mm/slab_common.c - kernel/common - Git at Google

 // SPDX-License-Identifier: GPL-2.0
 /*
  * Slab allocator functions that are independent of the allocator strategy
  *
  * (C) 2012 Christoph Lameter <cl@linux.com>
  */
 #include <linux/slab.h>

 #include <linux/mm.h>
 #include <linux/poison.h>
 #include <linux/interrupt.h>
 #include <linux/memory.h>
 #include <linux/cache.h>
 #include <linux/compiler.h>
 #include <linux/kfence.h>
 #include <linux/module.h>
 #include <linux/cpu.h>
 #include <linux/uaccess.h>
 #include <linux/seq_file.h>
 #include <linux/proc_fs.h>
 #include <linux/debugfs.h>
 #include <linux/kasan.h>
 #include <asm/cacheflush.h>
 #include <asm/tlbflush.h>
 #include <asm/page.h>
 #include <linux/memcontrol.h>

 #define CREATE_TRACE_POINTS
 #include <trace/events/kmem.h>

 #include "internal.h"

 #include "slab.h"

 enum slab_state slab_state;
 LIST_HEAD(slab_caches);
 DEFINE_MUTEX(slab_mutex);
 struct kmem_cache *kmem_cache;

 #ifdef CONFIG_HARDENED_USERCOPY
 bool usercopy_fallback __ro_after_init =
 		IS_ENABLED(CONFIG_HARDENED_USERCOPY_FALLBACK);
 module_param(usercopy_fallback, bool, 0400);
 MODULE_PARM_DESC(usercopy_fallback,
 		"WARN instead of reject usercopy whitelist violations");
 #endif

 static LIST_HEAD(slab_caches_to_rcu_destroy);
 static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work);
 static DECLARE_WORK(slab_caches_to_rcu_destroy_work,
 		    slab_caches_to_rcu_destroy_workfn);

 /*
  * Set of flags that will prevent slab merging
  */
 #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \
 		SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \
 		SLAB_FAILSLAB | kasan_never_merge())

 #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \
 			 SLAB_CACHE_DMA32 | SLAB_ACCOUNT)

 /*
  * Merge control. If this is set then no merging of slab caches will occur.
  */
 static bool slab_nomerge = !IS_ENABLED(CONFIG_SLAB_MERGE_DEFAULT);

 static int __init setup_slab_nomerge(char *str)
 {
 	slab_nomerge = true;
 	return 1;
 }

 static int __init setup_slab_merge(char *str)
 {
 	slab_nomerge = false;
 	return 1;
 }

 #ifdef CONFIG_SLUB
 __setup_param("slub_nomerge", slub_nomerge, setup_slab_nomerge, 0);
 __setup_param("slub_merge", slub_merge, setup_slab_merge, 0);
 #endif

 __setup("slab_nomerge", setup_slab_nomerge);
 __setup("slab_merge", setup_slab_merge);

 /*
  * Determine the size of a slab object
  */
 unsigned int kmem_cache_size(struct kmem_cache *s)
 {
 	return s->object_size;
 }
 EXPORT_SYMBOL(kmem_cache_size);

 #ifdef CONFIG_DEBUG_VM
 static int kmem_cache_sanity_check(const char *name, unsigned int size)
 {
 	if (!name || in_interrupt() || size > KMALLOC_MAX_SIZE) {
 		pr_err("kmem_cache_create(%s) integrity check failed\n", name);
 		return -EINVAL;
 	}

 	WARN_ON(strchr(name, ' '));	/* It confuses parsers */
 	return 0;
 }
 #else
 static inline int kmem_cache_sanity_check(const char *name, unsigned int size)
 {
 	return 0;
 }
 #endif

 void __kmem_cache_free_bulk(struct kmem_cache *s, size_t nr, void **p)
 {
 	size_t i;

 	for (i = 0; i < nr; i++) {
 		if (s)
 			kmem_cache_free(s, p[i]);
 		else
 			kfree(p[i]);
 	}
 }

 int __kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t nr,
 								void **p)
 {
 	size_t i;

 	for (i = 0; i < nr; i++) {
 		void *x = p[i] = kmem_cache_alloc(s, flags);
 		if (!x) {
 			__kmem_cache_free_bulk(s, i, p);
 			return 0;
 		}
 	}
 	return i;
 }

 /*
  * Figure out what the alignment of the objects will be given a set of
  * flags, a user specified alignment and the size of the objects.
  */
 static unsigned int calculate_alignment(slab_flags_t flags,
 		unsigned int align, unsigned int size)
 {
 	/*
 	 * If the user wants hardware cache aligned objects then follow that
 	 * suggestion if the object is sufficiently large.
 	 *
 	 * The hardware cache alignment cannot override the specified
 	 * alignment though. If that is greater then use it.
 	 */
 	if (flags & SLAB_HWCACHE_ALIGN) {
 		unsigned int ralign;

 		ralign = cache_line_size();
 		while (size <= ralign / 2)
 			ralign /= 2;
 		align = max(align, ralign);
 	}

 	if (align < ARCH_SLAB_MINALIGN)
 		align = ARCH_SLAB_MINALIGN;

 	return ALIGN(align, sizeof(void *));
 }

 /*
  * Find a mergeable slab cache
  */
 int slab_unmergeable(struct kmem_cache *s)
 {
 	if (slab_nomerge || (s->flags & SLAB_NEVER_MERGE))
 		return 1;

 	if (s->ctor)
 		return 1;

 	if (s->usersize)
 		return 1;

