n.ct	= ct;
		n.bytes = counter.bytes;

		for (i = 0; i < nr; i++)
			if (n.bytes > tags[i].bytes)
				break;

		if (i < count) {
			nr -= nr == count;
			memmove(&tags[i + 1],
				&tags[i],
				sizeof(tags[0]) * (nr - i));
			nr++;
			tags[i] = n;
		}
	}

	codetag_unlock_module_list(alloc_tag_cttype);

	return nr;
}

void pgalloc_tag_split(struct folio *folio, int old_order, int new_order)
{
	int i;
	struct alloc_tag *tag;
	unsigned int nr_pages = 1 << new_order;

	if (!mem_alloc_profiling_enabled())
		return;

	tag = __pgalloc_tag_get(&folio->page);
	if (!tag)
		return;

	for (i = nr_pages; i < (1 << old_order); i += nr_pages) {
		union pgtag_ref_handle handle;
		union codetag_ref ref;

		if (get_page_tag_ref(folio_page(folio, i), &ref, &handle)) {
			/* Set new reference to point to the original tag */
			alloc_tag_ref_set(&ref, tag);
			update_page_tag_ref(handle, &ref);
			put_page_tag_ref(handle);
		}
	}
}

void pgalloc_tag_swap(struct folio *new, struct folio *old)
{
	union pgtag_ref_handle handle_old, handle_new;
	union codetag_ref ref_old, ref_new;
	struct alloc_tag *tag_old, *tag_new;

	if (!mem_alloc_profiling_enabled())
		return;

	tag_old = __pgalloc_tag_get(&old->page);
	if (!tag_old)
		return;
	tag_new = __pgalloc_tag_get(&new->page);
	if (!tag_new)
		return;

	if (!get_page_tag_ref(&old->page, &ref_old, &handle_old))
		return;
	if (!get_page_tag_ref(&new->page, &ref_new, &handle_new)) {
		put_page_tag_ref(handle_old);
		return;
	}

	/*
	 * Clear tag references to avoid debug warning when using
	 * __alloc_tag_ref_set() with non-empty reference.
	 */
	set_codetag_empty(&ref_old);
	set_codetag_empty(&ref_new);

	/* swap tags */
	__alloc_tag_ref_set(&ref_old, tag_new);
	update_page_tag_ref(handle_old, &ref_old);
	__alloc_tag_ref_set(&ref_new, tag_old);
	update_page_tag_ref(handle_new, &ref_new);

	put_page_tag_ref(handle_old);
	put_page_tag_ref(handle_new);
}

static void shutdown_mem_profiling(bool remove_file)
{
	if (mem_alloc_profiling_enabled())
		static_branch_disable(&mem_alloc_profiling_key);

	if (!mem_profiling_support)
		return;

	if (remove_file)
		remove_proc_entry(ALLOCINFO_FILE_NAME, NULL);
	mem_profiling_support = false;
}

void __init alloc_tag_sec_init(void)
{
	struct alloc_tag *last_codetag;

	if (!mem_profiling_support)
		return;

	if (!static_key_enabled(&mem_profiling_compressed))
		return;

	kernel_tags.first_tag = (struct alloc_tag *)kallsyms_lookup_name(
					SECTION_START(ALLOC_TAG_SECTION_NAME));
	last_codetag = (struct alloc_tag *)kallsyms_lookup_name(
					SECTION_STOP(ALLOC_TAG_SECTION_NAME));
	kernel_tags.count = last_codetag - kernel_tags.first_tag;

	/* Check if kernel tags fit into page flags */
	if (kernel_tags.count > (1UL << NR_UNUSED_PAGEFLAG_BITS)) {
		shutdown_mem_profiling(false); /* allocinfo file does not exist yet */
		pr_err("%lu allocation tags cannot be references using %d available page flag bits. Memory allocation profiling is disabled!\n",
			kernel_tags.count, NR_UNUSED_PAGEFLAG_BITS);
		return;
	}

	alloc_tag_ref_offs = (LRU_REFS_PGOFF - NR_UNUSED_PAGEFLAG_BITS);
	alloc_tag_ref_mask = ((1UL << NR_UNUSED_PAGEFLAG_BITS) - 1);
	pr_debug("Memory allocation profiling compression is using %d page flag bits!\n",
		 NR_UNUSED_PAGEFLAG_BITS);
}

