drm: fix race between driver loading and userspace open.

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / mm / percpu.c

/*
 * mm/percpu.c - percpu memory allocator
 *
 * Copyright (C) 2009           SUSE Linux Products GmbH
 * Copyright (C) 2009           Tejun Heo <tj@kernel.org>
 *
 * This file is released under the GPLv2.
 *
 * This is percpu allocator which can handle both static and dynamic
 * areas.  Percpu areas are allocated in chunks.  Each chunk is
 * consisted of boot-time determined number of units and the first
 * chunk is used for static percpu variables in the kernel image
 * (special boot time alloc/init handling necessary as these areas
 * need to be brought up before allocation services are running).
 * Unit grows as necessary and all units grow or shrink in unison.
 * When a chunk is filled up, another chunk is allocated.
 *
 *  c0                           c1                         c2
 *  -------------------          -------------------        ------------
 * | u0 | u1 | u2 | u3 |        | u0 | u1 | u2 | u3 |      | u0 | u1 | u
 *  -------------------  ......  -------------------  ....  ------------
 *
 * Allocation is done in offset-size areas of single unit space.  Ie,
 * an area of 512 bytes at 6k in c1 occupies 512 bytes at 6k of c1:u0,
 * c1:u1, c1:u2 and c1:u3.  On UMA, units corresponds directly to
 * cpus.  On NUMA, the mapping can be non-linear and even sparse.
 * Percpu access can be done by configuring percpu base registers
 * according to cpu to unit mapping and pcpu_unit_size.
 *
 * There are usually many small percpu allocations many of them being
 * as small as 4 bytes.  The allocator organizes chunks into lists
 * according to free size and tries to allocate from the fullest one.
 * Each chunk keeps the maximum contiguous area size hint which is
 * guaranteed to be eqaul to or larger than the maximum contiguous
 * area in the chunk.  This helps the allocator not to iterate the
 * chunk maps unnecessarily.
 *
 * Allocation state in each chunk is kept using an array of integers
 * on chunk->map.  A positive value in the map represents a free
 * region and negative allocated.  Allocation inside a chunk is done
 * by scanning this map sequentially and serving the first matching
 * entry.  This is mostly copied from the percpu_modalloc() allocator.
 * Chunks can be determined from the address using the index field
 * in the page struct. The index field contains a pointer to the chunk.
 *
 * To use this allocator, arch code should do the followings.
 *
 * - define __addr_to_pcpu_ptr() and __pcpu_ptr_to_addr() to translate
 *   regular address to percpu pointer and back if they need to be
 *   different from the default
 *
 * - use pcpu_setup_first_chunk() during percpu area initialization to
 *   setup the first chunk containing the kernel static percpu area
 */

#include <linux/bitmap.h>
#include <linux/bootmem.h>
#include <linux/err.h>
#include <linux/list.h>
#include <linux/log2.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/mutex.h>
#include <linux/percpu.h>
#include <linux/pfn.h>
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/vmalloc.h>
#include <linux/workqueue.h>

#include <asm/cacheflush.h>
#include <asm/sections.h>
#include <asm/tlbflush.h>
#include <asm/io.h>

#define PCPU_SLOT_BASE_SHIFT            5       /* 1-31 shares the same slot */
#define PCPU_DFL_MAP_ALLOC              16      /* start a map with 16 ents */

/* default addr <-> pcpu_ptr mapping, override in asm/percpu.h if necessary */
#ifndef __addr_to_pcpu_ptr
#define __addr_to_pcpu_ptr(addr)                                        \
        (void __percpu *)((unsigned long)(addr) -                       \
                          (unsigned long)pcpu_base_addr +               \
                          (unsigned long)__per_cpu_start)
#endif
#ifndef __pcpu_ptr_to_addr
#define __pcpu_ptr_to_addr(ptr)                                         \
        (void __force *)((unsigned long)(ptr) +                         \
                         (unsigned long)pcpu_base_addr -                \
                         (unsigned long)__per_cpu_start)
#endif

struct pcpu_chunk {
        struct list_head        list;           /* linked to pcpu_slot lists */
        int                     free_size;      /* free bytes in the chunk */
        int                     contig_hint;    /* max contiguous size hint */
        void                    *base_addr;     /* base address of this chunk */
        int                     map_used;       /* # of map entries used */
        int                     map_alloc;      /* # of map entries allocated */
        int                     *map;           /* allocation map */
        void                    *data;          /* chunk data */
        bool                    immutable;      /* no [de]population allowed */
        unsigned long           populated[];    /* populated bitmap */
};

static int pcpu_unit_pages __read_mostly;
static int pcpu_unit_size __read_mostly;
static int pcpu_nr_units __read_mostly;
static int pcpu_atom_size __read_mostly;
static int pcpu_nr_slots __read_mostly;
static size_t pcpu_chunk_struct_size __read_mostly;

/* cpus with the lowest and highest unit numbers */
static unsigned int pcpu_first_unit_cpu __read_mostly;
static unsigned int pcpu_last_unit_cpu __read_mostly;

/* the address of the first chunk which starts with the kernel static area */
void *pcpu_base_addr __read_mostly;
EXPORT_SYMBOL_GPL(pcpu_base_addr);

static const int *pcpu_unit_map __read_mostly;          /* cpu -> unit */
const unsigned long *pcpu_unit_offsets __read_mostly;   /* cpu -> unit offset */

/* group information, used for vm allocation */
static int pcpu_nr_groups __read_mostly;
static const unsigned long *pcpu_group_offsets __read_mostly;
static const size_t *pcpu_group_sizes __read_mostly;

/*
 * The first chunk which always exists.  Note that unlike other
 * chunks, this one can be allocated and mapped in several different
 * ways and thus often doesn't live in the vmalloc area.
 */
static struct pcpu_chunk *pcpu_first_chunk;

/*
 * Optional reserved chunk.  This chunk reserves part of the first
 * chunk and serves it for reserved allocations.  The amount of
 * reserved offset is in pcpu_reserved_chunk_limit.  When reserved
 * area doesn't exist, the following variables contain NULL and 0
 * respectively.
 */
static struct pcpu_chunk *pcpu_reserved_chunk;
static int pcpu_reserved_chunk_limit;

/*
 * Synchronization rules.
 *
 * There are two locks - pcpu_alloc_mutex and pcpu_lock.  The former
 * protects allocation/reclaim paths, chunks, populated bitmap and
 * vmalloc mapping.  The latter is a spinlock and protects the index
 * data structures - chunk slots, chunks and area maps in chunks.
 *
 * During allocation, pcpu_alloc_mutex is kept locked all the time and
 * pcpu_lock is grabbed and released as necessary.  All actual memory
 * allocations are done using GFP_KERNEL with pcpu_lock released.  In
 * general, percpu memory can't be allocated with irq off but
 * irqsave/restore are still used in alloc path so that it can be used
 * from early init path - sched_init() specifically.
 *
 * Free path accesses and alters only the index data structures, so it
 * can be safely called from atomic context.  When memory needs to be
 * returned to the system, free path schedules reclaim_work which
 * grabs both pcpu_alloc_mutex and pcpu_lock, unlinks chunks to be
 * reclaimed, release both locks and frees the chunks.  Note that it's
 * necessary to grab both locks to remove a chunk from circulation as
 * allocation path might be referencing the chunk with only
 * pcpu_alloc_mutex locked.
 */
static DEFINE_MUTEX(pcpu_alloc_mutex);  /* protects whole alloc and reclaim */
static DEFINE_SPINLOCK(pcpu_lock);      /* protects index data structures */

static struct list_head *pcpu_slot __read_mostly; /* chunk list slots */

/* reclaim work to release fully free chunks, scheduled from free path */
static void pcpu_reclaim(struct work_struct *work);
static DECLARE_WORK(pcpu_reclaim_work, pcpu_reclaim);

static bool pcpu_addr_in_first_chunk(void *addr)
{
        void *first_start = pcpu_first_chunk->base_addr;

        return addr >= first_start && addr < first_start + pcpu_unit_size;
}

static bool pcpu_addr_in_reserved_chunk(void *addr)
{
        void *first_start = pcpu_first_chunk->base_addr;

        return addr >= first_start &&
                addr < first_start + pcpu_reserved_chunk_limit;
}

static int __pcpu_size_to_slot(int size)
{
        int highbit = fls(size);        /* size is in bytes */
        return max(highbit - PCPU_SLOT_BASE_SHIFT + 2, 1);
}

static int pcpu_size_to_slot(int size)
{
        if (size == pcpu_unit_size)
                return pcpu_nr_slots - 1;
        return __pcpu_size_to_slot(size);
}

static int pcpu_chunk_slot(const struct pcpu_chunk *chunk)
{
        if (chunk->free_size < sizeof(int) || chunk->contig_hint < sizeof(int))
                return 0;

        return pcpu_size_to_slot(chunk->free_size);
}

/* set the pointer to a chunk in a page struct */
static void pcpu_set_page_chunk(struct page *page, struct pcpu_chunk *pcpu)
{
        page->index = (unsigned long)pcpu;
}

