// SPDX-License-Identifier: GPL-2.0-only
/*
 * Copyright (C) 2018 HUAWEI, Inc.
 *             http://www.huawei.com/
 * Created by Gao Xiang <gaoxiang25@huawei.com>
 */
#include "internal.h"
#include <linux/pagevec.h>

struct page *erofs_allocpage(struct list_head *pool, gfp_t gfp, bool nofail)
{
        struct page *page;

        if (!list_empty(pool)) {
                page = lru_to_page(pool);
                DBG_BUGON(page_ref_count(page) != 1);
                list_del(&page->lru);
        } else {
                page = alloc_pages(gfp | (nofail ? __GFP_NOFAIL : 0), 0);
        }
        return page;
}

#if (EROFS_PCPUBUF_NR_PAGES > 0)
static struct {
        u8 data[PAGE_SIZE * EROFS_PCPUBUF_NR_PAGES];
} ____cacheline_aligned_in_smp erofs_pcpubuf[NR_CPUS];

void *erofs_get_pcpubuf(unsigned int pagenr)
{
        preempt_disable();
        return &erofs_pcpubuf[smp_processor_id()].data[pagenr * PAGE_SIZE];
}
#endif

#ifdef CONFIG_EROFS_FS_ZIP
/* global shrink count (for all mounted EROFS instances) */
static atomic_long_t erofs_global_shrink_cnt;

#define __erofs_workgroup_get(grp)      atomic_inc(&(grp)->refcount)
#define __erofs_workgroup_put(grp)      atomic_dec(&(grp)->refcount)

static int erofs_workgroup_get(struct erofs_workgroup *grp)
{
        int o;

repeat:
        o = erofs_wait_on_workgroup_freezed(grp);
        if (o <= 0)
                return -1;

        if (atomic_cmpxchg(&grp->refcount, o, o + 1) != o)
                goto repeat;

        /* decrease refcount paired by erofs_workgroup_put */
        if (o == 1)
                atomic_long_dec(&erofs_global_shrink_cnt);
        return 0;
}

struct erofs_workgroup *erofs_find_workgroup(struct super_block *sb,
                                             pgoff_t index, bool *tag)
{
        struct erofs_sb_info *sbi = EROFS_SB(sb);
        struct erofs_workgroup *grp;

repeat:
        rcu_read_lock();
        grp = radix_tree_lookup(&sbi->workstn_tree, index);
        if (grp) {
                *tag = xa_pointer_tag(grp);
                grp = xa_untag_pointer(grp);

                if (erofs_workgroup_get(grp)) {
                        /* prefer to relax rcu read side */
                        rcu_read_unlock();
                        goto repeat;
                }

                DBG_BUGON(index != grp->index);
        }
        rcu_read_unlock();
        return grp;
}

int erofs_register_workgroup(struct super_block *sb,
                             struct erofs_workgroup *grp,
                             bool tag)
{
        struct erofs_sb_info *sbi;
        int err;

        /* grp shouldn't be broken or used before */
        if (atomic_read(&grp->refcount) != 1) {
                DBG_BUGON(1);
                return -EINVAL;
        }

        err = radix_tree_preload(GFP_NOFS);
        if (err)
                return err;

        sbi = EROFS_SB(sb);
        xa_lock(&sbi->workstn_tree);

        grp = xa_tag_pointer(grp, tag);

        /*
         * Bump up reference count before making this workgroup
         * visible to other users in order to avoid potential UAF
         * without serialized by workstn_lock.
         */
        __erofs_workgroup_get(grp);

        err = radix_tree_insert(&sbi->workstn_tree, grp->index, grp);
        if (err)
                /*
                 * it's safe to decrease since the workgroup isn't visible
                 * and refcount >= 2 (cannot be freezed).
                 */
                __erofs_workgroup_put(grp);

        xa_unlock(&sbi->workstn_tree);
        radix_tree_preload_end();
        return err;
}

static void  __erofs_workgroup_free(struct erofs_workgroup *grp)
{
        atomic_long_dec(&erofs_global_shrink_cnt);
        erofs_workgroup_free_rcu(grp);
}

int erofs_workgroup_put(struct erofs_workgroup *grp)
{
        int count = atomic_dec_return(&grp->refcount);

        if (count == 1)
                atomic_long_inc(&erofs_global_shrink_cnt);
        else if (!count)
                __erofs_workgroup_free(grp);
        return count;
}

static void erofs_workgroup_unfreeze_final(struct erofs_workgroup *grp)
{
        erofs_workgroup_unfreeze(grp, 0);
        __erofs_workgroup_free(grp);
}

static bool erofs_try_to_release_workgroup(struct erofs_sb_info *sbi,
                                           struct erofs_workgroup *grp,
                                           bool cleanup)
{
        /*
         * If managed cache is on, refcount of workgroups
         * themselves could be < 0 (freezed). In other words,
         * there is no guarantee that all refcounts > 0.
         */
        if (!erofs_workgroup_try_to_freeze(grp, 1))
                return false;

