Merge branch 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git...

[linux-2.6-microblaze.git] / fs / xfs / xfs_icache.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_shared.h"
#include "xfs_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_inode.h"
#include "xfs_trans.h"
#include "xfs_trans_priv.h"
#include "xfs_inode_item.h"
#include "xfs_quota.h"
#include "xfs_trace.h"
#include "xfs_icache.h"
#include "xfs_bmap_util.h"
#include "xfs_dquot_item.h"
#include "xfs_dquot.h"
#include "xfs_reflink.h"
#include "xfs_ialloc.h"
#include "xfs_ag.h"

#include <linux/iversion.h>

/* Radix tree tags for incore inode tree. */

/* inode is to be reclaimed */
#define XFS_ICI_RECLAIM_TAG     0
/* Inode has speculative preallocations (posteof or cow) to clean. */
#define XFS_ICI_BLOCKGC_TAG     1

/*
 * The goal for walking incore inodes.  These can correspond with incore inode
 * radix tree tags when convenient.  Avoid existing XFS_IWALK namespace.
 */
enum xfs_icwalk_goal {
        /* Goals that are not related to tags; these must be < 0. */
        XFS_ICWALK_DQRELE       = -1,

        /* Goals directly associated with tagged inodes. */
        XFS_ICWALK_BLOCKGC      = XFS_ICI_BLOCKGC_TAG,
        XFS_ICWALK_RECLAIM      = XFS_ICI_RECLAIM_TAG,
};

#define XFS_ICWALK_NULL_TAG     (-1U)

/* Compute the inode radix tree tag for this goal. */
static inline unsigned int
xfs_icwalk_tag(enum xfs_icwalk_goal goal)
{
        return goal < 0 ? XFS_ICWALK_NULL_TAG : goal;
}

static int xfs_icwalk(struct xfs_mount *mp,
                enum xfs_icwalk_goal goal, struct xfs_icwalk *icw);
static int xfs_icwalk_ag(struct xfs_perag *pag,
                enum xfs_icwalk_goal goal, struct xfs_icwalk *icw);

/*
 * Private inode cache walk flags for struct xfs_icwalk.  Must not
 * coincide with XFS_ICWALK_FLAGS_VALID.
 */
#define XFS_ICWALK_FLAG_DROP_UDQUOT     (1U << 31)
#define XFS_ICWALK_FLAG_DROP_GDQUOT     (1U << 30)
#define XFS_ICWALK_FLAG_DROP_PDQUOT     (1U << 29)

/* Stop scanning after icw_scan_limit inodes. */
#define XFS_ICWALK_FLAG_SCAN_LIMIT      (1U << 28)

#define XFS_ICWALK_FLAG_RECLAIM_SICK    (1U << 27)
#define XFS_ICWALK_FLAG_UNION           (1U << 26) /* union filter algorithm */

#define XFS_ICWALK_PRIVATE_FLAGS        (XFS_ICWALK_FLAG_DROP_UDQUOT | \
                                         XFS_ICWALK_FLAG_DROP_GDQUOT | \
                                         XFS_ICWALK_FLAG_DROP_PDQUOT | \
                                         XFS_ICWALK_FLAG_SCAN_LIMIT | \
                                         XFS_ICWALK_FLAG_RECLAIM_SICK | \
                                         XFS_ICWALK_FLAG_UNION)

/*
 * Allocate and initialise an xfs_inode.
 */
struct xfs_inode *
xfs_inode_alloc(
        struct xfs_mount        *mp,
        xfs_ino_t               ino)
{
        struct xfs_inode        *ip;

        /*
         * XXX: If this didn't occur in transactions, we could drop GFP_NOFAIL
         * and return NULL here on ENOMEM.
         */
        ip = kmem_cache_alloc(xfs_inode_zone, GFP_KERNEL | __GFP_NOFAIL);

        if (inode_init_always(mp->m_super, VFS_I(ip))) {
                kmem_cache_free(xfs_inode_zone, ip);
                return NULL;
        }

        /* VFS doesn't initialise i_mode! */
        VFS_I(ip)->i_mode = 0;

        XFS_STATS_INC(mp, vn_active);
        ASSERT(atomic_read(&ip->i_pincount) == 0);
        ASSERT(ip->i_ino == 0);

        /* initialise the xfs inode */
        ip->i_ino = ino;
        ip->i_mount = mp;
        memset(&ip->i_imap, 0, sizeof(struct xfs_imap));
        ip->i_afp = NULL;
        ip->i_cowfp = NULL;
        memset(&ip->i_df, 0, sizeof(ip->i_df));
        ip->i_flags = 0;
        ip->i_delayed_blks = 0;
        ip->i_diflags2 = mp->m_ino_geo.new_diflags2;
        ip->i_nblocks = 0;
        ip->i_forkoff = 0;
        ip->i_sick = 0;
        ip->i_checked = 0;
        INIT_WORK(&ip->i_ioend_work, xfs_end_io);
        INIT_LIST_HEAD(&ip->i_ioend_list);
        spin_lock_init(&ip->i_ioend_lock);

        return ip;
}

STATIC void
xfs_inode_free_callback(
        struct rcu_head         *head)
{
        struct inode            *inode = container_of(head, struct inode, i_rcu);
        struct xfs_inode        *ip = XFS_I(inode);

        switch (VFS_I(ip)->i_mode & S_IFMT) {
        case S_IFREG:
        case S_IFDIR:
        case S_IFLNK:
                xfs_idestroy_fork(&ip->i_df);
                break;
        }

        if (ip->i_afp) {
                xfs_idestroy_fork(ip->i_afp);
                kmem_cache_free(xfs_ifork_zone, ip->i_afp);
        }
        if (ip->i_cowfp) {
                xfs_idestroy_fork(ip->i_cowfp);
                kmem_cache_free(xfs_ifork_zone, ip->i_cowfp);
        }
        if (ip->i_itemp) {
                ASSERT(!test_bit(XFS_LI_IN_AIL,
                                 &ip->i_itemp->ili_item.li_flags));
                xfs_inode_item_destroy(ip);
                ip->i_itemp = NULL;
        }