/* obtain pointer to a chunk from a page struct */
static struct pcpu_chunk *pcpu_get_page_chunk(struct page *page)
{
        return (struct pcpu_chunk *)page->index;
}

static int __maybe_unused pcpu_page_idx(unsigned int cpu, int page_idx)
{
        return pcpu_unit_map[cpu] * pcpu_unit_pages + page_idx;
}

static unsigned long pcpu_chunk_addr(struct pcpu_chunk *chunk,
                                     unsigned int cpu, int page_idx)
{
        return (unsigned long)chunk->base_addr + pcpu_unit_offsets[cpu] +
                (page_idx << PAGE_SHIFT);
}

static void __maybe_unused pcpu_next_unpop(struct pcpu_chunk *chunk,
                                           int *rs, int *re, int end)
{
        *rs = find_next_zero_bit(chunk->populated, end, *rs);
        *re = find_next_bit(chunk->populated, end, *rs + 1);
}

static void __maybe_unused pcpu_next_pop(struct pcpu_chunk *chunk,
                                         int *rs, int *re, int end)
{
        *rs = find_next_bit(chunk->populated, end, *rs);
        *re = find_next_zero_bit(chunk->populated, end, *rs + 1);
}

/*
 * (Un)populated page region iterators.  Iterate over (un)populated
 * page regions betwen @start and @end in @chunk.  @rs and @re should
 * be integer variables and will be set to start and end page index of
 * the current region.
 */
#define pcpu_for_each_unpop_region(chunk, rs, re, start, end)               \
        for ((rs) = (start), pcpu_next_unpop((chunk), &(rs), &(re), (end)); \
             (rs) < (re);                                                   \
             (rs) = (re) + 1, pcpu_next_unpop((chunk), &(rs), &(re), (end)))

#define pcpu_for_each_pop_region(chunk, rs, re, start, end)                 \
        for ((rs) = (start), pcpu_next_pop((chunk), &(rs), &(re), (end));   \
             (rs) < (re);                                                   \
             (rs) = (re) + 1, pcpu_next_pop((chunk), &(rs), &(re), (end)))

/**
 * pcpu_mem_alloc - allocate memory
 * @size: bytes to allocate
 *
 * Allocate @size bytes.  If @size is smaller than PAGE_SIZE,
 * kzalloc() is used; otherwise, vmalloc() is used.  The returned
 * memory is always zeroed.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.
 *
 * RETURNS:
 * Pointer to the allocated area on success, NULL on failure.
 */
static void *pcpu_mem_alloc(size_t size)
{
        if (WARN_ON_ONCE(!slab_is_available()))
                return NULL;

        if (size <= PAGE_SIZE)
                return kzalloc(size, GFP_KERNEL);
        else {
                void *ptr = vmalloc(size);
                if (ptr)
                        memset(ptr, 0, size);
                return ptr;
        }
}

/**
 * pcpu_mem_free - free memory
 * @ptr: memory to free
 * @size: size of the area
 *
 * Free @ptr.  @ptr should have been allocated using pcpu_mem_alloc().
 */
static void pcpu_mem_free(void *ptr, size_t size)
{
        if (size <= PAGE_SIZE)
                kfree(ptr);
        else
                vfree(ptr);
}

/**
 * pcpu_chunk_relocate - put chunk in the appropriate chunk slot
 * @chunk: chunk of interest
 * @oslot: the previous slot it was on
 *
 * This function is called after an allocation or free changed @chunk.
 * New slot according to the changed state is determined and @chunk is
 * moved to the slot.  Note that the reserved chunk is never put on
 * chunk slots.
 *
 * CONTEXT:
 * pcpu_lock.
 */
static void pcpu_chunk_relocate(struct pcpu_chunk *chunk, int oslot)
{
        int nslot = pcpu_chunk_slot(chunk);

        if (chunk != pcpu_reserved_chunk && oslot != nslot) {
                if (oslot < nslot)
                        list_move(&chunk->list, &pcpu_slot[nslot]);
                else
                        list_move_tail(&chunk->list, &pcpu_slot[nslot]);
        }
}

/**
 * pcpu_need_to_extend - determine whether chunk area map needs to be extended
 * @chunk: chunk of interest
 *
 * Determine whether area map of @chunk needs to be extended to
 * accomodate a new allocation.
 *
 * CONTEXT:
 * pcpu_lock.
 *
 * RETURNS:
 * New target map allocation length if extension is necessary, 0
 * otherwise.
 */
static int pcpu_need_to_extend(struct pcpu_chunk *chunk)
{
        int new_alloc;

        if (chunk->map_alloc >= chunk->map_used + 2)
                return 0;

        new_alloc = PCPU_DFL_MAP_ALLOC;
        while (new_alloc < chunk->map_used + 2)
                new_alloc *= 2;

        return new_alloc;
}

/**
 * pcpu_extend_area_map - extend area map of a chunk
 * @chunk: chunk of interest
 * @new_alloc: new target allocation length of the area map
 *
 * Extend area map of @chunk to have @new_alloc entries.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.  Grabs and releases pcpu_lock.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
static int pcpu_extend_area_map(struct pcpu_chunk *chunk, int new_alloc)
{
        int *old = NULL, *new = NULL;
        size_t old_size = 0, new_size = new_alloc * sizeof(new[0]);
        unsigned long flags;

        new = pcpu_mem_alloc(new_size);
        if (!new)
                return -ENOMEM;

        /* acquire pcpu_lock and switch to new area map */
        spin_lock_irqsave(&pcpu_lock, flags);

        if (new_alloc <= chunk->map_alloc)
                goto out_unlock;

        old_size = chunk->map_alloc * sizeof(chunk->map[0]);
        old = chunk->map;

        memcpy(new, old, old_size);

        chunk->map_alloc = new_alloc;
        chunk->map = new;
        new = NULL;

out_unlock:
        spin_unlock_irqrestore(&pcpu_lock, flags);

        /*
         * pcpu_mem_free() might end up calling vfree() which uses
         * IRQ-unsafe lock and thus can't be called under pcpu_lock.
         */
        pcpu_mem_free(old, old_size);
        pcpu_mem_free(new, new_size);

        return 0;
}

/**
 * pcpu_split_block - split a map block
 * @chunk: chunk of interest
 * @i: index of map block to split
 * @head: head size in bytes (can be 0)
 * @tail: tail size in bytes (can be 0)
 *
 * Split the @i'th map block into two or three blocks.  If @head is
 * non-zero, @head bytes block is inserted before block @i moving it
 * to @i+1 and reducing its size by @head bytes.
 *
 * If @tail is non-zero, the target block, which can be @i or @i+1
 * depending on @head, is reduced by @tail bytes and @tail byte block
 * is inserted after the target block.
 *
 * @chunk->map must have enough free slots to accomodate the split.
 *
 * CONTEXT:
 * pcpu_lock.
 */
static void pcpu_split_block(struct pcpu_chunk *chunk, int i,
                             int head, int tail)
{
        int nr_extra = !!head + !!tail;

        BUG_ON(chunk->map_alloc < chunk->map_used + nr_extra);

        /* insert new subblocks */
        memmove(&chunk->map[i + nr_extra], &chunk->map[i],
                sizeof(chunk->map[0]) * (chunk->map_used - i));
        chunk->map_used += nr_extra;

        if (head) {
                chunk->map[i + 1] = chunk->map[i] - head;
                chunk->map[i++] = head;
        }
        if (tail) {
                chunk->map[i++] -= tail;
                chunk->map[i] = tail;
        }
}