#ifdef CONFIG_MODULES

static struct maple_tree mod_area_mt = MTREE_INIT(mod_area_mt, MT_FLAGS_ALLOC_RANGE);
static struct vm_struct *vm_module_tags;
/* A dummy object used to indicate an unloaded module */
static struct module unloaded_mod;
/* A dummy object used to indicate a module prepended area */
static struct module prepend_mod;

struct alloc_tag_module_section module_tags;

static inline unsigned long alloc_tag_align(unsigned long val)
{
	if (!static_key_enabled(&mem_profiling_compressed)) {
		/* No alignment requirements when we are not indexing the tags */
		return val;
	}

	if (val % sizeof(struct alloc_tag) == 0)
		return val;
	return ((val / sizeof(struct alloc_tag)) + 1) * sizeof(struct alloc_tag);
}

static bool ensure_alignment(unsigned long align, unsigned int *prepend)
{
	if (!static_key_enabled(&mem_profiling_compressed)) {
		/* No alignment requirements when we are not indexing the tags */
		return true;
	}

	/*
	 * If alloc_tag size is not a multiple of required alignment, tag
	 * indexing does not work.
	 */
	if (!IS_ALIGNED(sizeof(struct alloc_tag), align))
		return false;

	/* Ensure prepend consumes multiple of alloc_tag-sized blocks */
	if (*prepend)
		*prepend = alloc_tag_align(*prepend);

	return true;
}

static inline bool tags_addressable(void)
{
	unsigned long tag_idx_count;

	if (!static_key_enabled(&mem_profiling_compressed))
		return true; /* with page_ext tags are always addressable */

	tag_idx_count = CODETAG_ID_FIRST + kernel_tags.count +
			module_tags.size / sizeof(struct alloc_tag);

	return tag_idx_count < (1UL << NR_UNUSED_PAGEFLAG_BITS);
}

static bool needs_section_mem(struct module *mod, unsigned long size)
{
	if (!mem_profiling_support)
		return false;

	return size >= sizeof(struct alloc_tag);
}

static bool clean_unused_counters(struct alloc_tag *start_tag,
				  struct alloc_tag *end_tag)
{
	struct alloc_tag *tag;
	bool ret = true;

	for (tag = start_tag; tag <= end_tag; tag++) {
		struct alloc_tag_counters counter;

		if (!tag->counters)
			continue;

		counter = alloc_tag_read(tag);
		if (!counter.bytes) {
			free_percpu(tag->counters);
			tag->counters = NULL;
		} else {
			ret = false;
		}
	}

	return ret;
}

/* Called with mod_area_mt locked */
static void clean_unused_module_areas_locked(void)
{
	MA_STATE(mas, &mod_area_mt, 0, module_tags.size);
	struct module *val;

	mas_for_each(&mas, val, module_tags.size) {
		struct alloc_tag *start_tag;
		struct alloc_tag *end_tag;

		if (val != &unloaded_mod)
			continue;

		/* Release area if all tags are unused */
		start_tag = (struct alloc_tag *)(module_tags.start_addr + mas.index);
		end_tag = (struct alloc_tag *)(module_tags.start_addr + mas.last);
		if (clean_unused_counters(start_tag, end_tag))
			mas_erase(&mas);
	}
}

/* Called with mod_area_mt locked */
static bool find_aligned_area(struct ma_state *mas, unsigned long section_size,
			      unsigned long size, unsigned int prepend, unsigned long align)
{
	bool cleanup_done = false;

repeat:
	/* Try finding exact size and hope the start is aligned */
	if (!mas_empty_area(mas, 0, section_size - 1, prepend + size)) {
		if (IS_ALIGNED(mas->index + prepend, align))
			return true;