        kmem_cache_free(xfs_inode_zone, ip);
}

static void
__xfs_inode_free(
        struct xfs_inode        *ip)
{
        /* asserts to verify all state is correct here */
        ASSERT(atomic_read(&ip->i_pincount) == 0);
        ASSERT(!ip->i_itemp || list_empty(&ip->i_itemp->ili_item.li_bio_list));
        XFS_STATS_DEC(ip->i_mount, vn_active);

        call_rcu(&VFS_I(ip)->i_rcu, xfs_inode_free_callback);
}

void
xfs_inode_free(
        struct xfs_inode        *ip)
{
        ASSERT(!xfs_iflags_test(ip, XFS_IFLUSHING));

        /*
         * Because we use RCU freeing we need to ensure the inode always
         * appears to be reclaimed with an invalid inode number when in the
         * free state. The ip->i_flags_lock provides the barrier against lookup
         * races.
         */
        spin_lock(&ip->i_flags_lock);
        ip->i_flags = XFS_IRECLAIM;
        ip->i_ino = 0;
        spin_unlock(&ip->i_flags_lock);

        __xfs_inode_free(ip);
}

/*
 * Queue background inode reclaim work if there are reclaimable inodes and there
 * isn't reclaim work already scheduled or in progress.
 */
static void
xfs_reclaim_work_queue(
        struct xfs_mount        *mp)
{

        rcu_read_lock();
        if (radix_tree_tagged(&mp->m_perag_tree, XFS_ICI_RECLAIM_TAG)) {
                queue_delayed_work(mp->m_reclaim_workqueue, &mp->m_reclaim_work,
                        msecs_to_jiffies(xfs_syncd_centisecs / 6 * 10));
        }
        rcu_read_unlock();
}

/*
 * Background scanning to trim preallocated space. This is queued based on the
 * 'speculative_prealloc_lifetime' tunable (5m by default).
 */
static inline void
xfs_blockgc_queue(
        struct xfs_perag        *pag)
{
        rcu_read_lock();
        if (radix_tree_tagged(&pag->pag_ici_root, XFS_ICI_BLOCKGC_TAG))
                queue_delayed_work(pag->pag_mount->m_gc_workqueue,
                                   &pag->pag_blockgc_work,
                                   msecs_to_jiffies(xfs_blockgc_secs * 1000));
        rcu_read_unlock();
}

/* Set a tag on both the AG incore inode tree and the AG radix tree. */
static void
xfs_perag_set_inode_tag(
        struct xfs_perag        *pag,
        xfs_agino_t             agino,
        unsigned int            tag)
{
        struct xfs_mount        *mp = pag->pag_mount;
        bool                    was_tagged;

        lockdep_assert_held(&pag->pag_ici_lock);

        was_tagged = radix_tree_tagged(&pag->pag_ici_root, tag);
        radix_tree_tag_set(&pag->pag_ici_root, agino, tag);

        if (tag == XFS_ICI_RECLAIM_TAG)
                pag->pag_ici_reclaimable++;

        if (was_tagged)
                return;

        /* propagate the tag up into the perag radix tree */
        spin_lock(&mp->m_perag_lock);
        radix_tree_tag_set(&mp->m_perag_tree, pag->pag_agno, tag);
        spin_unlock(&mp->m_perag_lock);

        /* start background work */
        switch (tag) {
        case XFS_ICI_RECLAIM_TAG:
                xfs_reclaim_work_queue(mp);
                break;
        case XFS_ICI_BLOCKGC_TAG:
                xfs_blockgc_queue(pag);
                break;
        }

        trace_xfs_perag_set_inode_tag(mp, pag->pag_agno, tag, _RET_IP_);
}

/* Clear a tag on both the AG incore inode tree and the AG radix tree. */
static void
xfs_perag_clear_inode_tag(
        struct xfs_perag        *pag,
        xfs_agino_t             agino,
        unsigned int            tag)
{
        struct xfs_mount        *mp = pag->pag_mount;

        lockdep_assert_held(&pag->pag_ici_lock);

        /*
         * Reclaim can signal (with a null agino) that it cleared its own tag
         * by removing the inode from the radix tree.
         */
        if (agino != NULLAGINO)
                radix_tree_tag_clear(&pag->pag_ici_root, agino, tag);
        else
                ASSERT(tag == XFS_ICI_RECLAIM_TAG);

        if (tag == XFS_ICI_RECLAIM_TAG)
                pag->pag_ici_reclaimable--;

        if (radix_tree_tagged(&pag->pag_ici_root, tag))
                return;

        /* clear the tag from the perag radix tree */
        spin_lock(&mp->m_perag_lock);
        radix_tree_tag_clear(&mp->m_perag_tree, pag->pag_agno, tag);
        spin_unlock(&mp->m_perag_lock);

        trace_xfs_perag_clear_inode_tag(mp, pag->pag_agno, tag, _RET_IP_);
}

/*
 * We set the inode flag atomically with the radix tree tag.
 * Once we get tag lookups on the radix tree, this inode flag
 * can go away.
 */
void
xfs_inode_mark_reclaimable(
        struct xfs_inode        *ip)
{
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_perag        *pag;

        pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
        spin_lock(&pag->pag_ici_lock);
        spin_lock(&ip->i_flags_lock);

        xfs_perag_set_inode_tag(pag, XFS_INO_TO_AGINO(mp, ip->i_ino),
                        XFS_ICI_RECLAIM_TAG);
        __xfs_iflags_set(ip, XFS_IRECLAIMABLE);

        spin_unlock(&ip->i_flags_lock);
        spin_unlock(&pag->pag_ici_lock);
        xfs_perag_put(pag);
}

static inline void
xfs_inew_wait(
        struct xfs_inode        *ip)
{
        wait_queue_head_t *wq = bit_waitqueue(&ip->i_flags, __XFS_INEW_BIT);
        DEFINE_WAIT_BIT(wait, &ip->i_flags, __XFS_INEW_BIT);

        do {
                prepare_to_wait(wq, &wait.wq_entry, TASK_UNINTERRUPTIBLE);
                if (!xfs_iflags_test(ip, XFS_INEW))
                        break;
                schedule();
        } while (true);
        finish_wait(wq, &wait.wq_entry);
}