 	/*
 	 * We may have set a slab to be unmergeable during bootstrap.
 	 */
 	if (s->refcount < 0)
 		return 1;

 	return 0;
 }

 struct kmem_cache *find_mergeable(unsigned int size, unsigned int align,
 		slab_flags_t flags, const char *name, void (*ctor)(void *))
 {
 	struct kmem_cache *s;

 	if (slab_nomerge)
 		return NULL;

 	if (ctor)
 		return NULL;

 	size = ALIGN(size, sizeof(void *));
 	align = calculate_alignment(flags, align, size);
 	size = ALIGN(size, align);
 	flags = kmem_cache_flags(size, flags, name);

 	if (flags & SLAB_NEVER_MERGE)
 		return NULL;

 	list_for_each_entry_reverse(s, &slab_caches, list) {
 		if (slab_unmergeable(s))
 			continue;

 		if (size > s->size)
 			continue;

 		if ((flags & SLAB_MERGE_SAME) != (s->flags & SLAB_MERGE_SAME))
 			continue;
 		/*
 		 * Check if alignment is compatible.
 		 * Courtesy of Adrian Drzewiecki
 		 */
 		if ((s->size & ~(align - 1)) != s->size)
 			continue;

 		if (s->size - size >= sizeof(void *))
 			continue;

 		if (IS_ENABLED(CONFIG_SLAB) && align &&
 			(align > s->align || s->align % align))
 			continue;

 		return s;
 	}
 	return NULL;
 }

 static struct kmem_cache *create_cache(const char *name,
 		unsigned int object_size, unsigned int align,
 		slab_flags_t flags, unsigned int useroffset,
 		unsigned int usersize, void (*ctor)(void *),
 		struct kmem_cache *root_cache)
 {
 	struct kmem_cache *s;
 	int err;

 	if (WARN_ON(useroffset + usersize > object_size))
 		useroffset = usersize = 0;

 	err = -ENOMEM;
 	s = kmem_cache_zalloc(kmem_cache, GFP_KERNEL);
 	if (!s)
 		goto out;

 	s->name = name;
 	s->size = s->object_size = object_size;
 	s->align = align;
 	s->ctor = ctor;
 	s->useroffset = useroffset;
 	s->usersize = usersize;

 	err = __kmem_cache_create(s, flags);
 	if (err)
 		goto out_free_cache;

 	s->refcount = 1;
 	list_add(&s->list, &slab_caches);
 out:
 	if (err)
 		return ERR_PTR(err);
 	return s;

 out_free_cache:
 	kmem_cache_free(kmem_cache, s);
 	goto out;
 }

 /**
  * kmem_cache_create_usercopy - Create a cache with a region suitable
  * for copying to userspace
  * @name: A string which is used in /proc/slabinfo to identify this cache.
  * @size: The size of objects to be created in this cache.
  * @align: The required alignment for the objects.
  * @flags: SLAB flags
  * @useroffset: Usercopy region offset
  * @usersize: Usercopy region size
  * @ctor: A constructor for the objects.
  *
  * Cannot be called within a interrupt, but can be interrupted.
  * The @ctor is run when new pages are allocated by the cache.
  *
  * The flags are
  *
  * %SLAB_POISON - Poison the slab with a known test pattern (a5a5a5a5)
  * to catch references to uninitialised memory.
  *
  * %SLAB_RED_ZONE - Insert `Red` zones around the allocated memory to check
  * for buffer overruns.
  *
  * %SLAB_HWCACHE_ALIGN - Align the objects in this cache to a hardware
  * cacheline.  This can be beneficial if you're counting cycles as closely
  * as davem.
  *
  * Return: a pointer to the cache on success, NULL on failure.
  */
 struct kmem_cache *
 kmem_cache_create_usercopy(const char *name,
 		  unsigned int size, unsigned int align,
 		  slab_flags_t flags,
 		  unsigned int useroffset, unsigned int usersize,
 		  void (*ctor)(void *))
 {
 	struct kmem_cache *s = NULL;
 	const char *cache_name;
 	int err;

 #ifdef CONFIG_SLUB_DEBUG
 	/*
 	 * If no slub_debug was enabled globally, the static key is not yet
 	 * enabled by setup_slub_debug(). Enable it if the cache is being
 	 * created with any of the debugging flags passed explicitly.
 	 */
 	if (flags & SLAB_DEBUG_FLAGS)
 		static_branch_enable(&slub_debug_enabled);
 #endif

 	mutex_lock(&slab_mutex);

 	err = kmem_cache_sanity_check(name, size);
 	if (err) {
 		goto out_unlock;
 	}

 	/* Refuse requests with allocator specific flags */
 	if (flags & ~SLAB_FLAGS_PERMITTED) {
 		err = -EINVAL;
 		goto out_unlock;
 	}

 	/*
 	 * Some allocators will constraint the set of valid flags to a subset
 	 * of all flags. We expect them to define CACHE_CREATE_MASK in this
 	 * case, and we'll just provide them with a sanitized version of the
 	 * passed flags.
 	 */
 	flags &= CACHE_CREATE_MASK;

 	/* Fail closed on bad usersize of useroffset values. */
 	if (WARN_ON(!usersize && useroffset) ||
 	    WARN_ON(size < usersize || size - usersize < useroffset))
 		usersize = useroffset = 0;

 	if (!usersize)
 		s = __kmem_cache_alias(name, size, align, flags, ctor);
 	if (s)
 		goto out_unlock;

 	cache_name = kstrdup_const(name, GFP_KERNEL);
 	if (!cache_name) {
 		err = -ENOMEM;
 		goto out_unlock;
 	}

 	s = create_cache(cache_name, size,
 			 calculate_alignment(flags, align, size),
 			 flags, useroffset, usersize, ctor, NULL);
 	if (IS_ERR(s)) {
 		err = PTR_ERR(s);
 		kfree_const(cache_name);
 	}

 out_unlock:
 	mutex_unlock(&slab_mutex);

 	if (err) {
 		if (flags & SLAB_PANIC)
 			panic("%s: Failed to create slab '%s'. Error %d\n",
 				__func__, name, err);
 		else {
 			pr_warn("%s(%s) failed with error %d\n",
 				__func__, name, err);
 			dump_stack();
 		}
 		return NULL;
 	}
 	return s;
 }
 EXPORT_SYMBOL(kmem_cache_create_usercopy);