/**
 * pcpu_alloc_area - allocate area from a pcpu_chunk
 * @chunk: chunk of interest
 * @size: wanted size in bytes
 * @align: wanted align
 *
 * Try to allocate @size bytes area aligned at @align from @chunk.
 * Note that this function only allocates the offset.  It doesn't
 * populate or map the area.
 *
 * @chunk->map must have at least two free slots.
 *
 * CONTEXT:
 * pcpu_lock.
 *
 * RETURNS:
 * Allocated offset in @chunk on success, -1 if no matching area is
 * found.
 */
static int pcpu_alloc_area(struct pcpu_chunk *chunk, int size, int align)
{
        int oslot = pcpu_chunk_slot(chunk);
        int max_contig = 0;
        int i, off;

        for (i = 0, off = 0; i < chunk->map_used; off += abs(chunk->map[i++])) {
                bool is_last = i + 1 == chunk->map_used;
                int head, tail;

                /* extra for alignment requirement */
                head = ALIGN(off, align) - off;
                BUG_ON(i == 0 && head != 0);

                if (chunk->map[i] < 0)
                        continue;
                if (chunk->map[i] < head + size) {
                        max_contig = max(chunk->map[i], max_contig);
                        continue;
                }

                /*
                 * If head is small or the previous block is free,
                 * merge'em.  Note that 'small' is defined as smaller
                 * than sizeof(int), which is very small but isn't too
                 * uncommon for percpu allocations.
                 */
                if (head && (head < sizeof(int) || chunk->map[i - 1] > 0)) {
                        if (chunk->map[i - 1] > 0)
                                chunk->map[i - 1] += head;
                        else {
                                chunk->map[i - 1] -= head;
                                chunk->free_size -= head;
                        }
                        chunk->map[i] -= head;
                        off += head;
                        head = 0;
                }

                /* if tail is small, just keep it around */
                tail = chunk->map[i] - head - size;
                if (tail < sizeof(int))
                        tail = 0;

                /* split if warranted */
                if (head || tail) {
                        pcpu_split_block(chunk, i, head, tail);
                        if (head) {
                                i++;
                                off += head;
                                max_contig = max(chunk->map[i - 1], max_contig);
                        }
                        if (tail)
                                max_contig = max(chunk->map[i + 1], max_contig);
                }

                /* update hint and mark allocated */
                if (is_last)
                        chunk->contig_hint = max_contig; /* fully scanned */
                else
                        chunk->contig_hint = max(chunk->contig_hint,
                                                 max_contig);

                chunk->free_size -= chunk->map[i];
                chunk->map[i] = -chunk->map[i];

                pcpu_chunk_relocate(chunk, oslot);
                return off;
        }

        chunk->contig_hint = max_contig;        /* fully scanned */
        pcpu_chunk_relocate(chunk, oslot);

        /* tell the upper layer that this chunk has no matching area */
        return -1;
}

/**
 * pcpu_free_area - free area to a pcpu_chunk
 * @chunk: chunk of interest
 * @freeme: offset of area to free
 *
 * Free area starting from @freeme to @chunk.  Note that this function
 * only modifies the allocation map.  It doesn't depopulate or unmap
 * the area.
 *
 * CONTEXT:
 * pcpu_lock.
 */
static void pcpu_free_area(struct pcpu_chunk *chunk, int freeme)
{
        int oslot = pcpu_chunk_slot(chunk);
        int i, off;

        for (i = 0, off = 0; i < chunk->map_used; off += abs(chunk->map[i++]))
                if (off == freeme)
                        break;
        BUG_ON(off != freeme);
        BUG_ON(chunk->map[i] > 0);

        chunk->map[i] = -chunk->map[i];
        chunk->free_size += chunk->map[i];

        /* merge with previous? */
        if (i > 0 && chunk->map[i - 1] >= 0) {
                chunk->map[i - 1] += chunk->map[i];
                chunk->map_used--;
                memmove(&chunk->map[i], &chunk->map[i + 1],
                        (chunk->map_used - i) * sizeof(chunk->map[0]));
                i--;
        }
        /* merge with next? */
        if (i + 1 < chunk->map_used && chunk->map[i + 1] >= 0) {
                chunk->map[i] += chunk->map[i + 1];
                chunk->map_used--;
                memmove(&chunk->map[i + 1], &chunk->map[i + 2],
                        (chunk->map_used - (i + 1)) * sizeof(chunk->map[0]));
        }

        chunk->contig_hint = max(chunk->map[i], chunk->contig_hint);
        pcpu_chunk_relocate(chunk, oslot);
}

static struct pcpu_chunk *pcpu_alloc_chunk(void)
{
        struct pcpu_chunk *chunk;

        chunk = pcpu_mem_alloc(pcpu_chunk_struct_size);
        if (!chunk)
                return NULL;

        chunk->map = pcpu_mem_alloc(PCPU_DFL_MAP_ALLOC * sizeof(chunk->map[0]));
        if (!chunk->map) {
                kfree(chunk);
                return NULL;
        }

        chunk->map_alloc = PCPU_DFL_MAP_ALLOC;
        chunk->map[chunk->map_used++] = pcpu_unit_size;

        INIT_LIST_HEAD(&chunk->list);
        chunk->free_size = pcpu_unit_size;
        chunk->contig_hint = pcpu_unit_size;

        return chunk;
}

static void pcpu_free_chunk(struct pcpu_chunk *chunk)
{
        if (!chunk)
                return;
        pcpu_mem_free(chunk->map, chunk->map_alloc * sizeof(chunk->map[0]));
        kfree(chunk);
}

/*
 * Chunk management implementation.
 *
 * To allow different implementations, chunk alloc/free and
 * [de]population are implemented in a separate file which is pulled
 * into this file and compiled together.  The following functions
 * should be implemented.
 *
 * pcpu_populate_chunk          - populate the specified range of a chunk
 * pcpu_depopulate_chunk        - depopulate the specified range of a chunk
 * pcpu_create_chunk            - create a new chunk
 * pcpu_destroy_chunk           - destroy a chunk, always preceded by full depop
 * pcpu_addr_to_page            - translate address to physical address
 * pcpu_verify_alloc_info       - check alloc_info is acceptable during init
 */
static int pcpu_populate_chunk(struct pcpu_chunk *chunk, int off, int size);
static void pcpu_depopulate_chunk(struct pcpu_chunk *chunk, int off, int size);
static struct pcpu_chunk *pcpu_create_chunk(void);
static void pcpu_destroy_chunk(struct pcpu_chunk *chunk);
static struct page *pcpu_addr_to_page(void *addr);
static int __init pcpu_verify_alloc_info(const struct pcpu_alloc_info *ai);

#ifdef CONFIG_NEED_PER_CPU_KM
#include "percpu-km.c"
#else
#include "percpu-vm.c"
#endif

/**
 * pcpu_chunk_addr_search - determine chunk containing specified address
 * @addr: address for which the chunk needs to be determined.
 *
 * RETURNS:
 * The address of the found chunk.
 */
static struct pcpu_chunk *pcpu_chunk_addr_search(void *addr)
{
        /* is it in the first chunk? */
        if (pcpu_addr_in_first_chunk(addr)) {
                /* is it in the reserved area? */
                if (pcpu_addr_in_reserved_chunk(addr))
                        return pcpu_reserved_chunk;
                return pcpu_first_chunk;
        }

        /*
         * The address is relative to unit0 which might be unused and
         * thus unmapped.  Offset the address to the unit space of the
         * current processor before looking it up in the vmalloc
         * space.  Note that any possible cpu id can be used here, so
         * there's no need to worry about preemption or cpu hotplug.
         */
        addr += pcpu_unit_offsets[raw_smp_processor_id()];
        return pcpu_get_page_chunk(pcpu_addr_to_page(addr));
}

/**
 * pcpu_alloc - the percpu allocator
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 * @reserved: allocate from the reserved chunk if available
 *
 * Allocate percpu area of @size bytes aligned at @align.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.
 *
 * RETURNS:
 * Percpu pointer to the allocated area on success, NULL on failure.
 */
static void __percpu *pcpu_alloc(size_t size, size_t align, bool reserved)
{
        static int warn_limit = 10;
        struct pcpu_chunk *chunk;
        const char *err;
        int slot, off, new_alloc;
        unsigned long flags;

        if (unlikely(!size || size > PCPU_MIN_UNIT_SIZE || align > PAGE_SIZE)) {
                WARN(true, "illegal size (%zu) or align (%zu) for "
                     "percpu allocation\n", size, align);
                return NULL;
        }

        mutex_lock(&pcpu_alloc_mutex);
        spin_lock_irqsave(&pcpu_lock, flags);

