/*
 * Copyright (C) 2016 Facebook
 * Copyright (C) 2013-2014 Jens Axboe
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <linux/sched.h>
#include <linux/random.h>
#include <linux/sbitmap.h>
#include <linux/seq_file.h>

/*
 * See if we have deferred clears that we can batch move
 */
static inline bool sbitmap_deferred_clear(struct sbitmap *sb, int index)
{
        unsigned long mask, val;
        bool ret = false;
        unsigned long flags;

        spin_lock_irqsave(&sb->map[index].swap_lock, flags);

        if (!sb->map[index].cleared)
                goto out_unlock;

        /*
         * First get a stable cleared mask, setting the old mask to 0.
         */
        do {
                mask = sb->map[index].cleared;
        } while (cmpxchg(&sb->map[index].cleared, mask, 0) != mask);

        /*
         * Now clear the masked bits in our free word
         */
        do {
                val = sb->map[index].word;
        } while (cmpxchg(&sb->map[index].word, val, val & ~mask) != val);

        ret = true;
out_unlock:
        spin_unlock_irqrestore(&sb->map[index].swap_lock, flags);
        return ret;
}

int sbitmap_init_node(struct sbitmap *sb, unsigned int depth, int shift,
                      gfp_t flags, int node)
{
        unsigned int bits_per_word;
        unsigned int i;

        if (shift < 0) {
                shift = ilog2(BITS_PER_LONG);
                /*
                 * If the bitmap is small, shrink the number of bits per word so
                 * we spread over a few cachelines, at least. If less than 4
                 * bits, just forget about it, it's not going to work optimally
                 * anyway.
                 */
                if (depth >= 4) {
                        while ((4U << shift) > depth)
                                shift--;
                }
        }
        bits_per_word = 1U << shift;
        if (bits_per_word > BITS_PER_LONG)
                return -EINVAL;

        sb->shift = shift;
        sb->depth = depth;
        sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);

        if (depth == 0) {
                sb->map = NULL;
                return 0;
        }

        sb->map = kcalloc_node(sb->map_nr, sizeof(*sb->map), flags, node);
        if (!sb->map)
                return -ENOMEM;

        for (i = 0; i < sb->map_nr; i++) {
                sb->map[i].depth = min(depth, bits_per_word);
                depth -= sb->map[i].depth;
                spin_lock_init(&sb->map[i].swap_lock);
        }
        return 0;
}
EXPORT_SYMBOL_GPL(sbitmap_init_node);

void sbitmap_resize(struct sbitmap *sb, unsigned int depth)
{
        unsigned int bits_per_word = 1U << sb->shift;
        unsigned int i;

        for (i = 0; i < sb->map_nr; i++)
                sbitmap_deferred_clear(sb, i);

        sb->depth = depth;
        sb->map_nr = DIV_ROUND_UP(sb->depth, bits_per_word);

        for (i = 0; i < sb->map_nr; i++) {
                sb->map[i].depth = min(depth, bits_per_word);
                depth -= sb->map[i].depth;
        }
}
EXPORT_SYMBOL_GPL(sbitmap_resize);

static int __sbitmap_get_word(unsigned long *word, unsigned long depth,
                              unsigned int hint, bool wrap)
{
        unsigned int orig_hint = hint;
        int nr;

        while (1) {
                nr = find_next_zero_bit(word, depth, hint);
                if (unlikely(nr >= depth)) {
                        /*
                         * We started with an offset, and we didn't reset the
                         * offset to 0 in a failure case, so start from 0 to
                         * exhaust the map.
                         */
                        if (orig_hint && hint && wrap) {
                                hint = orig_hint = 0;
                                continue;
                        }
                        return -1;
                }

                if (!test_and_set_bit_lock(nr, word))
                        break;

                hint = nr + 1;
                if (hint >= depth - 1)
                        hint = 0;
        }

        return nr;
}

static int sbitmap_find_bit_in_index(struct sbitmap *sb, int index,
                                     unsigned int alloc_hint, bool round_robin)
{
        int nr;

        do {
                nr = __sbitmap_get_word(&sb->map[index].word,
                                        sb->map[index].depth, alloc_hint,
                                        !round_robin);
                if (nr != -1)
                        break;
                if (!sbitmap_deferred_clear(sb, index))
                        break;
        } while (1);

        return nr;
}

int sbitmap_get(struct sbitmap *sb, unsigned int alloc_hint, bool round_robin)
{
        unsigned int i, index;
        int nr = -1;

        index = SB_NR_TO_INDEX(sb, alloc_hint);