 /**
  * kmem_cache_create - Create a cache.
  * @name: A string which is used in /proc/slabinfo to identify this cache.
  * @size: The size of objects to be created in this cache.
  * @align: The required alignment for the objects.
  * @flags: SLAB flags
  * @ctor: A constructor for the objects.
  *
  * Cannot be called within a interrupt, but can be interrupted.
  * The @ctor is run when new pages are allocated by the cache.
  *
  * The flags are
  *
  * %SLAB_POISON - Poison the slab with a known test pattern (a5a5a5a5)
  * to catch references to uninitialised memory.
  *
  * %SLAB_RED_ZONE - Insert `Red` zones around the allocated memory to check
  * for buffer overruns.
  *
  * %SLAB_HWCACHE_ALIGN - Align the objects in this cache to a hardware
  * cacheline.  This can be beneficial if you're counting cycles as closely
  * as davem.
  *
  * Return: a pointer to the cache on success, NULL on failure.
  */
 struct kmem_cache *
 kmem_cache_create(const char *name, unsigned int size, unsigned int align,
 		slab_flags_t flags, void (*ctor)(void *))
 {
 	return kmem_cache_create_usercopy(name, size, align, flags, 0, 0,
 					  ctor);
 }
 EXPORT_SYMBOL(kmem_cache_create);

 static void slab_caches_to_rcu_destroy_workfn(struct work_struct *work)
 {
 	LIST_HEAD(to_destroy);
 	struct kmem_cache *s, *s2;

 	/*
 	 * On destruction, SLAB_TYPESAFE_BY_RCU kmem_caches are put on the
 	 * @slab_caches_to_rcu_destroy list.  The slab pages are freed
 	 * through RCU and the associated kmem_cache are dereferenced
 	 * while freeing the pages, so the kmem_caches should be freed only
 	 * after the pending RCU operations are finished.  As rcu_barrier()
 	 * is a pretty slow operation, we batch all pending destructions
 	 * asynchronously.
 	 */
 	mutex_lock(&slab_mutex);
 	list_splice_init(&slab_caches_to_rcu_destroy, &to_destroy);
 	mutex_unlock(&slab_mutex);

 	if (list_empty(&to_destroy))
 		return;

 	rcu_barrier();

 	list_for_each_entry_safe(s, s2, &to_destroy, list) {
 		debugfs_slab_release(s);
 		kfence_shutdown_cache(s);
 #ifdef SLAB_SUPPORTS_SYSFS
 		sysfs_slab_release(s);
 #else
 		slab_kmem_cache_release(s);
 #endif
 	}
 }

 static int shutdown_cache(struct kmem_cache *s)
 {
 	/* free asan quarantined objects */
 	kasan_cache_shutdown(s);

 	if (__kmem_cache_shutdown(s) != 0)
 		return -EBUSY;

 	list_del(&s->list);

 	if (s->flags & SLAB_TYPESAFE_BY_RCU) {
 #ifdef SLAB_SUPPORTS_SYSFS
 		sysfs_slab_unlink(s);
 #endif
 		list_add_tail(&s->list, &slab_caches_to_rcu_destroy);
 		schedule_work(&slab_caches_to_rcu_destroy_work);
 	} else {
 		kfence_shutdown_cache(s);
 		debugfs_slab_release(s);
 #ifdef SLAB_SUPPORTS_SYSFS
 		sysfs_slab_unlink(s);
 		sysfs_slab_release(s);
 #else
 		slab_kmem_cache_release(s);
 #endif
 	}

 	return 0;
 }

 void slab_kmem_cache_release(struct kmem_cache *s)
 {
 	__kmem_cache_release(s);
 	kfree_const(s->name);
 	kmem_cache_free(kmem_cache, s);
 }

 void kmem_cache_destroy(struct kmem_cache *s)
 {
 	int err;

 	if (unlikely(!s))
 		return;

 	mutex_lock(&slab_mutex);

 	s->refcount--;
 	if (s->refcount)
 		goto out_unlock;

 	err = shutdown_cache(s);
 	if (err) {
 		pr_err("%s %s: Slab cache still has objects\n",
 		       __func__, s->name);
 		dump_stack();
 	}
 out_unlock:
 	mutex_unlock(&slab_mutex);
 }
 EXPORT_SYMBOL(kmem_cache_destroy);

 /**
  * kmem_cache_shrink - Shrink a cache.
  * @cachep: The cache to shrink.
  *
  * Releases as many slabs as possible for a cache.
  * To help debugging, a zero exit status indicates all slabs were released.
  *
  * Return: %0 if all slabs were released, non-zero otherwise
  */
 int kmem_cache_shrink(struct kmem_cache *cachep)
 {
 	int ret;


 	kasan_cache_shrink(cachep);
 	ret = __kmem_cache_shrink(cachep);

 	return ret;
 }
 EXPORT_SYMBOL(kmem_cache_shrink);

 bool slab_is_available(void)
 {
 	return slab_state >= UP;
 }

 #ifdef CONFIG_PRINTK
 /**
  * kmem_valid_obj - does the pointer reference a valid slab object?
  * @object: pointer to query.
  *
  * Return: %true if the pointer is to a not-yet-freed object from
  * kmalloc() or kmem_cache_alloc(), either %true or %false if the pointer
  * is to an already-freed object, and %false otherwise.
  */
 bool kmem_valid_obj(void *object)
 {
 	struct page *page;