		/* Try finding larger area to align later */
		mas_reset(mas);
		if (!mas_empty_area(mas, 0, section_size - 1,
				    size + prepend + align - 1))
			return true;
	}

	/* No free area, try cleanup stale data and repeat the search once */
	if (!cleanup_done) {
		clean_unused_module_areas_locked();
		cleanup_done = true;
		mas_reset(mas);
		goto repeat;
	}

	return false;
}

static int vm_module_tags_populate(void)
{
	unsigned long phys_end = ALIGN_DOWN(module_tags.start_addr, PAGE_SIZE) +
				 (vm_module_tags->nr_pages << PAGE_SHIFT);
	unsigned long new_end = module_tags.start_addr + module_tags.size;

	if (phys_end < new_end) {
		struct page **next_page = vm_module_tags->pages + vm_module_tags->nr_pages;
		unsigned long old_shadow_end = ALIGN(phys_end, MODULE_ALIGN);
		unsigned long new_shadow_end = ALIGN(new_end, MODULE_ALIGN);
		unsigned long more_pages;
		unsigned long nr = 0;

		more_pages = ALIGN(new_end - phys_end, PAGE_SIZE) >> PAGE_SHIFT;
		while (nr < more_pages) {
			unsigned long allocated;

			allocated = alloc_pages_bulk_node(GFP_KERNEL | __GFP_NOWARN,
				NUMA_NO_NODE, more_pages - nr, next_page + nr);

			if (!allocated)
				break;
			nr += allocated;
		}

		if (nr < more_pages ||
		    vmap_pages_range(phys_end, phys_end + (nr << PAGE_SHIFT), PAGE_KERNEL,
				     next_page, PAGE_SHIFT) < 0) {
			release_pages_arg arg = { .pages = next_page };

			/* Clean up and error out */
			release_pages(arg, nr);
			return -ENOMEM;
		}

		vm_module_tags->nr_pages += nr;

		/*
		 * Kasan allocates 1 byte of shadow for every 8 bytes of data.
		 * When kasan_alloc_module_shadow allocates shadow memory,
		 * its unit of allocation is a page.
		 * Therefore, here we need to align to MODULE_ALIGN.
		 */
		if (old_shadow_end < new_shadow_end)
			kasan_alloc_module_shadow((void *)old_shadow_end,
						  new_shadow_end - old_shadow_end,
						  GFP_KERNEL);
	}

	/*
	 * Mark the pages as accessible, now that they are mapped.
	 * With hardware tag-based KASAN, marking is skipped for
	 * non-VM_ALLOC mappings, see __kasan_unpoison_vmalloc().
	 */
	kasan_unpoison_vmalloc((void *)module_tags.start_addr,
				new_end - module_tags.start_addr,
				KASAN_VMALLOC_PROT_NORMAL);

	return 0;
}

static void *reserve_module_tags(struct module *mod, unsigned long size,
				 unsigned int prepend, unsigned long align)
{
	unsigned long section_size = module_tags.end_addr - module_tags.start_addr;
	MA_STATE(mas, &mod_area_mt, 0, section_size - 1);
	unsigned long offset;
	void *ret = NULL;

	/* If no tags return error */
	if (size < sizeof(struct alloc_tag))
		return ERR_PTR(-EINVAL);

	/*
	 * align is always power of 2, so we can use IS_ALIGNED and ALIGN.
	 * align 0 or 1 means no alignment, to simplify set to 1.
	 */
	if (!align)
		align = 1;

	if (!ensure_alignment(align, &prepend)) {
		shutdown_mem_profiling(true);
		pr_err("%s: alignment %lu is incompatible with allocation tag indexing. Memory allocation profiling is disabled!\n",
			mod->name, align);
		return ERR_PTR(-EINVAL);
	}

	mas_lock(&mas);
	if (!find_aligned_area(&mas, section_size, size, prepend, align)) {
		ret = ERR_PTR(-ENOMEM);
		goto unlock;
	}