/*
 * When we recycle a reclaimable inode, we need to re-initialise the VFS inode
 * part of the structure. This is made more complex by the fact we store
 * information about the on-disk values in the VFS inode and so we can't just
 * overwrite the values unconditionally. Hence we save the parameters we
 * need to retain across reinitialisation, and rewrite them into the VFS inode
 * after reinitialisation even if it fails.
 */
static int
xfs_reinit_inode(
        struct xfs_mount        *mp,
        struct inode            *inode)
{
        int                     error;
        uint32_t                nlink = inode->i_nlink;
        uint32_t                generation = inode->i_generation;
        uint64_t                version = inode_peek_iversion(inode);
        umode_t                 mode = inode->i_mode;
        dev_t                   dev = inode->i_rdev;
        kuid_t                  uid = inode->i_uid;
        kgid_t                  gid = inode->i_gid;

        error = inode_init_always(mp->m_super, inode);

        set_nlink(inode, nlink);
        inode->i_generation = generation;
        inode_set_iversion_queried(inode, version);
        inode->i_mode = mode;
        inode->i_rdev = dev;
        inode->i_uid = uid;
        inode->i_gid = gid;
        return error;
}

/*
 * Carefully nudge an inode whose VFS state has been torn down back into a
 * usable state.  Drops the i_flags_lock and the rcu read lock.
 */
static int
xfs_iget_recycle(
        struct xfs_perag        *pag,
        struct xfs_inode        *ip) __releases(&ip->i_flags_lock)
{
        struct xfs_mount        *mp = ip->i_mount;
        struct inode            *inode = VFS_I(ip);
        int                     error;

        trace_xfs_iget_recycle(ip);

        /*
         * We need to make it look like the inode is being reclaimed to prevent
         * the actual reclaim workers from stomping over us while we recycle
         * the inode.  We can't clear the radix tree tag yet as it requires
         * pag_ici_lock to be held exclusive.
         */
        ip->i_flags |= XFS_IRECLAIM;

        spin_unlock(&ip->i_flags_lock);
        rcu_read_unlock();

        ASSERT(!rwsem_is_locked(&inode->i_rwsem));
        error = xfs_reinit_inode(mp, inode);
        if (error) {
                bool    wake;

                /*
                 * Re-initializing the inode failed, and we are in deep
                 * trouble.  Try to re-add it to the reclaim list.
                 */
                rcu_read_lock();
                spin_lock(&ip->i_flags_lock);
                wake = !!__xfs_iflags_test(ip, XFS_INEW);
                ip->i_flags &= ~(XFS_INEW | XFS_IRECLAIM);
                if (wake)
                        wake_up_bit(&ip->i_flags, __XFS_INEW_BIT);
                ASSERT(ip->i_flags & XFS_IRECLAIMABLE);
                spin_unlock(&ip->i_flags_lock);
                rcu_read_unlock();

                trace_xfs_iget_recycle_fail(ip);
                return error;
        }

        spin_lock(&pag->pag_ici_lock);
        spin_lock(&ip->i_flags_lock);

        /*
         * Clear the per-lifetime state in the inode as we are now effectively
         * a new inode and need to return to the initial state before reuse
         * occurs.
         */
        ip->i_flags &= ~XFS_IRECLAIM_RESET_FLAGS;
        ip->i_flags |= XFS_INEW;
        xfs_perag_clear_inode_tag(pag, XFS_INO_TO_AGINO(mp, ip->i_ino),
                        XFS_ICI_RECLAIM_TAG);
        inode->i_state = I_NEW;
        spin_unlock(&ip->i_flags_lock);
        spin_unlock(&pag->pag_ici_lock);

        return 0;
}

/*
 * If we are allocating a new inode, then check what was returned is
 * actually a free, empty inode. If we are not allocating an inode,
 * then check we didn't find a free inode.
 *
 * Returns:
 *      0               if the inode free state matches the lookup context
 *      -ENOENT         if the inode is free and we are not allocating
 *      -EFSCORRUPTED   if there is any state mismatch at all
 */
static int
xfs_iget_check_free_state(
        struct xfs_inode        *ip,
        int                     flags)
{
        if (flags & XFS_IGET_CREATE) {
                /* should be a free inode */
                if (VFS_I(ip)->i_mode != 0) {
                        xfs_warn(ip->i_mount,
"Corruption detected! Free inode 0x%llx not marked free! (mode 0x%x)",
                                ip->i_ino, VFS_I(ip)->i_mode);
                        return -EFSCORRUPTED;
                }

                if (ip->i_nblocks != 0) {
                        xfs_warn(ip->i_mount,
"Corruption detected! Free inode 0x%llx has blocks allocated!",
                                ip->i_ino);
                        return -EFSCORRUPTED;
                }
                return 0;
        }

        /* should be an allocated inode */
        if (VFS_I(ip)->i_mode == 0)
                return -ENOENT;

        return 0;
}

/*
 * Check the validity of the inode we just found it the cache
 */
static int
xfs_iget_cache_hit(
        struct xfs_perag        *pag,
        struct xfs_inode        *ip,
        xfs_ino_t               ino,
        int                     flags,
        int                     lock_flags) __releases(RCU)
{
        struct inode            *inode = VFS_I(ip);
        struct xfs_mount        *mp = ip->i_mount;
        int                     error;