 	/* Some arches consider ZERO_SIZE_PTR to be a valid address. */
 	if (object < (void *)PAGE_SIZE || !virt_addr_valid(object))
 		return false;
 	page = virt_to_head_page(object);
 	return PageSlab(page);
 }
 EXPORT_SYMBOL_GPL(kmem_valid_obj);

 /**
  * kmem_dump_obj - Print available slab provenance information
  * @object: slab object for which to find provenance information.
  *
  * This function uses pr_cont(), so that the caller is expected to have
  * printed out whatever preamble is appropriate.  The provenance information
  * depends on the type of object and on how much debugging is enabled.
  * For a slab-cache object, the fact that it is a slab object is printed,
  * and, if available, the slab name, return address, and stack trace from
  * the allocation and last free path of that object.
  *
  * This function will splat if passed a pointer to a non-slab object.
  * If you are not sure what type of object you have, you should instead
  * use mem_dump_obj().
  */
 void kmem_dump_obj(void *object)
 {
 	char *cp = IS_ENABLED(CONFIG_MMU) ? "" : "/vmalloc";
 	int i;
 	struct page *page;
 	unsigned long ptroffset;
 	struct kmem_obj_info kp = { };

 	if (WARN_ON_ONCE(!virt_addr_valid(object)))
 		return;
 	page = virt_to_head_page(object);
 	if (WARN_ON_ONCE(!PageSlab(page))) {
 		pr_cont(" non-slab memory.\n");
 		return;
 	}
 	kmem_obj_info(&kp, object, page);
 	if (kp.kp_slab_cache)
 		pr_cont(" slab%s %s", cp, kp.kp_slab_cache->name);
 	else
 		pr_cont(" slab%s", cp);
 	if (kp.kp_objp)
 		pr_cont(" start %px", kp.kp_objp);
 	if (kp.kp_data_offset)
 		pr_cont(" data offset %lu", kp.kp_data_offset);
 	if (kp.kp_objp) {
 		ptroffset = ((char *)object - (char *)kp.kp_objp) - kp.kp_data_offset;
 		pr_cont(" pointer offset %lu", ptroffset);
 	}
 	if (kp.kp_slab_cache && kp.kp_slab_cache->usersize)
 		pr_cont(" size %u", kp.kp_slab_cache->usersize);
 	if (kp.kp_ret)
 		pr_cont(" allocated at %pS\n", kp.kp_ret);
 	else
 		pr_cont("\n");
 	for (i = 0; i < ARRAY_SIZE(kp.kp_stack); i++) {
 		if (!kp.kp_stack[i])
 			break;
 		pr_info("    %pS\n", kp.kp_stack[i]);
 	}

 	if (kp.kp_free_stack[0])
 		pr_cont(" Free path:\n");

 	for (i = 0; i < ARRAY_SIZE(kp.kp_free_stack); i++) {
 		if (!kp.kp_free_stack[i])
 			break;
 		pr_info("    %pS\n", kp.kp_free_stack[i]);
 	}

 }
 EXPORT_SYMBOL_GPL(kmem_dump_obj);
 #endif

 #ifndef CONFIG_SLOB
 /* Create a cache during boot when no slab services are available yet */
 void __init create_boot_cache(struct kmem_cache *s, const char *name,
 		unsigned int size, slab_flags_t flags,
 		unsigned int useroffset, unsigned int usersize)
 {
 	int err;
 	unsigned int align = ARCH_KMALLOC_MINALIGN;

 	s->name = name;
 	s->size = s->object_size = size;

 	/*
 	 * For power of two sizes, guarantee natural alignment for kmalloc
 	 * caches, regardless of SL*B debugging options.
 	 */
 	if (is_power_of_2(size))
 		align = max(align, size);
 	s->align = calculate_alignment(flags, align, size);

 	s->useroffset = useroffset;
 	s->usersize = usersize;

 	err = __kmem_cache_create(s, flags);

 	if (err)
 		panic("Creation of kmalloc slab %s size=%u failed. Reason %d\n",
 					name, size, err);

 	s->refcount = -1;	/* Exempt from merging for now */
 }

 struct kmem_cache *__init create_kmalloc_cache(const char *name,
 		unsigned int size, slab_flags_t flags,
 		unsigned int useroffset, unsigned int usersize)
 {
 	struct kmem_cache *s = kmem_cache_zalloc(kmem_cache, GFP_NOWAIT);

 	if (!s)
 		panic("Out of memory when creating slab %s\n", name);

 	create_boot_cache(s, name, size, flags, useroffset, usersize);
 	kasan_cache_create_kmalloc(s);
 	list_add(&s->list, &slab_caches);
 	s->refcount = 1;
 	return s;
 }

 struct kmem_cache *
 kmalloc_caches[NR_KMALLOC_TYPES][KMALLOC_SHIFT_HIGH + 1] __ro_after_init =
 { /* initialization for https://bugs.llvm.org/show_bug.cgi?id=42570 */ };
 EXPORT_SYMBOL(kmalloc_caches);

 /*
  * Conversion table for small slabs sizes / 8 to the index in the
  * kmalloc array. This is necessary for slabs < 192 since we have non power
  * of two cache sizes there. The size of larger slabs can be determined using
  * fls.
  */
 static u8 size_index[24] __ro_after_init = {
 	3,	/* 8 */
 	4,	/* 16 */
 	5,	/* 24 */
 	5,	/* 32 */
 	6,	/* 40 */
 	6,	/* 48 */
 	6,	/* 56 */
 	6,	/* 64 */
 	1,	/* 72 */
 	1,	/* 80 */
 	1,	/* 88 */
 	1,	/* 96 */
 	7,	/* 104 */
 	7,	/* 112 */
 	7,	/* 120 */
 	7,	/* 128 */
 	2,	/* 136 */
 	2,	/* 144 */
 	2,	/* 152 */
 	2,	/* 160 */
 	2,	/* 168 */
 	2,	/* 176 */
 	2,	/* 184 */
 	2	/* 192 */
 };

 static inline unsigned int size_index_elem(unsigned int bytes)
 {
 	return (bytes - 1) / 8;
 }