        /*
         * Unless we're doing round robin tag allocation, just use the
         * alloc_hint to find the right word index. No point in looping
         * twice in find_next_zero_bit() for that case.
         */
        if (round_robin)
                alloc_hint = SB_NR_TO_BIT(sb, alloc_hint);
        else
                alloc_hint = 0;

        for (i = 0; i < sb->map_nr; i++) {
                nr = sbitmap_find_bit_in_index(sb, index, alloc_hint,
                                                round_robin);
                if (nr != -1) {
                        nr += index << sb->shift;
                        break;
                }

                /* Jump to next index. */
                alloc_hint = 0;
                if (++index >= sb->map_nr)
                        index = 0;
        }

        return nr;
}
EXPORT_SYMBOL_GPL(sbitmap_get);

int sbitmap_get_shallow(struct sbitmap *sb, unsigned int alloc_hint,
                        unsigned long shallow_depth)
{
        unsigned int i, index;
        int nr = -1;

        index = SB_NR_TO_INDEX(sb, alloc_hint);

        for (i = 0; i < sb->map_nr; i++) {
again:
                nr = __sbitmap_get_word(&sb->map[index].word,
                                        min(sb->map[index].depth, shallow_depth),
                                        SB_NR_TO_BIT(sb, alloc_hint), true);
                if (nr != -1) {
                        nr += index << sb->shift;
                        break;
                }

                if (sbitmap_deferred_clear(sb, index))
                        goto again;

                /* Jump to next index. */
                index++;
                alloc_hint = index << sb->shift;

                if (index >= sb->map_nr) {
                        index = 0;
                        alloc_hint = 0;
                }
        }

        return nr;
}
EXPORT_SYMBOL_GPL(sbitmap_get_shallow);

bool sbitmap_any_bit_set(const struct sbitmap *sb)
{
        unsigned int i;

        for (i = 0; i < sb->map_nr; i++) {
                if (sb->map[i].word & ~sb->map[i].cleared)
                        return true;
        }
        return false;
}
EXPORT_SYMBOL_GPL(sbitmap_any_bit_set);

bool sbitmap_any_bit_clear(const struct sbitmap *sb)
{
        unsigned int i;

        for (i = 0; i < sb->map_nr; i++) {
                const struct sbitmap_word *word = &sb->map[i];
                unsigned long mask = word->word & ~word->cleared;
                unsigned long ret;

                ret = find_first_zero_bit(&mask, word->depth);
                if (ret < word->depth)
                        return true;
        }
        return false;
}
EXPORT_SYMBOL_GPL(sbitmap_any_bit_clear);

static unsigned int __sbitmap_weight(const struct sbitmap *sb, bool set)
{
        unsigned int i, weight = 0;

        for (i = 0; i < sb->map_nr; i++) {
                const struct sbitmap_word *word = &sb->map[i];

                if (set)
                        weight += bitmap_weight(&word->word, word->depth);
                else
                        weight += bitmap_weight(&word->cleared, word->depth);
        }
        return weight;
}

static unsigned int sbitmap_weight(const struct sbitmap *sb)
{
        return __sbitmap_weight(sb, true);
}

static unsigned int sbitmap_cleared(const struct sbitmap *sb)
{
        return __sbitmap_weight(sb, false);
}

void sbitmap_show(struct sbitmap *sb, struct seq_file *m)
{
        seq_printf(m, "depth=%u\n", sb->depth);
        seq_printf(m, "busy=%u\n", sbitmap_weight(sb) - sbitmap_cleared(sb));
        seq_printf(m, "cleared=%u\n", sbitmap_cleared(sb));
        seq_printf(m, "bits_per_word=%u\n", 1U << sb->shift);
        seq_printf(m, "map_nr=%u\n", sb->map_nr);
}
EXPORT_SYMBOL_GPL(sbitmap_show);

static inline void emit_byte(struct seq_file *m, unsigned int offset, u8 byte)
{
        if ((offset & 0xf) == 0) {
                if (offset != 0)
                        seq_putc(m, '\n');
                seq_printf(m, "%08x:", offset);
        }
        if ((offset & 0x1) == 0)
                seq_putc(m, ' ');
        seq_printf(m, "%02x", byte);
}

void sbitmap_bitmap_show(struct sbitmap *sb, struct seq_file *m)
{
        u8 byte = 0;
        unsigned int byte_bits = 0;
        unsigned int offset = 0;
        int i;

        for (i = 0; i < sb->map_nr; i++) {
                unsigned long word = READ_ONCE(sb->map[i].word);
                unsigned int word_bits = READ_ONCE(sb->map[i].depth);

                while (word_bits > 0) {
                        unsigned int bits = min(8 - byte_bits, word_bits);