        /*
         * check for re-use of an inode within an RCU grace period due to the
         * radix tree nodes not being updated yet. We monitor for this by
         * setting the inode number to zero before freeing the inode structure.
         * If the inode has been reallocated and set up, then the inode number
         * will not match, so check for that, too.
         */
        spin_lock(&ip->i_flags_lock);
        if (ip->i_ino != ino)
                goto out_skip;

        /*
         * If we are racing with another cache hit that is currently
         * instantiating this inode or currently recycling it out of
         * reclaimable state, wait for the initialisation to complete
         * before continuing.
         *
         * XXX(hch): eventually we should do something equivalent to
         *           wait_on_inode to wait for these flags to be cleared
         *           instead of polling for it.
         */
        if (ip->i_flags & (XFS_INEW | XFS_IRECLAIM))
                goto out_skip;

        /*
         * Check the inode free state is valid. This also detects lookup
         * racing with unlinks.
         */
        error = xfs_iget_check_free_state(ip, flags);
        if (error)
                goto out_error;

        /* Skip inodes that have no vfs state. */
        if ((flags & XFS_IGET_INCORE) &&
            (ip->i_flags & XFS_IRECLAIMABLE))
                goto out_skip;

        /* The inode fits the selection criteria; process it. */
        if (ip->i_flags & XFS_IRECLAIMABLE) {
                /* Drops i_flags_lock and RCU read lock. */
                error = xfs_iget_recycle(pag, ip);
                if (error)
                        return error;
        } else {
                /* If the VFS inode is being torn down, pause and try again. */
                if (!igrab(inode))
                        goto out_skip;

                /* We've got a live one. */
                spin_unlock(&ip->i_flags_lock);
                rcu_read_unlock();
                trace_xfs_iget_hit(ip);
        }

        if (lock_flags != 0)
                xfs_ilock(ip, lock_flags);

        if (!(flags & XFS_IGET_INCORE))
                xfs_iflags_clear(ip, XFS_ISTALE);
        XFS_STATS_INC(mp, xs_ig_found);

        return 0;

out_skip:
        trace_xfs_iget_skip(ip);
        XFS_STATS_INC(mp, xs_ig_frecycle);
        error = -EAGAIN;
out_error:
        spin_unlock(&ip->i_flags_lock);
        rcu_read_unlock();
        return error;
}

static int
xfs_iget_cache_miss(
        struct xfs_mount        *mp,
        struct xfs_perag        *pag,
        xfs_trans_t             *tp,
        xfs_ino_t               ino,
        struct xfs_inode        **ipp,
        int                     flags,
        int                     lock_flags)
{
        struct xfs_inode        *ip;
        int                     error;
        xfs_agino_t             agino = XFS_INO_TO_AGINO(mp, ino);
        int                     iflags;

        ip = xfs_inode_alloc(mp, ino);
        if (!ip)
                return -ENOMEM;

        error = xfs_imap(mp, tp, ip->i_ino, &ip->i_imap, flags);
        if (error)
                goto out_destroy;

        /*
         * For version 5 superblocks, if we are initialising a new inode and we
         * are not utilising the XFS_MOUNT_IKEEP inode cluster mode, we can
         * simply build the new inode core with a random generation number.
         *
         * For version 4 (and older) superblocks, log recovery is dependent on
         * the i_flushiter field being initialised from the current on-disk
         * value and hence we must also read the inode off disk even when
         * initializing new inodes.
         */
        if (xfs_sb_version_has_v3inode(&mp->m_sb) &&
            (flags & XFS_IGET_CREATE) && !(mp->m_flags & XFS_MOUNT_IKEEP)) {
                VFS_I(ip)->i_generation = prandom_u32();
        } else {
                struct xfs_buf          *bp;

                error = xfs_imap_to_bp(mp, tp, &ip->i_imap, &bp);
                if (error)
                        goto out_destroy;

                error = xfs_inode_from_disk(ip,
                                xfs_buf_offset(bp, ip->i_imap.im_boffset));
                if (!error)
                        xfs_buf_set_ref(bp, XFS_INO_REF);
                xfs_trans_brelse(tp, bp);

                if (error)
                        goto out_destroy;
        }

        trace_xfs_iget_miss(ip);

        /*
         * Check the inode free state is valid. This also detects lookup
         * racing with unlinks.
         */
        error = xfs_iget_check_free_state(ip, flags);
        if (error)
                goto out_destroy;

        /*
         * Preload the radix tree so we can insert safely under the
         * write spinlock. Note that we cannot sleep inside the preload
         * region. Since we can be called from transaction context, don't
         * recurse into the file system.
         */
        if (radix_tree_preload(GFP_NOFS)) {
                error = -EAGAIN;
                goto out_destroy;
        }

        /*
         * Because the inode hasn't been added to the radix-tree yet it can't
         * be found by another thread, so we can do the non-sleeping lock here.
         */
        if (lock_flags) {
                if (!xfs_ilock_nowait(ip, lock_flags))
                        BUG();
        }

        /*
         * These values must be set before inserting the inode into the radix
         * tree as the moment it is inserted a concurrent lookup (allowed by the
         * RCU locking mechanism) can find it and that lookup must see that this
         * is an inode currently under construction (i.e. that XFS_INEW is set).
         * The ip->i_flags_lock that protects the XFS_INEW flag forms the
         * memory barrier that ensures this detection works correctly at lookup
         * time.
         */
        iflags = XFS_INEW;
        if (flags & XFS_IGET_DONTCACHE)
                d_mark_dontcache(VFS_I(ip));
        ip->i_udquot = NULL;
        ip->i_gdquot = NULL;
        ip->i_pdquot = NULL;
        xfs_iflags_set(ip, iflags);

        /* insert the new inode */
        spin_lock(&pag->pag_ici_lock);
        error = radix_tree_insert(&pag->pag_ici_root, agino, ip);
        if (unlikely(error)) {
                WARN_ON(error != -EEXIST);
                XFS_STATS_INC(mp, xs_ig_dup);
                error = -EAGAIN;
                goto out_preload_end;
        }
        spin_unlock(&pag->pag_ici_lock);
        radix_tree_preload_end();