	/* Mark found area as reserved */
	offset = mas.index;
	offset += prepend;
	offset = ALIGN(offset, align);
	if (offset != mas.index) {
		unsigned long pad_start = mas.index;

		mas.last = offset - 1;
		mas_store(&mas, &prepend_mod);
		if (mas_is_err(&mas)) {
			ret = ERR_PTR(xa_err(mas.node));
			goto unlock;
		}
		mas.index = offset;
		mas.last = offset + size - 1;
		mas_store(&mas, mod);
		if (mas_is_err(&mas)) {
			mas.index = pad_start;
			mas_erase(&mas);
			ret = ERR_PTR(xa_err(mas.node));
		}
	} else {
		mas.last = offset + size - 1;
		mas_store(&mas, mod);
		if (mas_is_err(&mas))
			ret = ERR_PTR(xa_err(mas.node));
	}
unlock:
	mas_unlock(&mas);

	if (IS_ERR(ret))
		return ret;

	if (module_tags.size < offset + size) {
		int grow_res;

		module_tags.size = offset + size;
		if (mem_alloc_profiling_enabled() && !tags_addressable()) {
			shutdown_mem_profiling(true);
			pr_warn("With module %s there are too many tags to fit in %d page flag bits. Memory allocation profiling is disabled!\n",
				mod->name, NR_UNUSED_PAGEFLAG_BITS);
		}

		grow_res = vm_module_tags_populate();
		if (grow_res) {
			shutdown_mem_profiling(true);
			pr_err("Failed to allocate memory for allocation tags in the module %s. Memory allocation profiling is disabled!\n",
			       mod->name);
			return ERR_PTR(grow_res);
		}
	}

	return (struct alloc_tag *)(module_tags.start_addr + offset);
}

static void release_module_tags(struct module *mod, bool used)
{
	MA_STATE(mas, &mod_area_mt, module_tags.size, module_tags.size);
	struct alloc_tag *start_tag;
	struct alloc_tag *end_tag;
	struct module *val;

	mas_lock(&mas);
	mas_for_each_rev(&mas, val, 0)
		if (val == mod)
			break;

	if (!val) /* module not found */
		goto out;

	if (!used)
		goto release_area;

	start_tag = (struct alloc_tag *)(module_tags.start_addr + mas.index);
	end_tag = (struct alloc_tag *)(module_tags.start_addr + mas.last);
	if (!clean_unused_counters(start_tag, end_tag)) {
		struct alloc_tag *tag;

		for (tag = start_tag; tag <= end_tag; tag++) {
			struct alloc_tag_counters counter;

			if (!tag->counters)
				continue;

			counter = alloc_tag_read(tag);
			pr_info("%s:%u module %s func:%s has %llu allocated at module unload\n",
				tag->ct.filename, tag->ct.lineno, tag->ct.modname,
				tag->ct.function, counter.bytes);
		}
	} else {
		used = false;
	}
release_area:
	mas_store(&mas, used ? &unloaded_mod : NULL);
	val = mas_prev_range(&mas, 0);
	if (val == &prepend_mod)
		mas_store(&mas, NULL);
out:
	mas_unlock(&mas);
}

static int load_module(struct module *mod, struct codetag *start, struct codetag *stop)
{
	/* Allocate module alloc_tag percpu counters */
	struct alloc_tag *start_tag;
	struct alloc_tag *stop_tag;
	struct alloc_tag *tag;

	/* percpu counters for core allocations are already statically allocated */
	if (!mod)
		return 0;

	start_tag = ct_to_alloc_tag(start);
	stop_tag = ct_to_alloc_tag(stop);
	for (tag = start_tag; tag < stop_tag; tag++) {
		WARN_ON(tag->counters);
		tag->counters = alloc_percpu(struct alloc_tag_counters);
		if (!tag->counters) {
			while (--tag >= start_tag) {
				free_percpu(tag->counters);
				tag->counters = NULL;
			}
			pr_err("Failed to allocate memory for allocation tag percpu counters in the module %s\n",
			       mod->name);
			return -ENOMEM;
		}