                        byte |= (word & (BIT(bits) - 1)) << byte_bits;
                        byte_bits += bits;
                        if (byte_bits == 8) {
                                emit_byte(m, offset, byte);
                                byte = 0;
                                byte_bits = 0;
                                offset++;
                        }
                        word >>= bits;
                        word_bits -= bits;
                }
        }
        if (byte_bits) {
                emit_byte(m, offset, byte);
                offset++;
        }
        if (offset)
                seq_putc(m, '\n');
}
EXPORT_SYMBOL_GPL(sbitmap_bitmap_show);

static unsigned int sbq_calc_wake_batch(struct sbitmap_queue *sbq,
                                        unsigned int depth)
{
        unsigned int wake_batch;
        unsigned int shallow_depth;

        /*
         * For each batch, we wake up one queue. We need to make sure that our
         * batch size is small enough that the full depth of the bitmap,
         * potentially limited by a shallow depth, is enough to wake up all of
         * the queues.
         *
         * Each full word of the bitmap has bits_per_word bits, and there might
         * be a partial word. There are depth / bits_per_word full words and
         * depth % bits_per_word bits left over. In bitwise arithmetic:
         *
         * bits_per_word = 1 << shift
         * depth / bits_per_word = depth >> shift
         * depth % bits_per_word = depth & ((1 << shift) - 1)
         *
         * Each word can be limited to sbq->min_shallow_depth bits.
         */
        shallow_depth = min(1U << sbq->sb.shift, sbq->min_shallow_depth);
        depth = ((depth >> sbq->sb.shift) * shallow_depth +
                 min(depth & ((1U << sbq->sb.shift) - 1), shallow_depth));
        wake_batch = clamp_t(unsigned int, depth / SBQ_WAIT_QUEUES, 1,
                             SBQ_WAKE_BATCH);

        return wake_batch;
}

int sbitmap_queue_init_node(struct sbitmap_queue *sbq, unsigned int depth,
                            int shift, bool round_robin, gfp_t flags, int node)
{
        int ret;
        int i;

        ret = sbitmap_init_node(&sbq->sb, depth, shift, flags, node);
        if (ret)
                return ret;

        sbq->alloc_hint = alloc_percpu_gfp(unsigned int, flags);
        if (!sbq->alloc_hint) {
                sbitmap_free(&sbq->sb);
                return -ENOMEM;
        }

        if (depth && !round_robin) {
                for_each_possible_cpu(i)
                        *per_cpu_ptr(sbq->alloc_hint, i) = prandom_u32() % depth;
        }

        sbq->min_shallow_depth = UINT_MAX;
        sbq->wake_batch = sbq_calc_wake_batch(sbq, depth);
        atomic_set(&sbq->wake_index, 0);
        atomic_set(&sbq->ws_active, 0);

        sbq->ws = kzalloc_node(SBQ_WAIT_QUEUES * sizeof(*sbq->ws), flags, node);
        if (!sbq->ws) {
                free_percpu(sbq->alloc_hint);
                sbitmap_free(&sbq->sb);
                return -ENOMEM;
        }

        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
                init_waitqueue_head(&sbq->ws[i].wait);
                atomic_set(&sbq->ws[i].wait_cnt, sbq->wake_batch);
        }

        sbq->round_robin = round_robin;
        return 0;
}
EXPORT_SYMBOL_GPL(sbitmap_queue_init_node);

static void sbitmap_queue_update_wake_batch(struct sbitmap_queue *sbq,
                                            unsigned int depth)
{
        unsigned int wake_batch = sbq_calc_wake_batch(sbq, depth);
        int i;

        if (sbq->wake_batch != wake_batch) {
                WRITE_ONCE(sbq->wake_batch, wake_batch);
                /*
                 * Pairs with the memory barrier in sbitmap_queue_wake_up()
                 * to ensure that the batch size is updated before the wait
                 * counts.
                 */
                smp_mb__before_atomic();
                for (i = 0; i < SBQ_WAIT_QUEUES; i++)
                        atomic_set(&sbq->ws[i].wait_cnt, 1);
        }
}

void sbitmap_queue_resize(struct sbitmap_queue *sbq, unsigned int depth)
{
        sbitmap_queue_update_wake_batch(sbq, depth);
        sbitmap_resize(&sbq->sb, depth);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_resize);

int __sbitmap_queue_get(struct sbitmap_queue *sbq)
{
        unsigned int hint, depth;
        int nr;

        hint = this_cpu_read(*sbq->alloc_hint);
        depth = READ_ONCE(sbq->sb.depth);
        if (unlikely(hint >= depth)) {
                hint = depth ? prandom_u32() % depth : 0;
                this_cpu_write(*sbq->alloc_hint, hint);
        }
        nr = sbitmap_get(&sbq->sb, hint, sbq->round_robin);