 /*
  * Find the kmem_cache structure that serves a given size of
  * allocation
  */
 struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
 {
 	unsigned int index;

 	if (size <= 192) {
 		if (!size)
 			return ZERO_SIZE_PTR;

 		index = size_index[size_index_elem(size)];
 	} else {
 		if (WARN_ON_ONCE(size > KMALLOC_MAX_CACHE_SIZE))
 			return NULL;
 		index = fls(size - 1);
 	}

 	return kmalloc_caches[kmalloc_type(flags)][index];
 }

 #ifdef CONFIG_ZONE_DMA
 #define KMALLOC_DMA_NAME(sz)	.name[KMALLOC_DMA] = "dma-kmalloc-" #sz,
 #else
 #define KMALLOC_DMA_NAME(sz)
 #endif

 #ifdef CONFIG_MEMCG_KMEM
 #define KMALLOC_CGROUP_NAME(sz)	.name[KMALLOC_CGROUP] = "kmalloc-cg-" #sz,
 #else
 #define KMALLOC_CGROUP_NAME(sz)
 #endif

 #define INIT_KMALLOC_INFO(__size, __short_size)			\
 {								\
 	.name[KMALLOC_NORMAL]  = "kmalloc-" #__short_size,	\
 	.name[KMALLOC_RECLAIM] = "kmalloc-rcl-" #__short_size,	\
 	KMALLOC_CGROUP_NAME(__short_size)			\
 	KMALLOC_DMA_NAME(__short_size)				\
 	.size = __size,						\
 }

 /*
  * kmalloc_info[] is to make slub_debug=,kmalloc-xx option work at boot time.
  * kmalloc_index() supports up to 2^25=32MB, so the final entry of the table is
  * kmalloc-32M.
  */
 const struct kmalloc_info_struct kmalloc_info[] __initconst = {
 	INIT_KMALLOC_INFO(0, 0),
 	INIT_KMALLOC_INFO(96, 96),
 	INIT_KMALLOC_INFO(192, 192),
 	INIT_KMALLOC_INFO(8, 8),
 	INIT_KMALLOC_INFO(16, 16),
 	INIT_KMALLOC_INFO(32, 32),
 	INIT_KMALLOC_INFO(64, 64),
 	INIT_KMALLOC_INFO(128, 128),
 	INIT_KMALLOC_INFO(256, 256),
 	INIT_KMALLOC_INFO(512, 512),
 	INIT_KMALLOC_INFO(1024, 1k),
 	INIT_KMALLOC_INFO(2048, 2k),
 	INIT_KMALLOC_INFO(4096, 4k),
 	INIT_KMALLOC_INFO(8192, 8k),
 	INIT_KMALLOC_INFO(16384, 16k),
 	INIT_KMALLOC_INFO(32768, 32k),
 	INIT_KMALLOC_INFO(65536, 64k),
 	INIT_KMALLOC_INFO(131072, 128k),
 	INIT_KMALLOC_INFO(262144, 256k),
 	INIT_KMALLOC_INFO(524288, 512k),
 	INIT_KMALLOC_INFO(1048576, 1M),
 	INIT_KMALLOC_INFO(2097152, 2M),
 	INIT_KMALLOC_INFO(4194304, 4M),
 	INIT_KMALLOC_INFO(8388608, 8M),
 	INIT_KMALLOC_INFO(16777216, 16M),
 	INIT_KMALLOC_INFO(33554432, 32M)
 };

 /*
  * Patch up the size_index table if we have strange large alignment
  * requirements for the kmalloc array. This is only the case for
  * MIPS it seems. The standard arches will not generate any code here.
  *
  * Largest permitted alignment is 256 bytes due to the way we
  * handle the index determination for the smaller caches.
  *
  * Make sure that nothing crazy happens if someone starts tinkering
  * around with ARCH_KMALLOC_MINALIGN
  */
 void __init setup_kmalloc_cache_index_table(void)
 {
 	unsigned int i;

 	BUILD_BUG_ON(KMALLOC_MIN_SIZE > 256 ||
 		(KMALLOC_MIN_SIZE & (KMALLOC_MIN_SIZE - 1)));

 	for (i = 8; i < KMALLOC_MIN_SIZE; i += 8) {
 		unsigned int elem = size_index_elem(i);

 		if (elem >= ARRAY_SIZE(size_index))
 			break;
 		size_index[elem] = KMALLOC_SHIFT_LOW;
 	}

 	if (KMALLOC_MIN_SIZE >= 64) {
 		/*
 		 * The 96 byte size cache is not used if the alignment
 		 * is 64 byte.
 		 */
 		for (i = 64 + 8; i <= 96; i += 8)
 			size_index[size_index_elem(i)] = 7;