        /* serve reserved allocations from the reserved chunk if available */
        if (reserved && pcpu_reserved_chunk) {
                chunk = pcpu_reserved_chunk;

                if (size > chunk->contig_hint) {
                        err = "alloc from reserved chunk failed";
                        goto fail_unlock;
                }

                while ((new_alloc = pcpu_need_to_extend(chunk))) {
                        spin_unlock_irqrestore(&pcpu_lock, flags);
                        if (pcpu_extend_area_map(chunk, new_alloc) < 0) {
                                err = "failed to extend area map of reserved chunk";
                                goto fail_unlock_mutex;
                        }
                        spin_lock_irqsave(&pcpu_lock, flags);
                }

                off = pcpu_alloc_area(chunk, size, align);
                if (off >= 0)
                        goto area_found;

                err = "alloc from reserved chunk failed";
                goto fail_unlock;
        }

restart:
        /* search through normal chunks */
        for (slot = pcpu_size_to_slot(size); slot < pcpu_nr_slots; slot++) {
                list_for_each_entry(chunk, &pcpu_slot[slot], list) {
                        if (size > chunk->contig_hint)
                                continue;

                        new_alloc = pcpu_need_to_extend(chunk);
                        if (new_alloc) {
                                spin_unlock_irqrestore(&pcpu_lock, flags);
                                if (pcpu_extend_area_map(chunk,
                                                         new_alloc) < 0) {
                                        err = "failed to extend area map";
                                        goto fail_unlock_mutex;
                                }
                                spin_lock_irqsave(&pcpu_lock, flags);
                                /*
                                 * pcpu_lock has been dropped, need to
                                 * restart cpu_slot list walking.
                                 */
                                goto restart;
                        }

                        off = pcpu_alloc_area(chunk, size, align);
                        if (off >= 0)
                                goto area_found;
                }
        }

        /* hmmm... no space left, create a new chunk */
        spin_unlock_irqrestore(&pcpu_lock, flags);

        chunk = pcpu_create_chunk();
        if (!chunk) {
                err = "failed to allocate new chunk";
                goto fail_unlock_mutex;
        }

        spin_lock_irqsave(&pcpu_lock, flags);
        pcpu_chunk_relocate(chunk, -1);
        goto restart;

area_found:
        spin_unlock_irqrestore(&pcpu_lock, flags);

        /* populate, map and clear the area */
        if (pcpu_populate_chunk(chunk, off, size)) {
                spin_lock_irqsave(&pcpu_lock, flags);
                pcpu_free_area(chunk, off);
                err = "failed to populate";
                goto fail_unlock;
        }

        mutex_unlock(&pcpu_alloc_mutex);

        /* return address relative to base address */
        return __addr_to_pcpu_ptr(chunk->base_addr + off);

fail_unlock:
        spin_unlock_irqrestore(&pcpu_lock, flags);
fail_unlock_mutex:
        mutex_unlock(&pcpu_alloc_mutex);
        if (warn_limit) {
                pr_warning("PERCPU: allocation failed, size=%zu align=%zu, "
                           "%s\n", size, align, err);
                dump_stack();
                if (!--warn_limit)
                        pr_info("PERCPU: limit reached, disable warning\n");
        }
        return NULL;
}

/**
 * __alloc_percpu - allocate dynamic percpu area
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 *
 * Allocate percpu area of @size bytes aligned at @align.  Might
 * sleep.  Might trigger writeouts.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.
 *
 * RETURNS:
 * Percpu pointer to the allocated area on success, NULL on failure.
 */
void __percpu *__alloc_percpu(size_t size, size_t align)
{
        return pcpu_alloc(size, align, false);
}
EXPORT_SYMBOL_GPL(__alloc_percpu);

/**
 * __alloc_reserved_percpu - allocate reserved percpu area
 * @size: size of area to allocate in bytes
 * @align: alignment of area (max PAGE_SIZE)
 *
 * Allocate percpu area of @size bytes aligned at @align from reserved
 * percpu area if arch has set it up; otherwise, allocation is served
 * from the same dynamic area.  Might sleep.  Might trigger writeouts.
 *
 * CONTEXT:
 * Does GFP_KERNEL allocation.
 *
 * RETURNS:
 * Percpu pointer to the allocated area on success, NULL on failure.
 */
void __percpu *__alloc_reserved_percpu(size_t size, size_t align)
{
        return pcpu_alloc(size, align, true);
}

/**
 * pcpu_reclaim - reclaim fully free chunks, workqueue function
 * @work: unused
 *
 * Reclaim all fully free chunks except for the first one.
 *
 * CONTEXT:
 * workqueue context.
 */
static void pcpu_reclaim(struct work_struct *work)
{
        LIST_HEAD(todo);
        struct list_head *head = &pcpu_slot[pcpu_nr_slots - 1];
        struct pcpu_chunk *chunk, *next;

        mutex_lock(&pcpu_alloc_mutex);
        spin_lock_irq(&pcpu_lock);

        list_for_each_entry_safe(chunk, next, head, list) {
                WARN_ON(chunk->immutable);

                /* spare the first one */
                if (chunk == list_first_entry(head, struct pcpu_chunk, list))
                        continue;

                list_move(&chunk->list, &todo);
        }

        spin_unlock_irq(&pcpu_lock);

        list_for_each_entry_safe(chunk, next, &todo, list) {
                pcpu_depopulate_chunk(chunk, 0, pcpu_unit_size);
                pcpu_destroy_chunk(chunk);
        }

        mutex_unlock(&pcpu_alloc_mutex);
}

/**
 * free_percpu - free percpu area
 * @ptr: pointer to area to free
 *
 * Free percpu area @ptr.
 *
 * CONTEXT:
 * Can be called from atomic context.
 */
void free_percpu(void __percpu *ptr)
{
        void *addr;
        struct pcpu_chunk *chunk;
        unsigned long flags;
        int off;

        if (!ptr)
                return;

        addr = __pcpu_ptr_to_addr(ptr);

        spin_lock_irqsave(&pcpu_lock, flags);

        chunk = pcpu_chunk_addr_search(addr);
        off = addr - chunk->base_addr;

        pcpu_free_area(chunk, off);

        /* if there are more than one fully free chunks, wake up grim reaper */
        if (chunk->free_size == pcpu_unit_size) {
                struct pcpu_chunk *pos;

                list_for_each_entry(pos, &pcpu_slot[pcpu_nr_slots - 1], list)
                        if (pos != chunk) {
                                schedule_work(&pcpu_reclaim_work);
                                break;
                        }
        }

        spin_unlock_irqrestore(&pcpu_lock, flags);
}
EXPORT_SYMBOL_GPL(free_percpu);

/**
 * is_kernel_percpu_address - test whether address is from static percpu area
 * @addr: address to test
 *
 * Test whether @addr belongs to in-kernel static percpu area.  Module
 * static percpu areas are not considered.  For those, use
 * is_module_percpu_address().
 *
 * RETURNS:
 * %true if @addr is from in-kernel static percpu area, %false otherwise.
 */
bool is_kernel_percpu_address(unsigned long addr)
{
        const size_t static_size = __per_cpu_end - __per_cpu_start;
        void __percpu *base = __addr_to_pcpu_ptr(pcpu_base_addr);
        unsigned int cpu;

        for_each_possible_cpu(cpu) {
                void *start = per_cpu_ptr(base, cpu);

                if ((void *)addr >= start && (void *)addr < start + static_size)
                        return true;
        }
        return false;
}

/**
 * per_cpu_ptr_to_phys - convert translated percpu address to physical address
 * @addr: the address to be converted to physical address
 *
 * Given @addr which is dereferenceable address obtained via one of
 * percpu access macros, this function translates it into its physical
 * address.  The caller is responsible for ensuring @addr stays valid
 * until this function finishes.
 *
 * RETURNS:
 * The physical address for @addr.
 */
phys_addr_t per_cpu_ptr_to_phys(void *addr)
{
        void __percpu *base = __addr_to_pcpu_ptr(pcpu_base_addr);
        bool in_first_chunk = false;
        unsigned long first_start, first_end;
        unsigned int cpu;