        if (nr == -1) {
                /* If the map is full, a hint won't do us much good. */
                this_cpu_write(*sbq->alloc_hint, 0);
        } else if (nr == hint || unlikely(sbq->round_robin)) {
                /* Only update the hint if we used it. */
                hint = nr + 1;
                if (hint >= depth - 1)
                        hint = 0;
                this_cpu_write(*sbq->alloc_hint, hint);
        }

        return nr;
}
EXPORT_SYMBOL_GPL(__sbitmap_queue_get);

int __sbitmap_queue_get_shallow(struct sbitmap_queue *sbq,
                                unsigned int shallow_depth)
{
        unsigned int hint, depth;
        int nr;

        WARN_ON_ONCE(shallow_depth < sbq->min_shallow_depth);

        hint = this_cpu_read(*sbq->alloc_hint);
        depth = READ_ONCE(sbq->sb.depth);
        if (unlikely(hint >= depth)) {
                hint = depth ? prandom_u32() % depth : 0;
                this_cpu_write(*sbq->alloc_hint, hint);
        }
        nr = sbitmap_get_shallow(&sbq->sb, hint, shallow_depth);

        if (nr == -1) {
                /* If the map is full, a hint won't do us much good. */
                this_cpu_write(*sbq->alloc_hint, 0);
        } else if (nr == hint || unlikely(sbq->round_robin)) {
                /* Only update the hint if we used it. */
                hint = nr + 1;
                if (hint >= depth - 1)
                        hint = 0;
                this_cpu_write(*sbq->alloc_hint, hint);
        }

        return nr;
}
EXPORT_SYMBOL_GPL(__sbitmap_queue_get_shallow);

void sbitmap_queue_min_shallow_depth(struct sbitmap_queue *sbq,
                                     unsigned int min_shallow_depth)
{
        sbq->min_shallow_depth = min_shallow_depth;
        sbitmap_queue_update_wake_batch(sbq, sbq->sb.depth);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_min_shallow_depth);

static struct sbq_wait_state *sbq_wake_ptr(struct sbitmap_queue *sbq)
{
        int i, wake_index;

        if (!atomic_read(&sbq->ws_active))
                return NULL;

        wake_index = atomic_read(&sbq->wake_index);
        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
                struct sbq_wait_state *ws = &sbq->ws[wake_index];

                if (waitqueue_active(&ws->wait)) {
                        int o = atomic_read(&sbq->wake_index);

                        if (wake_index != o)
                                atomic_cmpxchg(&sbq->wake_index, o, wake_index);
                        return ws;
                }

                wake_index = sbq_index_inc(wake_index);
        }

        return NULL;
}

static bool __sbq_wake_up(struct sbitmap_queue *sbq)
{
        struct sbq_wait_state *ws;
        unsigned int wake_batch;
        int wait_cnt;

        ws = sbq_wake_ptr(sbq);
        if (!ws)
                return false;

        wait_cnt = atomic_dec_return(&ws->wait_cnt);
        if (wait_cnt <= 0) {
                int ret;

                wake_batch = READ_ONCE(sbq->wake_batch);

                /*
                 * Pairs with the memory barrier in sbitmap_queue_resize() to
                 * ensure that we see the batch size update before the wait
                 * count is reset.
                 */
                smp_mb__before_atomic();

                /*
                 * For concurrent callers of this, the one that failed the
                 * atomic_cmpxhcg() race should call this function again
                 * to wakeup a new batch on a different 'ws'.
                 */
                ret = atomic_cmpxchg(&ws->wait_cnt, wait_cnt, wake_batch);
                if (ret == wait_cnt) {
                        sbq_index_atomic_inc(&sbq->wake_index);
                        wake_up_nr(&ws->wait, wake_batch);
                        return false;
                }

                return true;
        }

        return false;
}

void sbitmap_queue_wake_up(struct sbitmap_queue *sbq)
{
        while (__sbq_wake_up(sbq))
                ;
}
EXPORT_SYMBOL_GPL(sbitmap_queue_wake_up);

void sbitmap_queue_clear(struct sbitmap_queue *sbq, unsigned int nr,
                         unsigned int cpu)
{
        /*
         * Once the clear bit is set, the bit may be allocated out.
         *
         * Orders READ/WRITE on the asssociated instance(such as request
         * of blk_mq) by this bit for avoiding race with re-allocation,
         * and its pair is the memory barrier implied in __sbitmap_get_word.
         *
         * One invariant is that the clear bit has to be zero when the bit
         * is in use.
         */
        smp_mb__before_atomic();
        sbitmap_deferred_clear_bit(&sbq->sb, nr);