        *ipp = ip;
        return 0;

out_preload_end:
        spin_unlock(&pag->pag_ici_lock);
        radix_tree_preload_end();
        if (lock_flags)
                xfs_iunlock(ip, lock_flags);
out_destroy:
        __destroy_inode(VFS_I(ip));
        xfs_inode_free(ip);
        return error;
}

/*
 * Look up an inode by number in the given file system.  The inode is looked up
 * in the cache held in each AG.  If the inode is found in the cache, initialise
 * the vfs inode if necessary.
 *
 * If it is not in core, read it in from the file system's device, add it to the
 * cache and initialise the vfs inode.
 *
 * The inode is locked according to the value of the lock_flags parameter.
 * Inode lookup is only done during metadata operations and not as part of the
 * data IO path. Hence we only allow locking of the XFS_ILOCK during lookup.
 */
int
xfs_iget(
        struct xfs_mount        *mp,
        struct xfs_trans        *tp,
        xfs_ino_t               ino,
        uint                    flags,
        uint                    lock_flags,
        struct xfs_inode        **ipp)
{
        struct xfs_inode        *ip;
        struct xfs_perag        *pag;
        xfs_agino_t             agino;
        int                     error;

        ASSERT((lock_flags & (XFS_IOLOCK_EXCL | XFS_IOLOCK_SHARED)) == 0);

        /* reject inode numbers outside existing AGs */
        if (!ino || XFS_INO_TO_AGNO(mp, ino) >= mp->m_sb.sb_agcount)
                return -EINVAL;

        XFS_STATS_INC(mp, xs_ig_attempts);

        /* get the perag structure and ensure that it's inode capable */
        pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ino));
        agino = XFS_INO_TO_AGINO(mp, ino);

again:
        error = 0;
        rcu_read_lock();
        ip = radix_tree_lookup(&pag->pag_ici_root, agino);

        if (ip) {
                error = xfs_iget_cache_hit(pag, ip, ino, flags, lock_flags);
                if (error)
                        goto out_error_or_again;
        } else {
                rcu_read_unlock();
                if (flags & XFS_IGET_INCORE) {
                        error = -ENODATA;
                        goto out_error_or_again;
                }
                XFS_STATS_INC(mp, xs_ig_missed);

                error = xfs_iget_cache_miss(mp, pag, tp, ino, &ip,
                                                        flags, lock_flags);
                if (error)
                        goto out_error_or_again;
        }
        xfs_perag_put(pag);

        *ipp = ip;

        /*
         * If we have a real type for an on-disk inode, we can setup the inode
         * now.  If it's a new inode being created, xfs_ialloc will handle it.
         */
        if (xfs_iflags_test(ip, XFS_INEW) && VFS_I(ip)->i_mode != 0)
                xfs_setup_existing_inode(ip);
        return 0;

out_error_or_again:
        if (!(flags & XFS_IGET_INCORE) && error == -EAGAIN) {
                delay(1);
                goto again;
        }
        xfs_perag_put(pag);
        return error;
}

/*
 * "Is this a cached inode that's also allocated?"
 *
 * Look up an inode by number in the given file system.  If the inode is
 * in cache and isn't in purgatory, return 1 if the inode is allocated
 * and 0 if it is not.  For all other cases (not in cache, being torn
 * down, etc.), return a negative error code.
 *
 * The caller has to prevent inode allocation and freeing activity,
 * presumably by locking the AGI buffer.   This is to ensure that an
 * inode cannot transition from allocated to freed until the caller is
 * ready to allow that.  If the inode is in an intermediate state (new,
 * reclaimable, or being reclaimed), -EAGAIN will be returned; if the
 * inode is not in the cache, -ENOENT will be returned.  The caller must
 * deal with these scenarios appropriately.
 *
 * This is a specialized use case for the online scrubber; if you're
 * reading this, you probably want xfs_iget.
 */
int
xfs_icache_inode_is_allocated(
        struct xfs_mount        *mp,
        struct xfs_trans        *tp,
        xfs_ino_t               ino,
        bool                    *inuse)
{
        struct xfs_inode        *ip;
        int                     error;

        error = xfs_iget(mp, tp, ino, XFS_IGET_INCORE, 0, &ip);
        if (error)
                return error;

        *inuse = !!(VFS_I(ip)->i_mode);
        xfs_irele(ip);
        return 0;
}

#ifdef CONFIG_XFS_QUOTA
/* Decide if we want to grab this inode to drop its dquots. */
static bool
xfs_dqrele_igrab(
        struct xfs_inode        *ip)
{
        bool                    ret = false;

        ASSERT(rcu_read_lock_held());

        /* Check for stale RCU freed inode */
        spin_lock(&ip->i_flags_lock);
        if (!ip->i_ino)
                goto out_unlock;

        /*
         * Skip inodes that are anywhere in the reclaim machinery because we
         * drop dquots before tagging an inode for reclamation.
         */
        if (ip->i_flags & (XFS_IRECLAIM | XFS_IRECLAIMABLE))
                goto out_unlock;