        /*
         * The following test on first_start/end isn't strictly
         * necessary but will speed up lookups of addresses which
         * aren't in the first chunk.
         */
        first_start = pcpu_chunk_addr(pcpu_first_chunk, pcpu_first_unit_cpu, 0);
        first_end = pcpu_chunk_addr(pcpu_first_chunk, pcpu_last_unit_cpu,
                                    pcpu_unit_pages);
        if ((unsigned long)addr >= first_start &&
            (unsigned long)addr < first_end) {
                for_each_possible_cpu(cpu) {
                        void *start = per_cpu_ptr(base, cpu);

                        if (addr >= start && addr < start + pcpu_unit_size) {
                                in_first_chunk = true;
                                break;
                        }
                }
        }

        if (in_first_chunk) {
                if ((unsigned long)addr < VMALLOC_START ||
                    (unsigned long)addr >= VMALLOC_END)
                        return __pa(addr);
                else
                        return page_to_phys(vmalloc_to_page(addr));
        } else
                return page_to_phys(pcpu_addr_to_page(addr));
}

/**
 * pcpu_alloc_alloc_info - allocate percpu allocation info
 * @nr_groups: the number of groups
 * @nr_units: the number of units
 *
 * Allocate ai which is large enough for @nr_groups groups containing
 * @nr_units units.  The returned ai's groups[0].cpu_map points to the
 * cpu_map array which is long enough for @nr_units and filled with
 * NR_CPUS.  It's the caller's responsibility to initialize cpu_map
 * pointer of other groups.
 *
 * RETURNS:
 * Pointer to the allocated pcpu_alloc_info on success, NULL on
 * failure.
 */
struct pcpu_alloc_info * __init pcpu_alloc_alloc_info(int nr_groups,
                                                      int nr_units)
{
        struct pcpu_alloc_info *ai;
        size_t base_size, ai_size;
        void *ptr;
        int unit;

        base_size = ALIGN(sizeof(*ai) + nr_groups * sizeof(ai->groups[0]),
                          __alignof__(ai->groups[0].cpu_map[0]));
        ai_size = base_size + nr_units * sizeof(ai->groups[0].cpu_map[0]);

        ptr = alloc_bootmem_nopanic(PFN_ALIGN(ai_size));
        if (!ptr)
                return NULL;
        ai = ptr;
        ptr += base_size;

        ai->groups[0].cpu_map = ptr;

        for (unit = 0; unit < nr_units; unit++)
                ai->groups[0].cpu_map[unit] = NR_CPUS;

        ai->nr_groups = nr_groups;
        ai->__ai_size = PFN_ALIGN(ai_size);

        return ai;
}

/**
 * pcpu_free_alloc_info - free percpu allocation info
 * @ai: pcpu_alloc_info to free
 *
 * Free @ai which was allocated by pcpu_alloc_alloc_info().
 */
void __init pcpu_free_alloc_info(struct pcpu_alloc_info *ai)
{
        free_bootmem(__pa(ai), ai->__ai_size);
}

/**
 * pcpu_build_alloc_info - build alloc_info considering distances between CPUs
 * @reserved_size: the size of reserved percpu area in bytes
 * @dyn_size: minimum free size for dynamic allocation in bytes
 * @atom_size: allocation atom size
 * @cpu_distance_fn: callback to determine distance between cpus, optional
 *
 * This function determines grouping of units, their mappings to cpus
 * and other parameters considering needed percpu size, allocation
 * atom size and distances between CPUs.
 *
 * Groups are always mutliples of atom size and CPUs which are of
 * LOCAL_DISTANCE both ways are grouped together and share space for
 * units in the same group.  The returned configuration is guaranteed
 * to have CPUs on different nodes on different groups and >=75% usage
 * of allocated virtual address space.
 *
 * RETURNS:
 * On success, pointer to the new allocation_info is returned.  On
 * failure, ERR_PTR value is returned.
 */
static struct pcpu_alloc_info * __init pcpu_build_alloc_info(
                                size_t reserved_size, size_t dyn_size,
                                size_t atom_size,
                                pcpu_fc_cpu_distance_fn_t cpu_distance_fn)
{
        static int group_map[NR_CPUS] __initdata;
        static int group_cnt[NR_CPUS] __initdata;
        const size_t static_size = __per_cpu_end - __per_cpu_start;
        int nr_groups = 1, nr_units = 0;
        size_t size_sum, min_unit_size, alloc_size;
        int upa, max_upa, uninitialized_var(best_upa);  /* units_per_alloc */
        int last_allocs, group, unit;
        unsigned int cpu, tcpu;
        struct pcpu_alloc_info *ai;
        unsigned int *cpu_map;

        /* this function may be called multiple times */
        memset(group_map, 0, sizeof(group_map));
        memset(group_cnt, 0, sizeof(group_cnt));

        /* calculate size_sum and ensure dyn_size is enough for early alloc */
        size_sum = PFN_ALIGN(static_size + reserved_size +
                            max_t(size_t, dyn_size, PERCPU_DYNAMIC_EARLY_SIZE));
        dyn_size = size_sum - static_size - reserved_size;

        /*
         * Determine min_unit_size, alloc_size and max_upa such that
         * alloc_size is multiple of atom_size and is the smallest
         * which can accomodate 4k aligned segments which are equal to
         * or larger than min_unit_size.
         */
        min_unit_size = max_t(size_t, size_sum, PCPU_MIN_UNIT_SIZE);

        alloc_size = roundup(min_unit_size, atom_size);
        upa = alloc_size / min_unit_size;
        while (alloc_size % upa || ((alloc_size / upa) & ~PAGE_MASK))
                upa--;
        max_upa = upa;

        /* group cpus according to their proximity */
        for_each_possible_cpu(cpu) {
                group = 0;
        next_group:
                for_each_possible_cpu(tcpu) {
                        if (cpu == tcpu)
                                break;
                        if (group_map[tcpu] == group && cpu_distance_fn &&
                            (cpu_distance_fn(cpu, tcpu) > LOCAL_DISTANCE ||
                             cpu_distance_fn(tcpu, cpu) > LOCAL_DISTANCE)) {
                                group++;
                                nr_groups = max(nr_groups, group + 1);
                                goto next_group;
                        }
                }
                group_map[cpu] = group;
                group_cnt[group]++;
        }

        /*
         * Expand unit size until address space usage goes over 75%
         * and then as much as possible without using more address
         * space.
         */
        last_allocs = INT_MAX;
        for (upa = max_upa; upa; upa--) {
                int allocs = 0, wasted = 0;

                if (alloc_size % upa || ((alloc_size / upa) & ~PAGE_MASK))
                        continue;

                for (group = 0; group < nr_groups; group++) {
                        int this_allocs = DIV_ROUND_UP(group_cnt[group], upa);
                        allocs += this_allocs;
                        wasted += this_allocs * upa - group_cnt[group];
                }

                /*
                 * Don't accept if wastage is over 1/3.  The
                 * greater-than comparison ensures upa==1 always
                 * passes the following check.
                 */
                if (wasted > num_possible_cpus() / 3)
                        continue;

                /* and then don't consume more memory */
                if (allocs > last_allocs)
                        break;
                last_allocs = allocs;
                best_upa = upa;
        }
        upa = best_upa;

        /* allocate and fill alloc_info */
        for (group = 0; group < nr_groups; group++)
                nr_units += roundup(group_cnt[group], upa);

        ai = pcpu_alloc_alloc_info(nr_groups, nr_units);
        if (!ai)
                return ERR_PTR(-ENOMEM);
        cpu_map = ai->groups[0].cpu_map;

        for (group = 0; group < nr_groups; group++) {
                ai->groups[group].cpu_map = cpu_map;
                cpu_map += roundup(group_cnt[group], upa);
        }

        ai->static_size = static_size;
        ai->reserved_size = reserved_size;
        ai->dyn_size = dyn_size;
        ai->unit_size = alloc_size / upa;
        ai->atom_size = atom_size;
        ai->alloc_size = alloc_size;

        for (group = 0, unit = 0; group_cnt[group]; group++) {
                struct pcpu_group_info *gi = &ai->groups[group];