        /*
         * Pairs with the memory barrier in set_current_state() to ensure the
         * proper ordering of clear_bit_unlock()/waitqueue_active() in the waker
         * and test_and_set_bit_lock()/prepare_to_wait()/finish_wait() in the
         * waiter. See the comment on waitqueue_active().
         */
        smp_mb__after_atomic();
        sbitmap_queue_wake_up(sbq);

        if (likely(!sbq->round_robin && nr < sbq->sb.depth))
                *per_cpu_ptr(sbq->alloc_hint, cpu) = nr;
}
EXPORT_SYMBOL_GPL(sbitmap_queue_clear);

void sbitmap_queue_wake_all(struct sbitmap_queue *sbq)
{
        int i, wake_index;

        /*
         * Pairs with the memory barrier in set_current_state() like in
         * sbitmap_queue_wake_up().
         */
        smp_mb();
        wake_index = atomic_read(&sbq->wake_index);
        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
                struct sbq_wait_state *ws = &sbq->ws[wake_index];

                if (waitqueue_active(&ws->wait))
                        wake_up(&ws->wait);

                wake_index = sbq_index_inc(wake_index);
        }
}
EXPORT_SYMBOL_GPL(sbitmap_queue_wake_all);

void sbitmap_queue_show(struct sbitmap_queue *sbq, struct seq_file *m)
{
        bool first;
        int i;

        sbitmap_show(&sbq->sb, m);

        seq_puts(m, "alloc_hint={");
        first = true;
        for_each_possible_cpu(i) {
                if (!first)
                        seq_puts(m, ", ");
                first = false;
                seq_printf(m, "%u", *per_cpu_ptr(sbq->alloc_hint, i));
        }
        seq_puts(m, "}\n");

        seq_printf(m, "wake_batch=%u\n", sbq->wake_batch);
        seq_printf(m, "wake_index=%d\n", atomic_read(&sbq->wake_index));
        seq_printf(m, "ws_active=%d\n", atomic_read(&sbq->ws_active));

        seq_puts(m, "ws={\n");
        for (i = 0; i < SBQ_WAIT_QUEUES; i++) {
                struct sbq_wait_state *ws = &sbq->ws[i];

                seq_printf(m, "\t{.wait_cnt=%d, .wait=%s},\n",
                           atomic_read(&ws->wait_cnt),
                           waitqueue_active(&ws->wait) ? "active" : "inactive");
        }
        seq_puts(m, "}\n");

        seq_printf(m, "round_robin=%d\n", sbq->round_robin);
        seq_printf(m, "min_shallow_depth=%u\n", sbq->min_shallow_depth);
}
EXPORT_SYMBOL_GPL(sbitmap_queue_show);

void sbitmap_add_wait_queue(struct sbitmap_queue *sbq,
                            struct sbq_wait_state *ws,
                            struct sbq_wait *sbq_wait)
{
        if (!sbq_wait->sbq) {
                sbq_wait->sbq = sbq;
                atomic_inc(&sbq->ws_active);
        }
        add_wait_queue(&ws->wait, &sbq_wait->wait);
}
EXPORT_SYMBOL_GPL(sbitmap_add_wait_queue);

void sbitmap_del_wait_queue(struct sbq_wait *sbq_wait)
{
        list_del_init(&sbq_wait->wait.entry);
        if (sbq_wait->sbq) {
                atomic_dec(&sbq_wait->sbq->ws_active);
                sbq_wait->sbq = NULL;
        }
}
EXPORT_SYMBOL_GPL(sbitmap_del_wait_queue);

void sbitmap_prepare_to_wait(struct sbitmap_queue *sbq,
                             struct sbq_wait_state *ws,
                             struct sbq_wait *sbq_wait, int state)
{
        if (!sbq_wait->sbq) {
                atomic_inc(&sbq->ws_active);
                sbq_wait->sbq = sbq;
        }
        prepare_to_wait_exclusive(&ws->wait, &sbq_wait->wait, state);
}
EXPORT_SYMBOL_GPL(sbitmap_prepare_to_wait);

void sbitmap_finish_wait(struct sbitmap_queue *sbq, struct sbq_wait_state *ws,
                         struct sbq_wait *sbq_wait)
{
        finish_wait(&ws->wait, &sbq_wait->wait);
        if (sbq_wait->sbq) {
                atomic_dec(&sbq->ws_active);
                sbq_wait->sbq = NULL;
        }
}
EXPORT_SYMBOL_GPL(sbitmap_finish_wait);