		/*
		 * Avoid a kmemleak false positive. The pointer to the counters is stored
		 * in the alloc_tag section of the module and cannot be directly accessed.
		 */
		kmemleak_ignore_percpu(tag->counters);
	}
	return 0;
}

static void replace_module(struct module *mod, struct module *new_mod)
{
	MA_STATE(mas, &mod_area_mt, 0, module_tags.size);
	struct module *val;

	mas_lock(&mas);
	mas_for_each(&mas, val, module_tags.size) {
		if (val != mod)
			continue;

		mas_store_gfp(&mas, new_mod, GFP_KERNEL);
		break;
	}
	mas_unlock(&mas);
}

static int __init alloc_mod_tags_mem(void)
{
	/* Map space to copy allocation tags */
	vm_module_tags = execmem_vmap(MODULE_ALLOC_TAG_VMAP_SIZE);
	if (!vm_module_tags) {
		pr_err("Failed to map %lu bytes for module allocation tags\n",
			MODULE_ALLOC_TAG_VMAP_SIZE);
		module_tags.start_addr = 0;
		return -ENOMEM;
	}

	vm_module_tags->pages = kmalloc_objs(struct page *,
					     get_vm_area_size(vm_module_tags) >> PAGE_SHIFT,
					     GFP_KERNEL | __GFP_ZERO);
	if (!vm_module_tags->pages) {
		free_vm_area(vm_module_tags);
		return -ENOMEM;
	}

	module_tags.start_addr = (unsigned long)vm_module_tags->addr;
	module_tags.end_addr = module_tags.start_addr + MODULE_ALLOC_TAG_VMAP_SIZE;
	/* Ensure the base is alloc_tag aligned when required for indexing */
	module_tags.start_addr = alloc_tag_align(module_tags.start_addr);

	return 0;
}

static void __init free_mod_tags_mem(void)
{
	release_pages_arg arg = { .pages = vm_module_tags->pages };

	module_tags.start_addr = 0;
	release_pages(arg, vm_module_tags->nr_pages);
	kfree(vm_module_tags->pages);
	free_vm_area(vm_module_tags);
}

#else /* CONFIG_MODULES */

static inline int alloc_mod_tags_mem(void) { return 0; }
static inline void free_mod_tags_mem(void) {}

#endif /* CONFIG_MODULES */

/* See: Documentation/mm/allocation-profiling.rst */
static int __init setup_early_mem_profiling(char *str)
{
	bool compressed = false;
	bool enable;

	if (!str || !str[0])
		return -EINVAL;

	if (!strncmp(str, "never", 5)) {
		enable = false;
		mem_profiling_support = false;
		pr_info("Memory allocation profiling is disabled!\n");
	} else {
		char *token = strsep(&str, ",");

		if (kstrtobool(token, &enable))
			return -EINVAL;

		if (str) {

			if (strcmp(str, "compressed"))
				return -EINVAL;

			compressed = true;
		}
		mem_profiling_support = true;
		pr_info("Memory allocation profiling is enabled %s compression and is turned %s!\n",
			compressed ? "with" : "without", str_on_off(enable));
	}

	if (enable != mem_alloc_profiling_enabled()) {
		if (enable)
			static_branch_enable(&mem_alloc_profiling_key);
		else
			static_branch_disable(&mem_alloc_profiling_key);
	}
	if (compressed != static_key_enabled(&mem_profiling_compressed)) {
		if (compressed)
			static_branch_enable(&mem_profiling_compressed);
		else
			static_branch_disable(&mem_profiling_compressed);
	}

	return 0;
}
early_param("sysctl.vm.mem_profiling", setup_early_mem_profiling);

static __init bool need_page_alloc_tagging(void)
{
	if (static_key_enabled(&mem_profiling_compressed))
		return false;

	return mem_profiling_support;
}

#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
/*
 * Track page allocations before page_ext is initialized.
 * Some pages are allocated before page_ext becomes available, leaving
 * their codetag uninitialized. Track these early PFNs so we can clear
 * their codetag refs later to avoid warnings when they are freed.
 *
 * Each page is cast to a pfn_pool: the first few bytes hold metadata
 * (next pointer and slot count), the remainder stores PFNs.
 */
struct pfn_pool {
	struct pfn_pool *next;
	atomic_t count;
	unsigned long pfns[];
};