 	}

 	if (KMALLOC_MIN_SIZE >= 128) {
 		/*
 		 * The 192 byte sized cache is not used if the alignment
 		 * is 128 byte. Redirect kmalloc to use the 256 byte cache
 		 * instead.
 		 */
 		for (i = 128 + 8; i <= 192; i += 8)
 			size_index[size_index_elem(i)] = 8;
 	}
 }

 static void __init
 new_kmalloc_cache(int idx, enum kmalloc_cache_type type, slab_flags_t flags)
 {
 	if (type == KMALLOC_RECLAIM) {
 		flags |= SLAB_RECLAIM_ACCOUNT;
 	} else if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_CGROUP)) {
 		if (cgroup_memory_nokmem) {
 			kmalloc_caches[type][idx] = kmalloc_caches[KMALLOC_NORMAL][idx];
 			return;
 		}
 		flags |= SLAB_ACCOUNT;
 	}

 	kmalloc_caches[type][idx] = create_kmalloc_cache(
 					kmalloc_info[idx].name[type],
 					kmalloc_info[idx].size, flags, 0,
 					kmalloc_info[idx].size);

 	/*
 	 * If CONFIG_MEMCG_KMEM is enabled, disable cache merging for
 	 * KMALLOC_NORMAL caches.
 	 */
 	if (IS_ENABLED(CONFIG_MEMCG_KMEM) && (type == KMALLOC_NORMAL))
 		kmalloc_caches[type][idx]->refcount = -1;
 }

 /*
  * Create the kmalloc array. Some of the regular kmalloc arrays
  * may already have been created because they were needed to
  * enable allocations for slab creation.
  */
 void __init create_kmalloc_caches(slab_flags_t flags)
 {
 	int i;
 	enum kmalloc_cache_type type;

 	/*
 	 * Including KMALLOC_CGROUP if CONFIG_MEMCG_KMEM defined
 	 */
 	for (type = KMALLOC_NORMAL; type <= KMALLOC_RECLAIM; type++) {
 		for (i = KMALLOC_SHIFT_LOW; i <= KMALLOC_SHIFT_HIGH; i++) {
 			if (!kmalloc_caches[type][i])
 				new_kmalloc_cache(i, type, flags);

 			/*
 			 * Caches that are not of the two-to-the-power-of size.
 			 * These have to be created immediately after the
 			 * earlier power of two caches
 			 */
 			if (KMALLOC_MIN_SIZE <= 32 && i == 6 &&
 					!kmalloc_caches[type][1])
 				new_kmalloc_cache(1, type, flags);
 			if (KMALLOC_MIN_SIZE <= 64 && i == 7 &&
 					!kmalloc_caches[type][2])
 				new_kmalloc_cache(2, type, flags);
 		}
 	}

 	/* Kmalloc array is now usable */
 	slab_state = UP;

 #ifdef CONFIG_ZONE_DMA
 	for (i = 0; i <= KMALLOC_SHIFT_HIGH; i++) {
 		struct kmem_cache *s = kmalloc_caches[KMALLOC_NORMAL][i];

 		if (s) {
 			kmalloc_caches[KMALLOC_DMA][i] = create_kmalloc_cache(
 				kmalloc_info[i].name[KMALLOC_DMA],
 				kmalloc_info[i].size,
 				SLAB_CACHE_DMA | flags, 0,
 				kmalloc_info[i].size);
 		}
 	}
 #endif
 }
 #endif /* !CONFIG_SLOB */

 gfp_t kmalloc_fix_flags(gfp_t flags)
 {
 	gfp_t invalid_mask = flags & GFP_SLAB_BUG_MASK;

 	flags &= ~GFP_SLAB_BUG_MASK;
 	pr_warn("Unexpected gfp: %#x (%pGg). Fixing up to gfp: %#x (%pGg). Fix your code!\n",
 			invalid_mask, &invalid_mask, flags, &flags);
 	dump_stack();

 	return flags;
 }

 /*
  * To avoid unnecessary overhead, we pass through large allocation requests
  * directly to the page allocator. We use __GFP_COMP, because we will need to
  * know the allocation order to free the pages properly in kfree.
  */
 void *kmalloc_order(size_t size, gfp_t flags, unsigned int order)
 {
 	void *ret = NULL;
 	struct page *page;

 	if (unlikely(flags & GFP_SLAB_BUG_MASK))
 		flags = kmalloc_fix_flags(flags);

 	flags |= __GFP_COMP;
 	page = alloc_pages(flags, order);
 	if (likely(page)) {
 		ret = page_address(page);
 		mod_lruvec_page_state(page, NR_SLAB_UNRECLAIMABLE_B,
 				      PAGE_SIZE << order);
 	}
 	ret = kasan_kmalloc_large(ret, size, flags);
 	/* As ret might get tagged, call kmemleak hook after KASAN. */
 	kmemleak_alloc(ret, size, 1, flags);
 	return ret;
 }
 EXPORT_SYMBOL(kmalloc_order);

 #ifdef CONFIG_TRACING
 void *kmalloc_order_trace(size_t size, gfp_t flags, unsigned int order)
 {
 	void *ret = kmalloc_order(size, flags, order);
 	trace_kmalloc(_RET_IP_, ret, size, PAGE_SIZE << order, flags);
 	return ret;
 }
 EXPORT_SYMBOL(kmalloc_order_trace);
 #endif

 #ifdef CONFIG_SLAB_FREELIST_RANDOM
 /* Randomize a generic freelist */
 static void freelist_randomize(struct rnd_state *state, unsigned int *list,
 			       unsigned int count)
 {
 	unsigned int rand;
 	unsigned int i;

 	for (i = 0; i < count; i++)
 		list[i] = i;

 	/* Fisher-Yates shuffle */
 	for (i = count - 1; i > 0; i--) {
 		rand = prandom_u32_state(state);
 		rand %= (i + 1);
 		swap(list[i], list[rand]);
 	}
 }

 /* Create a random sequence per cache */
 int cache_random_seq_create(struct kmem_cache *cachep, unsigned int count,
 				    gfp_t gfp)
 {
 	struct rnd_state state;

 	if (count < 2 || cachep->random_seq)
 		return 0;

 	cachep->random_seq = kcalloc(count, sizeof(unsigned int), gfp);
 	if (!cachep->random_seq)
 		return -ENOMEM;