        /*
         * The inode looks alive; try to grab a VFS reference so that it won't
         * get destroyed.  If we got the reference, return true to say that
         * we grabbed the inode.
         *
         * If we can't get the reference, then we know the inode had its VFS
         * state torn down and hasn't yet entered the reclaim machinery.  Since
         * we also know that dquots are detached from an inode before it enters
         * reclaim, we can skip the inode.
         */
        ret = igrab(VFS_I(ip)) != NULL;

out_unlock:
        spin_unlock(&ip->i_flags_lock);
        return ret;
}

/* Drop this inode's dquots. */
static void
xfs_dqrele_inode(
        struct xfs_inode        *ip,
        struct xfs_icwalk       *icw)
{
        if (xfs_iflags_test(ip, XFS_INEW))
                xfs_inew_wait(ip);

        xfs_ilock(ip, XFS_ILOCK_EXCL);
        if (icw->icw_flags & XFS_ICWALK_FLAG_DROP_UDQUOT) {
                xfs_qm_dqrele(ip->i_udquot);
                ip->i_udquot = NULL;
        }
        if (icw->icw_flags & XFS_ICWALK_FLAG_DROP_GDQUOT) {
                xfs_qm_dqrele(ip->i_gdquot);
                ip->i_gdquot = NULL;
        }
        if (icw->icw_flags & XFS_ICWALK_FLAG_DROP_PDQUOT) {
                xfs_qm_dqrele(ip->i_pdquot);
                ip->i_pdquot = NULL;
        }
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        xfs_irele(ip);
}

/*
 * Detach all dquots from incore inodes if we can.  The caller must already
 * have dropped the relevant XFS_[UGP]QUOTA_ACTIVE flags so that dquots will
 * not get reattached.
 */
int
xfs_dqrele_all_inodes(
        struct xfs_mount        *mp,
        unsigned int            qflags)
{
        struct xfs_icwalk       icw = { .icw_flags = 0 };

        if (qflags & XFS_UQUOTA_ACCT)
                icw.icw_flags |= XFS_ICWALK_FLAG_DROP_UDQUOT;
        if (qflags & XFS_GQUOTA_ACCT)
                icw.icw_flags |= XFS_ICWALK_FLAG_DROP_GDQUOT;
        if (qflags & XFS_PQUOTA_ACCT)
                icw.icw_flags |= XFS_ICWALK_FLAG_DROP_PDQUOT;

        return xfs_icwalk(mp, XFS_ICWALK_DQRELE, &icw);
}
#else
# define xfs_dqrele_igrab(ip)           (false)
# define xfs_dqrele_inode(ip, priv)     ((void)0)
#endif /* CONFIG_XFS_QUOTA */

/*
 * Grab the inode for reclaim exclusively.
 *
 * We have found this inode via a lookup under RCU, so the inode may have
 * already been freed, or it may be in the process of being recycled by
 * xfs_iget(). In both cases, the inode will have XFS_IRECLAIM set. If the inode
 * has been fully recycled by the time we get the i_flags_lock, XFS_IRECLAIMABLE
 * will not be set. Hence we need to check for both these flag conditions to
 * avoid inodes that are no longer reclaim candidates.
 *
 * Note: checking for other state flags here, under the i_flags_lock or not, is
 * racy and should be avoided. Those races should be resolved only after we have
 * ensured that we are able to reclaim this inode and the world can see that we
 * are going to reclaim it.
 *
 * Return true if we grabbed it, false otherwise.
 */
static bool
xfs_reclaim_igrab(
        struct xfs_inode        *ip,
        struct xfs_icwalk       *icw)
{
        ASSERT(rcu_read_lock_held());

        spin_lock(&ip->i_flags_lock);
        if (!__xfs_iflags_test(ip, XFS_IRECLAIMABLE) ||
            __xfs_iflags_test(ip, XFS_IRECLAIM)) {
                /* not a reclaim candidate. */
                spin_unlock(&ip->i_flags_lock);
                return false;
        }

        /* Don't reclaim a sick inode unless the caller asked for it. */
        if (ip->i_sick &&
            (!icw || !(icw->icw_flags & XFS_ICWALK_FLAG_RECLAIM_SICK))) {
                spin_unlock(&ip->i_flags_lock);
                return false;
        }

        __xfs_iflags_set(ip, XFS_IRECLAIM);
        spin_unlock(&ip->i_flags_lock);
        return true;
}

/*
 * Inode reclaim is non-blocking, so the default action if progress cannot be
 * made is to "requeue" the inode for reclaim by unlocking it and clearing the
 * XFS_IRECLAIM flag.  If we are in a shutdown state, we don't care about
 * blocking anymore and hence we can wait for the inode to be able to reclaim
 * it.
 *
 * We do no IO here - if callers require inodes to be cleaned they must push the
 * AIL first to trigger writeback of dirty inodes.  This enables writeback to be
 * done in the background in a non-blocking manner, and enables memory reclaim
 * to make progress without blocking.
 */
static void
xfs_reclaim_inode(
        struct xfs_inode        *ip,
        struct xfs_perag        *pag)
{
        xfs_ino_t               ino = ip->i_ino; /* for radix_tree_delete */

        if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL))
                goto out;
        if (xfs_iflags_test_and_set(ip, XFS_IFLUSHING))
                goto out_iunlock;

        if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                xfs_iunpin_wait(ip);
                xfs_iflush_abort(ip);
                goto reclaim;
        }
        if (xfs_ipincount(ip))
                goto out_clear_flush;
        if (!xfs_inode_clean(ip))
                goto out_clear_flush;

        xfs_iflags_clear(ip, XFS_IFLUSHING);
reclaim:

        /*
         * Because we use RCU freeing we need to ensure the inode always appears
         * to be reclaimed with an invalid inode number when in the free state.
         * We do this as early as possible under the ILOCK so that
         * xfs_iflush_cluster() and xfs_ifree_cluster() can be guaranteed to
         * detect races with us here. By doing this, we guarantee that once
         * xfs_iflush_cluster() or xfs_ifree_cluster() has locked XFS_ILOCK that
         * it will see either a valid inode that will serialise correctly, or it
         * will see an invalid inode that it can skip.
         */
        spin_lock(&ip->i_flags_lock);
        ip->i_flags = XFS_IRECLAIM;
        ip->i_ino = 0;
        ip->i_sick = 0;
        ip->i_checked = 0;
        spin_unlock(&ip->i_flags_lock);

        xfs_iunlock(ip, XFS_ILOCK_EXCL);