                /*
                 * Initialize base_offset as if all groups are located
                 * back-to-back.  The caller should update this to
                 * reflect actual allocation.
                 */
                gi->base_offset = unit * ai->unit_size;

                for_each_possible_cpu(cpu)
                        if (group_map[cpu] == group)
                                gi->cpu_map[gi->nr_units++] = cpu;
                gi->nr_units = roundup(gi->nr_units, upa);
                unit += gi->nr_units;
        }
        BUG_ON(unit != nr_units);

        return ai;
}

/**
 * pcpu_dump_alloc_info - print out information about pcpu_alloc_info
 * @lvl: loglevel
 * @ai: allocation info to dump
 *
 * Print out information about @ai using loglevel @lvl.
 */
static void pcpu_dump_alloc_info(const char *lvl,
                                 const struct pcpu_alloc_info *ai)
{
        int group_width = 1, cpu_width = 1, width;
        char empty_str[] = "--------";
        int alloc = 0, alloc_end = 0;
        int group, v;
        int upa, apl;   /* units per alloc, allocs per line */

        v = ai->nr_groups;
        while (v /= 10)
                group_width++;

        v = num_possible_cpus();
        while (v /= 10)
                cpu_width++;
        empty_str[min_t(int, cpu_width, sizeof(empty_str) - 1)] = '\0';

        upa = ai->alloc_size / ai->unit_size;
        width = upa * (cpu_width + 1) + group_width + 3;
        apl = rounddown_pow_of_two(max(60 / width, 1));

        printk("%spcpu-alloc: s%zu r%zu d%zu u%zu alloc=%zu*%zu",
               lvl, ai->static_size, ai->reserved_size, ai->dyn_size,
               ai->unit_size, ai->alloc_size / ai->atom_size, ai->atom_size);

        for (group = 0; group < ai->nr_groups; group++) {
                const struct pcpu_group_info *gi = &ai->groups[group];
                int unit = 0, unit_end = 0;

                BUG_ON(gi->nr_units % upa);
                for (alloc_end += gi->nr_units / upa;
                     alloc < alloc_end; alloc++) {
                        if (!(alloc % apl)) {
                                printk("\n");
                                printk("%spcpu-alloc: ", lvl);
                        }
                        printk("[%0*d] ", group_width, group);

                        for (unit_end += upa; unit < unit_end; unit++)
                                if (gi->cpu_map[unit] != NR_CPUS)
                                        printk("%0*d ", cpu_width,
                                               gi->cpu_map[unit]);
                                else
                                        printk("%s ", empty_str);
                }
        }
        printk("\n");
}

/**
 * pcpu_setup_first_chunk - initialize the first percpu chunk
 * @ai: pcpu_alloc_info describing how to percpu area is shaped
 * @base_addr: mapped address
 *
 * Initialize the first percpu chunk which contains the kernel static
 * perpcu area.  This function is to be called from arch percpu area
 * setup path.
 *
 * @ai contains all information necessary to initialize the first
 * chunk and prime the dynamic percpu allocator.
 *
 * @ai->static_size is the size of static percpu area.
 *
 * @ai->reserved_size, if non-zero, specifies the amount of bytes to
 * reserve after the static area in the first chunk.  This reserves
 * the first chunk such that it's available only through reserved
 * percpu allocation.  This is primarily used to serve module percpu
 * static areas on architectures where the addressing model has
 * limited offset range for symbol relocations to guarantee module
 * percpu symbols fall inside the relocatable range.
 *
 * @ai->dyn_size determines the number of bytes available for dynamic
 * allocation in the first chunk.  The area between @ai->static_size +
 * @ai->reserved_size + @ai->dyn_size and @ai->unit_size is unused.
 *
 * @ai->unit_size specifies unit size and must be aligned to PAGE_SIZE
 * and equal to or larger than @ai->static_size + @ai->reserved_size +
 * @ai->dyn_size.
 *
 * @ai->atom_size is the allocation atom size and used as alignment
 * for vm areas.
 *
 * @ai->alloc_size is the allocation size and always multiple of
 * @ai->atom_size.  This is larger than @ai->atom_size if
 * @ai->unit_size is larger than @ai->atom_size.
 *
 * @ai->nr_groups and @ai->groups describe virtual memory layout of
 * percpu areas.  Units which should be colocated are put into the
 * same group.  Dynamic VM areas will be allocated according to these
 * groupings.  If @ai->nr_groups is zero, a single group containing
 * all units is assumed.
 *
 * The caller should have mapped the first chunk at @base_addr and
 * copied static data to each unit.
 *
 * If the first chunk ends up with both reserved and dynamic areas, it
 * is served by two chunks - one to serve the core static and reserved
 * areas and the other for the dynamic area.  They share the same vm
 * and page map but uses different area allocation map to stay away
 * from each other.  The latter chunk is circulated in the chunk slots
 * and available for dynamic allocation like any other chunks.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
                                  void *base_addr)
{
        static char cpus_buf[4096] __initdata;
        static int smap[PERCPU_DYNAMIC_EARLY_SLOTS] __initdata;
        static int dmap[PERCPU_DYNAMIC_EARLY_SLOTS] __initdata;
        size_t dyn_size = ai->dyn_size;
        size_t size_sum = ai->static_size + ai->reserved_size + dyn_size;
        struct pcpu_chunk *schunk, *dchunk = NULL;
        unsigned long *group_offsets;
        size_t *group_sizes;
        unsigned long *unit_off;
        unsigned int cpu;
        int *unit_map;
        int group, unit, i;

        cpumask_scnprintf(cpus_buf, sizeof(cpus_buf), cpu_possible_mask);

#define PCPU_SETUP_BUG_ON(cond) do {                                    \
        if (unlikely(cond)) {                                           \
                pr_emerg("PERCPU: failed to initialize, %s", #cond);    \
                pr_emerg("PERCPU: cpu_possible_mask=%s\n", cpus_buf);   \
                pcpu_dump_alloc_info(KERN_EMERG, ai);                   \
                BUG();                                                  \
        }                                                               \
} while (0)

        /* sanity checks */
        PCPU_SETUP_BUG_ON(ai->nr_groups <= 0);
        PCPU_SETUP_BUG_ON(!ai->static_size);
        PCPU_SETUP_BUG_ON(!base_addr);
        PCPU_SETUP_BUG_ON(ai->unit_size < size_sum);
        PCPU_SETUP_BUG_ON(ai->unit_size & ~PAGE_MASK);
        PCPU_SETUP_BUG_ON(ai->unit_size < PCPU_MIN_UNIT_SIZE);
        PCPU_SETUP_BUG_ON(ai->dyn_size < PERCPU_DYNAMIC_EARLY_SIZE);
        PCPU_SETUP_BUG_ON(pcpu_verify_alloc_info(ai) < 0);

        /* process group information and build config tables accordingly */
        group_offsets = alloc_bootmem(ai->nr_groups * sizeof(group_offsets[0]));
        group_sizes = alloc_bootmem(ai->nr_groups * sizeof(group_sizes[0]));
        unit_map = alloc_bootmem(nr_cpu_ids * sizeof(unit_map[0]));
        unit_off = alloc_bootmem(nr_cpu_ids * sizeof(unit_off[0]));

        for (cpu = 0; cpu < nr_cpu_ids; cpu++)
                unit_map[cpu] = UINT_MAX;
        pcpu_first_unit_cpu = NR_CPUS;

        for (group = 0, unit = 0; group < ai->nr_groups; group++, unit += i) {
                const struct pcpu_group_info *gi = &ai->groups[group];

                group_offsets[group] = gi->base_offset;
                group_sizes[group] = gi->nr_units * ai->unit_size;

                for (i = 0; i < gi->nr_units; i++) {
                        cpu = gi->cpu_map[i];
                        if (cpu == NR_CPUS)
                                continue;

                        PCPU_SETUP_BUG_ON(cpu > nr_cpu_ids);
                        PCPU_SETUP_BUG_ON(!cpu_possible(cpu));
                        PCPU_SETUP_BUG_ON(unit_map[cpu] != UINT_MAX);

                        unit_map[cpu] = unit + i;
                        unit_off[cpu] = gi->base_offset + i * ai->unit_size;