        /*
         * Note that all cached pages should be unattached
         * before deleted from the radix tree. Otherwise some
         * cached pages could be still attached to the orphan
         * old workgroup when the new one is available in the tree.
         */
        if (erofs_try_to_free_all_cached_pages(sbi, grp)) {
                erofs_workgroup_unfreeze(grp, 1);
                return false;
        }

        /*
         * It's impossible to fail after the workgroup is freezed,
         * however in order to avoid some race conditions, add a
         * DBG_BUGON to observe this in advance.
         */
        DBG_BUGON(xa_untag_pointer(radix_tree_delete(&sbi->workstn_tree,
                                                     grp->index)) != grp);

        /*
         * If managed cache is on, last refcount should indicate
         * the related workstation.
         */
        erofs_workgroup_unfreeze_final(grp);
        return true;
}

static unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
                                              unsigned long nr_shrink,
                                              bool cleanup)
{
        pgoff_t first_index = 0;
        void *batch[PAGEVEC_SIZE];
        unsigned int freed = 0;

        int i, found;
repeat:
        xa_lock(&sbi->workstn_tree);

        found = radix_tree_gang_lookup(&sbi->workstn_tree,
                                       batch, first_index, PAGEVEC_SIZE);

        for (i = 0; i < found; ++i) {
                struct erofs_workgroup *grp = xa_untag_pointer(batch[i]);

                first_index = grp->index + 1;

                /* try to shrink each valid workgroup */
                if (!erofs_try_to_release_workgroup(sbi, grp, cleanup))
                        continue;

                ++freed;
                if (!--nr_shrink)
                        break;
        }
        xa_unlock(&sbi->workstn_tree);

        if (i && nr_shrink)
                goto repeat;
        return freed;
}

/* protected by 'erofs_sb_list_lock' */
static unsigned int shrinker_run_no;

/* protects the mounted 'erofs_sb_list' */
static DEFINE_SPINLOCK(erofs_sb_list_lock);
static LIST_HEAD(erofs_sb_list);

void erofs_shrinker_register(struct super_block *sb)
{
        struct erofs_sb_info *sbi = EROFS_SB(sb);

        mutex_init(&sbi->umount_mutex);

        spin_lock(&erofs_sb_list_lock);
        list_add(&sbi->list, &erofs_sb_list);
        spin_unlock(&erofs_sb_list_lock);
}

void erofs_shrinker_unregister(struct super_block *sb)
{
        struct erofs_sb_info *const sbi = EROFS_SB(sb);

        mutex_lock(&sbi->umount_mutex);
        erofs_shrink_workstation(sbi, ~0UL, true);

        spin_lock(&erofs_sb_list_lock);
        list_del(&sbi->list);
        spin_unlock(&erofs_sb_list_lock);
        mutex_unlock(&sbi->umount_mutex);
}

static unsigned long erofs_shrink_count(struct shrinker *shrink,
                                        struct shrink_control *sc)
{
        return atomic_long_read(&erofs_global_shrink_cnt);
}

static unsigned long erofs_shrink_scan(struct shrinker *shrink,
                                       struct shrink_control *sc)
{
        struct erofs_sb_info *sbi;
        struct list_head *p;

        unsigned long nr = sc->nr_to_scan;
        unsigned int run_no;
        unsigned long freed = 0;

        spin_lock(&erofs_sb_list_lock);
        do {
                run_no = ++shrinker_run_no;
        } while (run_no == 0);

        /* Iterate over all mounted superblocks and try to shrink them */
        p = erofs_sb_list.next;
        while (p != &erofs_sb_list) {
                sbi = list_entry(p, struct erofs_sb_info, list);

                /*
                 * We move the ones we do to the end of the list, so we stop
                 * when we see one we have already done.
                 */
                if (sbi->shrinker_run_no == run_no)
                        break;

                if (!mutex_trylock(&sbi->umount_mutex)) {
                        p = p->next;
                        continue;
                }

                spin_unlock(&erofs_sb_list_lock);
                sbi->shrinker_run_no = run_no;

                freed += erofs_shrink_workstation(sbi, nr, false);

                spin_lock(&erofs_sb_list_lock);
                /* Get the next list element before we move this one */
                p = p->next;

                /*
                 * Move this one to the end of the list to provide some
                 * fairness.
                 */
                list_move_tail(&sbi->list, &erofs_sb_list);
                mutex_unlock(&sbi->umount_mutex);

                if (freed >= nr)
                        break;
        }
        spin_unlock(&erofs_sb_list_lock);
        return freed;
}

static struct shrinker erofs_shrinker_info = {
        .scan_objects = erofs_shrink_scan,
        .count_objects = erofs_shrink_count,
        .seeks = DEFAULT_SEEKS,
};

int __init erofs_init_shrinker(void)
{
        return register_shrinker(&erofs_shrinker_info);
}

void erofs_exit_shrinker(void)
{
        unregister_shrinker(&erofs_shrinker_info);
}
#endif  /* !CONFIG_EROFS_FS_ZIP */