#define PFN_POOL_SIZE			((PAGE_SIZE - offsetof(struct pfn_pool, pfns)) / \
					 sizeof(unsigned long))

/*
 * Skip early PFN recording for a page allocation.  Reuses the
 * %__GFP_NO_OBJ_EXT bit.  Used by __alloc_tag_add_early_pfn() to avoid
 * recursion when allocating pages for the early PFN tracking list
 * itself.
 *
 * Codetags of the pages allocated with __GFP_NO_CODETAG should be
 * cleared (via clear_page_tag_ref()) before freeing the pages to prevent
 * alloc_tag_sub_check() from triggering a warning.
 */
#define __GFP_NO_CODETAG		__GFP_NO_OBJ_EXT

static struct pfn_pool *current_pfn_pool __initdata;

static void __init __alloc_tag_add_early_pfn(unsigned long pfn)
{
	struct pfn_pool *pool;
	int idx;

	do {
		pool = READ_ONCE(current_pfn_pool);
		if (!pool || atomic_read(&pool->count) >= PFN_POOL_SIZE) {
			struct page *new_page = alloc_page(__GFP_HIGH | __GFP_NO_CODETAG);
			struct pfn_pool *new;

			if (!new_page) {
				pr_warn_once("early PFN tracking page allocation failed\n");
				return;
			}
			new = page_address(new_page);
			new->next = pool;
			atomic_set(&new->count, 0);
			if (cmpxchg(&current_pfn_pool, pool, new) != pool) {
				clear_page_tag_ref(new_page);
				__free_page(new_page);
				continue;
			}
			pool = new;
		}
		idx = atomic_read(&pool->count);
		if (idx >= PFN_POOL_SIZE)
			continue;
		if (atomic_cmpxchg(&pool->count, idx, idx + 1) == idx)
			break;
	} while (1);

	pool->pfns[idx] = pfn;
}

typedef void alloc_tag_add_func(unsigned long pfn);
static alloc_tag_add_func __rcu *alloc_tag_add_early_pfn_ptr __refdata =
	RCU_INITIALIZER(__alloc_tag_add_early_pfn);

void alloc_tag_add_early_pfn(unsigned long pfn, gfp_t gfp_flags)
{
	alloc_tag_add_func *alloc_tag_add;

	if (static_key_enabled(&mem_profiling_compressed))
		return;

	/* Skip allocations for the tracking list itself to avoid recursion. */
	if (gfp_flags & __GFP_NO_CODETAG)
		return;

	rcu_read_lock();
	alloc_tag_add = rcu_dereference(alloc_tag_add_early_pfn_ptr);
	if (alloc_tag_add)
		alloc_tag_add(pfn);
	rcu_read_unlock();
}

static void __init clear_early_alloc_pfn_tag_refs(void)
{
	struct pfn_pool *pool, *next;
	struct page *page;
	int i;

	if (static_key_enabled(&mem_profiling_compressed))
		return;

	rcu_assign_pointer(alloc_tag_add_early_pfn_ptr, NULL);
	/* Make sure we are not racing with __alloc_tag_add_early_pfn() */
	synchronize_rcu();

	for (pool = current_pfn_pool; pool; pool = next) {
		int nr_pfns = atomic_read(&pool->count);

		for (i = 0; i < nr_pfns; i++) {
			unsigned long pfn = pool->pfns[i];

			if (pfn_valid(pfn)) {
				union pgtag_ref_handle handle;
				union codetag_ref ref;

				if (get_page_tag_ref(pfn_to_page(pfn), &ref, &handle)) {
					/*
					 * An early-allocated page could be freed and reallocated
					 * after its page_ext is initialized but before we clear it.
					 * In that case, it already has a valid tag set.
					 * We should not overwrite that valid tag
					 * with CODETAG_EMPTY.
					 *
					 * Note: there is still a small race window between checking
					 * ref.ct and calling set_codetag_empty(). We accept this
					 * race as it's unlikely and the extra complexity of atomic
					 * cmpxchg is not worth it for this debug-only code path.
					 */
					if (ref.ct) {
						put_page_tag_ref(handle);
						continue;
					}