                        if (pcpu_first_unit_cpu == NR_CPUS)
                                pcpu_first_unit_cpu = cpu;
                }
        }
        pcpu_last_unit_cpu = cpu;
        pcpu_nr_units = unit;

        for_each_possible_cpu(cpu)
                PCPU_SETUP_BUG_ON(unit_map[cpu] == UINT_MAX);

        /* we're done parsing the input, undefine BUG macro and dump config */
#undef PCPU_SETUP_BUG_ON
        pcpu_dump_alloc_info(KERN_INFO, ai);

        pcpu_nr_groups = ai->nr_groups;
        pcpu_group_offsets = group_offsets;
        pcpu_group_sizes = group_sizes;
        pcpu_unit_map = unit_map;
        pcpu_unit_offsets = unit_off;

        /* determine basic parameters */
        pcpu_unit_pages = ai->unit_size >> PAGE_SHIFT;
        pcpu_unit_size = pcpu_unit_pages << PAGE_SHIFT;
        pcpu_atom_size = ai->atom_size;
        pcpu_chunk_struct_size = sizeof(struct pcpu_chunk) +
                BITS_TO_LONGS(pcpu_unit_pages) * sizeof(unsigned long);

        /*
         * Allocate chunk slots.  The additional last slot is for
         * empty chunks.
         */
        pcpu_nr_slots = __pcpu_size_to_slot(pcpu_unit_size) + 2;
        pcpu_slot = alloc_bootmem(pcpu_nr_slots * sizeof(pcpu_slot[0]));
        for (i = 0; i < pcpu_nr_slots; i++)
                INIT_LIST_HEAD(&pcpu_slot[i]);

        /*
         * Initialize static chunk.  If reserved_size is zero, the
         * static chunk covers static area + dynamic allocation area
         * in the first chunk.  If reserved_size is not zero, it
         * covers static area + reserved area (mostly used for module
         * static percpu allocation).
         */
        schunk = alloc_bootmem(pcpu_chunk_struct_size);
        INIT_LIST_HEAD(&schunk->list);
        schunk->base_addr = base_addr;
        schunk->map = smap;
        schunk->map_alloc = ARRAY_SIZE(smap);
        schunk->immutable = true;
        bitmap_fill(schunk->populated, pcpu_unit_pages);

        if (ai->reserved_size) {
                schunk->free_size = ai->reserved_size;
                pcpu_reserved_chunk = schunk;
                pcpu_reserved_chunk_limit = ai->static_size + ai->reserved_size;
        } else {
                schunk->free_size = dyn_size;
                dyn_size = 0;                   /* dynamic area covered */
        }
        schunk->contig_hint = schunk->free_size;

        schunk->map[schunk->map_used++] = -ai->static_size;
        if (schunk->free_size)
                schunk->map[schunk->map_used++] = schunk->free_size;

        /* init dynamic chunk if necessary */
        if (dyn_size) {
                dchunk = alloc_bootmem(pcpu_chunk_struct_size);
                INIT_LIST_HEAD(&dchunk->list);
                dchunk->base_addr = base_addr;
                dchunk->map = dmap;
                dchunk->map_alloc = ARRAY_SIZE(dmap);
                dchunk->immutable = true;
                bitmap_fill(dchunk->populated, pcpu_unit_pages);

                dchunk->contig_hint = dchunk->free_size = dyn_size;
                dchunk->map[dchunk->map_used++] = -pcpu_reserved_chunk_limit;
                dchunk->map[dchunk->map_used++] = dchunk->free_size;
        }

        /* link the first chunk in */
        pcpu_first_chunk = dchunk ?: schunk;
        pcpu_chunk_relocate(pcpu_first_chunk, -1);

        /* we're done */
        pcpu_base_addr = base_addr;
        return 0;
}

const char *pcpu_fc_names[PCPU_FC_NR] __initdata = {
        [PCPU_FC_AUTO]  = "auto",
        [PCPU_FC_EMBED] = "embed",
        [PCPU_FC_PAGE]  = "page",
};

enum pcpu_fc pcpu_chosen_fc __initdata = PCPU_FC_AUTO;

static int __init percpu_alloc_setup(char *str)
{
        if (0)
                /* nada */;
#ifdef CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK
        else if (!strcmp(str, "embed"))
                pcpu_chosen_fc = PCPU_FC_EMBED;
#endif
#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
        else if (!strcmp(str, "page"))
                pcpu_chosen_fc = PCPU_FC_PAGE;
#endif
        else
                pr_warning("PERCPU: unknown allocator %s specified\n", str);

        return 0;
}
early_param("percpu_alloc", percpu_alloc_setup);

#if defined(CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK) || \
        !defined(CONFIG_HAVE_SETUP_PER_CPU_AREA)
/**
 * pcpu_embed_first_chunk - embed the first percpu chunk into bootmem
 * @reserved_size: the size of reserved percpu area in bytes
 * @dyn_size: minimum free size for dynamic allocation in bytes
 * @atom_size: allocation atom size
 * @cpu_distance_fn: callback to determine distance between cpus, optional
 * @alloc_fn: function to allocate percpu page
 * @free_fn: funtion to free percpu page
 *
 * This is a helper to ease setting up embedded first percpu chunk and
 * can be called where pcpu_setup_first_chunk() is expected.
 *
 * If this function is used to setup the first chunk, it is allocated
 * by calling @alloc_fn and used as-is without being mapped into
 * vmalloc area.  Allocations are always whole multiples of @atom_size
 * aligned to @atom_size.
 *
 * This enables the first chunk to piggy back on the linear physical
 * mapping which often uses larger page size.  Please note that this
 * can result in very sparse cpu->unit mapping on NUMA machines thus
 * requiring large vmalloc address space.  Don't use this allocator if
 * vmalloc space is not orders of magnitude larger than distances
 * between node memory addresses (ie. 32bit NUMA machines).
 *
 * @dyn_size specifies the minimum dynamic area size.
 *
 * If the needed size is smaller than the minimum or specified unit
 * size, the leftover is returned using @free_fn.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size,
                                  size_t atom_size,
                                  pcpu_fc_cpu_distance_fn_t cpu_distance_fn,
                                  pcpu_fc_alloc_fn_t alloc_fn,
                                  pcpu_fc_free_fn_t free_fn)
{
        void *base = (void *)ULONG_MAX;
        void **areas = NULL;
        struct pcpu_alloc_info *ai;
        size_t size_sum, areas_size, max_distance;
        int group, i, rc;

        ai = pcpu_build_alloc_info(reserved_size, dyn_size, atom_size,
                                   cpu_distance_fn);
        if (IS_ERR(ai))
                return PTR_ERR(ai);

        size_sum = ai->static_size + ai->reserved_size + ai->dyn_size;
        areas_size = PFN_ALIGN(ai->nr_groups * sizeof(void *));

        areas = alloc_bootmem_nopanic(areas_size);
        if (!areas) {
                rc = -ENOMEM;
                goto out_free;
        }

        /* allocate, copy and determine base address */
        for (group = 0; group < ai->nr_groups; group++) {
                struct pcpu_group_info *gi = &ai->groups[group];
                unsigned int cpu = NR_CPUS;
                void *ptr;

                for (i = 0; i < gi->nr_units && cpu == NR_CPUS; i++)
                        cpu = gi->cpu_map[i];
                BUG_ON(cpu == NR_CPUS);

                /* allocate space for the whole group */
                ptr = alloc_fn(cpu, gi->nr_units * ai->unit_size, atom_size);
                if (!ptr) {
                        rc = -ENOMEM;
                        goto out_free_areas;
                }
                areas[group] = ptr;

                base = min(ptr, base);

                for (i = 0; i < gi->nr_units; i++, ptr += ai->unit_size) {
                        if (gi->cpu_map[i] == NR_CPUS) {
                                /* unused unit, free whole */
                                free_fn(ptr, ai->unit_size);
                                continue;
                        }
                        /* copy and return the unused part */
                        memcpy(ptr, __per_cpu_load, ai->static_size);
                        free_fn(ptr + size_sum, ai->unit_size - size_sum);
                }
        }

        /* base address is now known, determine group base offsets */
        max_distance = 0;
        for (group = 0; group < ai->nr_groups; group++) {
                ai->groups[group].base_offset = areas[group] - base;
                max_distance = max_t(size_t, max_distance,
                                     ai->groups[group].base_offset);
        }
        max_distance += ai->unit_size;