 	/* Get best entropy at this stage of boot */
 	prandom_seed_state(&state, get_random_long());

 	freelist_randomize(&state, cachep->random_seq, count);
 	return 0;
 }

 /* Destroy the per-cache random freelist sequence */
 void cache_random_seq_destroy(struct kmem_cache *cachep)
 {
 	kfree(cachep->random_seq);
 	cachep->random_seq = NULL;
 }
 #endif /* CONFIG_SLAB_FREELIST_RANDOM */

 #if defined(CONFIG_SLAB) || defined(CONFIG_SLUB_DEBUG)
 #ifdef CONFIG_SLAB
 #define SLABINFO_RIGHTS (0600)
 #else
 #define SLABINFO_RIGHTS (0400)
 #endif

 static void print_slabinfo_header(struct seq_file *m)
 {
 	/*
 	 * Output format version, so at least we can change it
 	 * without _too_ many complaints.
 	 */
 #ifdef CONFIG_DEBUG_SLAB
 	seq_puts(m, "slabinfo - version: 2.1 (statistics)\n");
 #else
 	seq_puts(m, "slabinfo - version: 2.1\n");
 #endif
 	seq_puts(m, "# name            <active_objs> <num_objs> <objsize> <objperslab> <pagesperslab>");
 	seq_puts(m, " : tunables <limit> <batchcount> <sharedfactor>");
 	seq_puts(m, " : slabdata <active_slabs> <num_slabs> <sharedavail>");
 #ifdef CONFIG_DEBUG_SLAB
 	seq_puts(m, " : globalstat <listallocs> <maxobjs> <grown> <reaped> <error> <maxfreeable> <nodeallocs> <remotefrees> <alienoverflow>");
 	seq_puts(m, " : cpustat <allochit> <allocmiss> <freehit> <freemiss>");
 #endif
 	seq_putc(m, '\n');
 }

 void *slab_start(struct seq_file *m, loff_t *pos)
 {
 	mutex_lock(&slab_mutex);
 	return seq_list_start(&slab_caches, *pos);
 }

 void *slab_next(struct seq_file *m, void *p, loff_t *pos)
 {
 	return seq_list_next(p, &slab_caches, pos);
 }

 void slab_stop(struct seq_file *m, void *p)
 {
 	mutex_unlock(&slab_mutex);
 }

 static void cache_show(struct kmem_cache *s, struct seq_file *m)
 {
 	struct slabinfo sinfo;

 	memset(&sinfo, 0, sizeof(sinfo));
 	get_slabinfo(s, &sinfo);

 	seq_printf(m, "%-17s %6lu %6lu %6u %4u %4d",
 		   s->name, sinfo.active_objs, sinfo.num_objs, s->size,
 		   sinfo.objects_per_slab, (1 << sinfo.cache_order));

 	seq_printf(m, " : tunables %4u %4u %4u",
 		   sinfo.limit, sinfo.batchcount, sinfo.shared);
 	seq_printf(m, " : slabdata %6lu %6lu %6lu",
 		   sinfo.active_slabs, sinfo.num_slabs, sinfo.shared_avail);
 	slabinfo_show_stats(m, s);
 	seq_putc(m, '\n');
 }

 static int slab_show(struct seq_file *m, void *p)
 {
 	struct kmem_cache *s = list_entry(p, struct kmem_cache, list);

 	if (p == slab_caches.next)
 		print_slabinfo_header(m);
 	cache_show(s, m);
 	return 0;
 }

 void dump_unreclaimable_slab(void)
 {
 	struct kmem_cache *s;
 	struct slabinfo sinfo;

 	/*
 	 * Here acquiring slab_mutex is risky since we don't prefer to get
 	 * sleep in oom path. But, without mutex hold, it may introduce a
 	 * risk of crash.
 	 * Use mutex_trylock to protect the list traverse, dump nothing
 	 * without acquiring the mutex.
 	 */
 	if (!mutex_trylock(&slab_mutex)) {
 		pr_warn("excessive unreclaimable slab but cannot dump stats\n");
 		return;
 	}

 	pr_info("Unreclaimable slab info:\n");
 	pr_info("Name                      Used          Total\n");

 	list_for_each_entry(s, &slab_caches, list) {
 		if (s->flags & SLAB_RECLAIM_ACCOUNT)
 			continue;

 		get_slabinfo(s, &sinfo);

 		if (sinfo.num_objs > 0)
 			pr_info("%-17s %10luKB %10luKB\n", s->name,
 				(sinfo.active_objs * s->size) / 1024,
 				(sinfo.num_objs * s->size) / 1024);
 	}
 	mutex_unlock(&slab_mutex);
 }

 #if defined(CONFIG_MEMCG_KMEM)
 int memcg_slab_show(struct seq_file *m, void *p)
 {
 	/*
 	 * Deprecated.
 	 * Please, take a look at tools/cgroup/slabinfo.py .
 	 */
 	return 0;
 }
 #endif

 /*
  * slabinfo_op - iterator that generates /proc/slabinfo
  *
  * Output layout:
  * cache-name
  * num-active-objs
  * total-objs
  * object size
  * num-active-slabs
  * total-slabs
  * num-pages-per-slab
  * + further values on SMP and with statistics enabled
  */
 static const struct seq_operations slabinfo_op = {
 	.start = slab_start,
 	.next = slab_next,
 	.stop = slab_stop,
 	.show = slab_show,
 };

 static int slabinfo_open(struct inode *inode, struct file *file)
 {
 	return seq_open(file, &slabinfo_op);
 }

 static const struct proc_ops slabinfo_proc_ops = {
 	.proc_flags	= PROC_ENTRY_PERMANENT,
 	.proc_open	= slabinfo_open,
 	.proc_read	= seq_read,
 	.proc_write	= slabinfo_write,
 	.proc_lseek	= seq_lseek,
 	.proc_release	= seq_release,
 };

 static int __init slab_proc_init(void)
 {
 	proc_create("slabinfo", SLABINFO_RIGHTS, NULL, &slabinfo_proc_ops);
 	return 0;
 }
 module_init(slab_proc_init);