        XFS_STATS_INC(ip->i_mount, xs_ig_reclaims);
        /*
         * Remove the inode from the per-AG radix tree.
         *
         * Because radix_tree_delete won't complain even if the item was never
         * added to the tree assert that it's been there before to catch
         * problems with the inode life time early on.
         */
        spin_lock(&pag->pag_ici_lock);
        if (!radix_tree_delete(&pag->pag_ici_root,
                                XFS_INO_TO_AGINO(ip->i_mount, ino)))
                ASSERT(0);
        xfs_perag_clear_inode_tag(pag, NULLAGINO, XFS_ICI_RECLAIM_TAG);
        spin_unlock(&pag->pag_ici_lock);

        /*
         * Here we do an (almost) spurious inode lock in order to coordinate
         * with inode cache radix tree lookups.  This is because the lookup
         * can reference the inodes in the cache without taking references.
         *
         * We make that OK here by ensuring that we wait until the inode is
         * unlocked after the lookup before we go ahead and free it.
         */
        xfs_ilock(ip, XFS_ILOCK_EXCL);
        ASSERT(!ip->i_udquot && !ip->i_gdquot && !ip->i_pdquot);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        ASSERT(xfs_inode_clean(ip));

        __xfs_inode_free(ip);
        return;

out_clear_flush:
        xfs_iflags_clear(ip, XFS_IFLUSHING);
out_iunlock:
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
out:
        xfs_iflags_clear(ip, XFS_IRECLAIM);
}

/* Reclaim sick inodes if we're unmounting or the fs went down. */
static inline bool
xfs_want_reclaim_sick(
        struct xfs_mount        *mp)
{
        return (mp->m_flags & XFS_MOUNT_UNMOUNTING) ||
               (mp->m_flags & XFS_MOUNT_NORECOVERY) ||
               XFS_FORCED_SHUTDOWN(mp);
}

void
xfs_reclaim_inodes(
        struct xfs_mount        *mp)
{
        struct xfs_icwalk       icw = {
                .icw_flags      = 0,
        };

        if (xfs_want_reclaim_sick(mp))
                icw.icw_flags |= XFS_ICWALK_FLAG_RECLAIM_SICK;

        while (radix_tree_tagged(&mp->m_perag_tree, XFS_ICI_RECLAIM_TAG)) {
                xfs_ail_push_all_sync(mp->m_ail);
                xfs_icwalk(mp, XFS_ICWALK_RECLAIM, &icw);
        }
}

/*
 * The shrinker infrastructure determines how many inodes we should scan for
 * reclaim. We want as many clean inodes ready to reclaim as possible, so we
 * push the AIL here. We also want to proactively free up memory if we can to
 * minimise the amount of work memory reclaim has to do so we kick the
 * background reclaim if it isn't already scheduled.
 */
long
xfs_reclaim_inodes_nr(
        struct xfs_mount        *mp,
        unsigned long           nr_to_scan)
{
        struct xfs_icwalk       icw = {
                .icw_flags      = XFS_ICWALK_FLAG_SCAN_LIMIT,
                .icw_scan_limit = min_t(unsigned long, LONG_MAX, nr_to_scan),
        };

        if (xfs_want_reclaim_sick(mp))
                icw.icw_flags |= XFS_ICWALK_FLAG_RECLAIM_SICK;

        /* kick background reclaimer and push the AIL */
        xfs_reclaim_work_queue(mp);
        xfs_ail_push_all(mp->m_ail);

        xfs_icwalk(mp, XFS_ICWALK_RECLAIM, &icw);
        return 0;
}

/*
 * Return the number of reclaimable inodes in the filesystem for
 * the shrinker to determine how much to reclaim.
 */
long
xfs_reclaim_inodes_count(
        struct xfs_mount        *mp)
{
        struct xfs_perag        *pag;
        xfs_agnumber_t          ag = 0;
        long                    reclaimable = 0;

        while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
                ag = pag->pag_agno + 1;
                reclaimable += pag->pag_ici_reclaimable;
                xfs_perag_put(pag);
        }
        return reclaimable;
}

STATIC bool
xfs_icwalk_match_id(
        struct xfs_inode        *ip,
        struct xfs_icwalk       *icw)
{
        if ((icw->icw_flags & XFS_ICWALK_FLAG_UID) &&
            !uid_eq(VFS_I(ip)->i_uid, icw->icw_uid))
                return false;

        if ((icw->icw_flags & XFS_ICWALK_FLAG_GID) &&
            !gid_eq(VFS_I(ip)->i_gid, icw->icw_gid))
                return false;

        if ((icw->icw_flags & XFS_ICWALK_FLAG_PRID) &&
            ip->i_projid != icw->icw_prid)
                return false;

        return true;
}

/*
 * A union-based inode filtering algorithm. Process the inode if any of the
 * criteria match. This is for global/internal scans only.
 */
STATIC bool
xfs_icwalk_match_id_union(
        struct xfs_inode        *ip,
        struct xfs_icwalk       *icw)
{
        if ((icw->icw_flags & XFS_ICWALK_FLAG_UID) &&
            uid_eq(VFS_I(ip)->i_uid, icw->icw_uid))
                return true;

        if ((icw->icw_flags & XFS_ICWALK_FLAG_GID) &&
            gid_eq(VFS_I(ip)->i_gid, icw->icw_gid))
                return true;

        if ((icw->icw_flags & XFS_ICWALK_FLAG_PRID) &&
            ip->i_projid == icw->icw_prid)
                return true;

        return false;
}

/*
 * Is this inode @ip eligible for eof/cow block reclamation, given some
 * filtering parameters @icw?  The inode is eligible if @icw is null or
 * if the predicate functions match.
 */
static bool
xfs_icwalk_match(
        struct xfs_inode        *ip,
        struct xfs_icwalk       *icw)
{
        bool                    match;

        if (!icw)
                return true;

        if (icw->icw_flags & XFS_ICWALK_FLAG_UNION)
                match = xfs_icwalk_match_id_union(ip, icw);
        else
                match = xfs_icwalk_match_id(ip, icw);
        if (!match)
                return false;