        /* warn if maximum distance is further than 75% of vmalloc space */
        if (max_distance > (VMALLOC_END - VMALLOC_START) * 3 / 4) {
                pr_warning("PERCPU: max_distance=0x%zx too large for vmalloc "
                           "space 0x%lx\n",
                           max_distance, VMALLOC_END - VMALLOC_START);
#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
                /* and fail if we have fallback */
                rc = -EINVAL;
                goto out_free;
#endif
        }

        pr_info("PERCPU: Embedded %zu pages/cpu @%p s%zu r%zu d%zu u%zu\n",
                PFN_DOWN(size_sum), base, ai->static_size, ai->reserved_size,
                ai->dyn_size, ai->unit_size);

        rc = pcpu_setup_first_chunk(ai, base);
        goto out_free;

out_free_areas:
        for (group = 0; group < ai->nr_groups; group++)
                free_fn(areas[group],
                        ai->groups[group].nr_units * ai->unit_size);
out_free:
        pcpu_free_alloc_info(ai);
        if (areas)
                free_bootmem(__pa(areas), areas_size);
        return rc;
}
#endif /* CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK ||
          !CONFIG_HAVE_SETUP_PER_CPU_AREA */

#ifdef CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK
/**
 * pcpu_page_first_chunk - map the first chunk using PAGE_SIZE pages
 * @reserved_size: the size of reserved percpu area in bytes
 * @alloc_fn: function to allocate percpu page, always called with PAGE_SIZE
 * @free_fn: funtion to free percpu page, always called with PAGE_SIZE
 * @populate_pte_fn: function to populate pte
 *
 * This is a helper to ease setting up page-remapped first percpu
 * chunk and can be called where pcpu_setup_first_chunk() is expected.
 *
 * This is the basic allocator.  Static percpu area is allocated
 * page-by-page into vmalloc area.
 *
 * RETURNS:
 * 0 on success, -errno on failure.
 */
int __init pcpu_page_first_chunk(size_t reserved_size,
                                 pcpu_fc_alloc_fn_t alloc_fn,
                                 pcpu_fc_free_fn_t free_fn,
                                 pcpu_fc_populate_pte_fn_t populate_pte_fn)
{
        static struct vm_struct vm;
        struct pcpu_alloc_info *ai;
        char psize_str[16];
        int unit_pages;
        size_t pages_size;
        struct page **pages;
        int unit, i, j, rc;

        snprintf(psize_str, sizeof(psize_str), "%luK", PAGE_SIZE >> 10);

        ai = pcpu_build_alloc_info(reserved_size, 0, PAGE_SIZE, NULL);
        if (IS_ERR(ai))
                return PTR_ERR(ai);
        BUG_ON(ai->nr_groups != 1);
        BUG_ON(ai->groups[0].nr_units != num_possible_cpus());

        unit_pages = ai->unit_size >> PAGE_SHIFT;

        /* unaligned allocations can't be freed, round up to page size */
        pages_size = PFN_ALIGN(unit_pages * num_possible_cpus() *
                               sizeof(pages[0]));
        pages = alloc_bootmem(pages_size);

        /* allocate pages */
        j = 0;
        for (unit = 0; unit < num_possible_cpus(); unit++)
                for (i = 0; i < unit_pages; i++) {
                        unsigned int cpu = ai->groups[0].cpu_map[unit];
                        void *ptr;

                        ptr = alloc_fn(cpu, PAGE_SIZE, PAGE_SIZE);
                        if (!ptr) {
                                pr_warning("PERCPU: failed to allocate %s page "
                                           "for cpu%u\n", psize_str, cpu);
                                goto enomem;
                        }
                        pages[j++] = virt_to_page(ptr);
                }

        /* allocate vm area, map the pages and copy static data */
        vm.flags = VM_ALLOC;
        vm.size = num_possible_cpus() * ai->unit_size;
        vm_area_register_early(&vm, PAGE_SIZE);

        for (unit = 0; unit < num_possible_cpus(); unit++) {
                unsigned long unit_addr =
                        (unsigned long)vm.addr + unit * ai->unit_size;

                for (i = 0; i < unit_pages; i++)
                        populate_pte_fn(unit_addr + (i << PAGE_SHIFT));

                /* pte already populated, the following shouldn't fail */
                rc = __pcpu_map_pages(unit_addr, &pages[unit * unit_pages],
                                      unit_pages);
                if (rc < 0)
                        panic("failed to map percpu area, err=%d\n", rc);

                /*
                 * FIXME: Archs with virtual cache should flush local
                 * cache for the linear mapping here - something
                 * equivalent to flush_cache_vmap() on the local cpu.
                 * flush_cache_vmap() can't be used as most supporting
                 * data structures are not set up yet.
                 */

                /* copy static data */
                memcpy((void *)unit_addr, __per_cpu_load, ai->static_size);
        }

        /* we're ready, commit */
        pr_info("PERCPU: %d %s pages/cpu @%p s%zu r%zu d%zu\n",
                unit_pages, psize_str, vm.addr, ai->static_size,
                ai->reserved_size, ai->dyn_size);

        rc = pcpu_setup_first_chunk(ai, vm.addr);
        goto out_free_ar;

enomem:
        while (--j >= 0)
                free_fn(page_address(pages[j]), PAGE_SIZE);
        rc = -ENOMEM;
out_free_ar:
        free_bootmem(__pa(pages), pages_size);
        pcpu_free_alloc_info(ai);
        return rc;
}
#endif /* CONFIG_NEED_PER_CPU_PAGE_FIRST_CHUNK */

/*
 * Generic percpu area setup.
 *
 * The embedding helper is used because its behavior closely resembles
 * the original non-dynamic generic percpu area setup.  This is
 * important because many archs have addressing restrictions and might
 * fail if the percpu area is located far away from the previous
 * location.  As an added bonus, in non-NUMA cases, embedding is
 * generally a good idea TLB-wise because percpu area can piggy back
 * on the physical linear memory mapping which uses large page
 * mappings on applicable archs.
 */
#ifndef CONFIG_HAVE_SETUP_PER_CPU_AREA
unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
EXPORT_SYMBOL(__per_cpu_offset);

static void * __init pcpu_dfl_fc_alloc(unsigned int cpu, size_t size,
                                       size_t align)
{
        return __alloc_bootmem_nopanic(size, align, __pa(MAX_DMA_ADDRESS));
}

static void __init pcpu_dfl_fc_free(void *ptr, size_t size)
{
        free_bootmem(__pa(ptr), size);
}

void __init setup_per_cpu_areas(void)
{
        unsigned long delta;
        unsigned int cpu;
        int rc;

        /*
         * Always reserve area for module percpu variables.  That's
         * what the legacy allocator did.
         */
        rc = pcpu_embed_first_chunk(PERCPU_MODULE_RESERVE,
                                    PERCPU_DYNAMIC_RESERVE, PAGE_SIZE, NULL,
                                    pcpu_dfl_fc_alloc, pcpu_dfl_fc_free);
        if (rc < 0)
                panic("Failed to initialized percpu areas.");

        delta = (unsigned long)pcpu_base_addr - (unsigned long)__per_cpu_start;
        for_each_possible_cpu(cpu)
                __per_cpu_offset[cpu] = delta + pcpu_unit_offsets[cpu];
}
#endif /* CONFIG_HAVE_SETUP_PER_CPU_AREA */

/*
 * First and reserved chunks are initialized with temporary allocation
 * map in initdata so that they can be used before slab is online.
 * This function is called after slab is brought up and replaces those
 * with properly allocated maps.
 */
void __init percpu_init_late(void)
{
        struct pcpu_chunk *target_chunks[] =
                { pcpu_first_chunk, pcpu_reserved_chunk, NULL };
        struct pcpu_chunk *chunk;
        unsigned long flags;
        int i;

        for (i = 0; (chunk = target_chunks[i]); i++) {
                int *map;
                const size_t size = PERCPU_DYNAMIC_EARLY_SLOTS * sizeof(map[0]);

                BUILD_BUG_ON(size > PAGE_SIZE);

                map = pcpu_mem_alloc(size);
                BUG_ON(!map);

                spin_lock_irqsave(&pcpu_lock, flags);
                memcpy(map, chunk->map, size);
                chunk->map = map;
                spin_unlock_irqrestore(&pcpu_lock, flags);
        }
}