 #endif /* CONFIG_SLAB || CONFIG_SLUB_DEBUG */

 static __always_inline void *__do_krealloc(const void *p, size_t new_size,
 					   gfp_t flags)
 {
 	void *ret;
 	size_t ks;

 	/* Don't use instrumented ksize to allow precise KASAN poisoning. */
 	if (likely(!ZERO_OR_NULL_PTR(p))) {
 		if (!kasan_check_byte(p))
 			return NULL;
 		ks = kfence_ksize(p) ?: __ksize(p);
 	} else
 		ks = 0;

 	/* If the object still fits, repoison it precisely. */
 	if (ks >= new_size) {
 		p = kasan_krealloc((void *)p, new_size, flags);
 		return (void *)p;
 	}

 	ret = kmalloc_track_caller(new_size, flags);
 	if (ret && p) {
 		/* Disable KASAN checks as the object's redzone is accessed. */
 		kasan_disable_current();
 		memcpy(ret, kasan_reset_tag(p), ks);
 		kasan_enable_current();
 	}

 	return ret;
 }

 /**
  * krealloc - reallocate memory. The contents will remain unchanged.
  * @p: object to reallocate memory for.
  * @new_size: how many bytes of memory are required.
  * @flags: the type of memory to allocate.
  *
  * The contents of the object pointed to are preserved up to the
  * lesser of the new and old sizes (__GFP_ZERO flag is effectively ignored).
  * If @p is %NULL, krealloc() behaves exactly like kmalloc().  If @new_size
  * is 0 and @p is not a %NULL pointer, the object pointed to is freed.
  *
  * Return: pointer to the allocated memory or %NULL in case of error
  */
 void *krealloc(const void *p, size_t new_size, gfp_t flags)
 {
 	void *ret;

 	if (unlikely(!new_size)) {
 		kfree(p);
 		return ZERO_SIZE_PTR;
 	}

 	ret = __do_krealloc(p, new_size, flags);
 	if (ret && kasan_reset_tag(p) != kasan_reset_tag(ret))
 		kfree(p);

 	return ret;
 }
 EXPORT_SYMBOL(krealloc);

 /**
  * kfree_sensitive - Clear sensitive information in memory before freeing
  * @p: object to free memory of
  *
  * The memory of the object @p points to is zeroed before freed.
  * If @p is %NULL, kfree_sensitive() does nothing.
  *
  * Note: this function zeroes the whole allocated buffer which can be a good
  * deal bigger than the requested buffer size passed to kmalloc(). So be
  * careful when using this function in performance sensitive code.
  */
 void kfree_sensitive(const void *p)
 {
 	size_t ks;
 	void *mem = (void *)p;

 	ks = ksize(mem);
 	if (ks)
 		memzero_explicit(mem, ks);
 	kfree(mem);
 }
 EXPORT_SYMBOL(kfree_sensitive);

 /**
  * ksize - get the actual amount of memory allocated for a given object
  * @objp: Pointer to the object
  *
  * kmalloc may internally round up allocations and return more memory
  * than requested. ksize() can be used to determine the actual amount of
  * memory allocated. The caller may use this additional memory, even though
  * a smaller amount of memory was initially specified with the kmalloc call.
  * The caller must guarantee that objp points to a valid object previously
  * allocated with either kmalloc() or kmem_cache_alloc(). The object
  * must not be freed during the duration of the call.
  *
  * Return: size of the actual memory used by @objp in bytes
  */
 size_t ksize(const void *objp)
 {
 	size_t size;

 	/*
 	 * We need to first check that the pointer to the object is valid, and
 	 * only then unpoison the memory. The report printed from ksize() is
 	 * more useful, then when it's printed later when the behaviour could
 	 * be undefined due to a potential use-after-free or double-free.
 	 *
 	 * We use kasan_check_byte(), which is supported for the hardware
 	 * tag-based KASAN mode, unlike kasan_check_read/write().
 	 *
 	 * If the pointed to memory is invalid, we return 0 to avoid users of
 	 * ksize() writing to and potentially corrupting the memory region.
 	 *
 	 * We want to perform the check before __ksize(), to avoid potentially
 	 * crashing in __ksize() due to accessing invalid metadata.
 	 */
 	if (unlikely(ZERO_OR_NULL_PTR(objp)) || !kasan_check_byte(objp))
 		return 0;

 	size = kfence_ksize(objp) ?: __ksize(objp);
 	/*
 	 * We assume that ksize callers could use whole allocated area,
 	 * so we need to unpoison this area.
 	 */
 	kasan_unpoison_range(objp, size);
 	return size;
 }
 EXPORT_SYMBOL(ksize);

 /* Tracepoints definitions. */
 EXPORT_TRACEPOINT_SYMBOL(kmalloc);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc);
 EXPORT_TRACEPOINT_SYMBOL(kmalloc_node);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc_node);
 EXPORT_TRACEPOINT_SYMBOL(kfree);
 EXPORT_TRACEPOINT_SYMBOL(kmem_cache_free);

 int should_failslab(struct kmem_cache *s, gfp_t gfpflags)
 {
 	if (__should_failslab(s, gfpflags))
 		return -ENOMEM;
 	return 0;
 }
 ALLOW_ERROR_INJECTION(should_failslab, ERRNO);