					set_codetag_empty(&ref);
					update_page_tag_ref(handle, &ref);
					put_page_tag_ref(handle);
				}
			}
		}

		next = pool->next;
		page = virt_to_page(pool);
		clear_page_tag_ref(page);
		__free_page(page);
	}
}
#else /* !CONFIG_MEM_ALLOC_PROFILING_DEBUG */
static inline void __init clear_early_alloc_pfn_tag_refs(void) {}
#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */

static __init void init_page_alloc_tagging(void)
{
	clear_early_alloc_pfn_tag_refs();
}

struct page_ext_operations page_alloc_tagging_ops = {
	.size = sizeof(union codetag_ref),
	.need = need_page_alloc_tagging,
	.init = init_page_alloc_tagging,
};
EXPORT_SYMBOL(page_alloc_tagging_ops);

#ifdef CONFIG_SYSCTL
/*
 * Not using proc_do_static_key() directly to prevent enabling profiling
 * after it was shut down.
 */
static int proc_mem_profiling_handler(const struct ctl_table *table, int write,
				      void *buffer, size_t *lenp, loff_t *ppos)
{
	if (write) {
		/*
		 * Call from do_sysctl_args() which is a no-op since the same
		 * value was already set by setup_early_mem_profiling.
		 * Return success to avoid warnings from do_sysctl_args().
		 */
		if (!current->mm)
			return 0;

#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
		/* User can't toggle profiling while debugging */
		return -EACCES;
#endif
		if (!mem_profiling_support)
			return -EINVAL;
	}

	return proc_do_static_key(table, write, buffer, lenp, ppos);
}


static const struct ctl_table memory_allocation_profiling_sysctls[] = {
	{
		.procname	= "mem_profiling",
		.data		= &mem_alloc_profiling_key,
		.mode		= 0644,
		.proc_handler	= proc_mem_profiling_handler,
	},
};

static void __init sysctl_init(void)
{
	register_sysctl_init("vm", memory_allocation_profiling_sysctls);
}
#else /* CONFIG_SYSCTL */
static inline void sysctl_init(void) {}
#endif /* CONFIG_SYSCTL */

static int __init alloc_tag_init(void)
{
	const struct codetag_type_desc desc = {
		.section		= ALLOC_TAG_SECTION_NAME,
		.tag_size		= sizeof(struct alloc_tag),
#ifdef CONFIG_MODULES
		.needs_section_mem	= needs_section_mem,
		.alloc_section_mem	= reserve_module_tags,
		.free_section_mem	= release_module_tags,
		.module_load		= load_module,
		.module_replaced	= replace_module,
#endif
	};
	int res;

	sysctl_init();

	if (!mem_profiling_support) {
		pr_info("Memory allocation profiling is not supported!\n");
		return 0;
	}

	if (!proc_create_seq_private(ALLOCINFO_FILE_NAME, 0400, NULL, &allocinfo_seq_op,
				     sizeof(struct allocinfo_private), NULL)) {
		pr_err("Failed to create %s file\n", ALLOCINFO_FILE_NAME);
		shutdown_mem_profiling(false);
		return -ENOMEM;
	}

	res = alloc_mod_tags_mem();
	if (res) {
		pr_err("Failed to reserve address space for module tags, errno = %d\n", res);
		shutdown_mem_profiling(true);
		return res;
	}

	alloc_tag_cttype = codetag_register_type(&desc);
	if (IS_ERR(alloc_tag_cttype)) {
		pr_err("Allocation tags registration failed, errno = %pe\n", alloc_tag_cttype);
		free_mod_tags_mem();
		shutdown_mem_profiling(true);
		return PTR_ERR(alloc_tag_cttype);
	}

	return 0;
}
module_init(alloc_tag_init);