        /* skip the inode if the file size is too small */
        if ((icw->icw_flags & XFS_ICWALK_FLAG_MINFILESIZE) &&
            XFS_ISIZE(ip) < icw->icw_min_file_size)
                return false;

        return true;
}

/*
 * This is a fast pass over the inode cache to try to get reclaim moving on as
 * many inodes as possible in a short period of time. It kicks itself every few
 * seconds, as well as being kicked by the inode cache shrinker when memory
 * goes low.
 */
void
xfs_reclaim_worker(
        struct work_struct *work)
{
        struct xfs_mount *mp = container_of(to_delayed_work(work),
                                        struct xfs_mount, m_reclaim_work);

        xfs_icwalk(mp, XFS_ICWALK_RECLAIM, NULL);
        xfs_reclaim_work_queue(mp);
}

STATIC int
xfs_inode_free_eofblocks(
        struct xfs_inode        *ip,
        struct xfs_icwalk       *icw,
        unsigned int            *lockflags)
{
        bool                    wait;

        wait = icw && (icw->icw_flags & XFS_ICWALK_FLAG_SYNC);

        if (!xfs_iflags_test(ip, XFS_IEOFBLOCKS))
                return 0;

        /*
         * If the mapping is dirty the operation can block and wait for some
         * time. Unless we are waiting, skip it.
         */
        if (!wait && mapping_tagged(VFS_I(ip)->i_mapping, PAGECACHE_TAG_DIRTY))
                return 0;

        if (!xfs_icwalk_match(ip, icw))
                return 0;

        /*
         * If the caller is waiting, return -EAGAIN to keep the background
         * scanner moving and revisit the inode in a subsequent pass.
         */
        if (!xfs_ilock_nowait(ip, XFS_IOLOCK_EXCL)) {
                if (wait)
                        return -EAGAIN;
                return 0;
        }
        *lockflags |= XFS_IOLOCK_EXCL;

        if (xfs_can_free_eofblocks(ip, false))
                return xfs_free_eofblocks(ip);

        /* inode could be preallocated or append-only */
        trace_xfs_inode_free_eofblocks_invalid(ip);
        xfs_inode_clear_eofblocks_tag(ip);
        return 0;
}

static void
xfs_blockgc_set_iflag(
        struct xfs_inode        *ip,
        unsigned long           iflag)
{
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_perag        *pag;

        ASSERT((iflag & ~(XFS_IEOFBLOCKS | XFS_ICOWBLOCKS)) == 0);

        /*
         * Don't bother locking the AG and looking up in the radix trees
         * if we already know that we have the tag set.
         */
        if (ip->i_flags & iflag)
                return;
        spin_lock(&ip->i_flags_lock);
        ip->i_flags |= iflag;
        spin_unlock(&ip->i_flags_lock);

        pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
        spin_lock(&pag->pag_ici_lock);

        xfs_perag_set_inode_tag(pag, XFS_INO_TO_AGINO(mp, ip->i_ino),
                        XFS_ICI_BLOCKGC_TAG);

        spin_unlock(&pag->pag_ici_lock);
        xfs_perag_put(pag);
}

void
xfs_inode_set_eofblocks_tag(
        xfs_inode_t     *ip)
{
        trace_xfs_inode_set_eofblocks_tag(ip);
        return xfs_blockgc_set_iflag(ip, XFS_IEOFBLOCKS);
}

static void
xfs_blockgc_clear_iflag(
        struct xfs_inode        *ip,
        unsigned long           iflag)
{
        struct xfs_mount        *mp = ip->i_mount;
        struct xfs_perag        *pag;
        bool                    clear_tag;

        ASSERT((iflag & ~(XFS_IEOFBLOCKS | XFS_ICOWBLOCKS)) == 0);

        spin_lock(&ip->i_flags_lock);
        ip->i_flags &= ~iflag;
        clear_tag = (ip->i_flags & (XFS_IEOFBLOCKS | XFS_ICOWBLOCKS)) == 0;
        spin_unlock(&ip->i_flags_lock);

        if (!clear_tag)
                return;

        pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
        spin_lock(&pag->pag_ici_lock);

        xfs_perag_clear_inode_tag(pag, XFS_INO_TO_AGINO(mp, ip->i_ino),
                        XFS_ICI_BLOCKGC_TAG);

        spin_unlock(&pag->pag_ici_lock);
        xfs_perag_put(pag);
}

void
xfs_inode_clear_eofblocks_tag(
        xfs_inode_t     *ip)
{
        trace_xfs_inode_clear_eofblocks_tag(ip);
        return xfs_blockgc_clear_iflag(ip, XFS_IEOFBLOCKS);
}

/*
 * Set ourselves up to free CoW blocks from this file.  If it's already clean
 * then we can bail out quickly, but otherwise we must back off if the file
 * is undergoing some kind of write.
 */
static bool
xfs_prep_free_cowblocks(
        struct xfs_inode        *ip)
{
        /*
         * Just clear the tag if we have an empty cow fork or none at all. It's
         * possible the inode was fully unshared since it was originally tagged.
         */
        if (!xfs_inode_has_cow_data(ip)) {
                trace_xfs_inode_free_cowblocks_invalid(ip);
                xfs_inode_clear_cowblocks_tag(ip);
                return false;
        }

        /*
         * If the mapping is dirty or under writeback we cannot touch the
         * CoW fork.  Leave it alone if we're in the midst of a directio.
         */
        if ((VFS_I(ip)->i_state & I_DIRTY_PAGES) ||
            mapping_tagged(VFS_I(ip)->i_mapping, PAGECACHE_TAG_DIRTY) ||
            mapping_tagged(VFS_I(ip)->i_mapping, PAGECACHE_TAG_WRITEBACK) ||
            atomic_read(&VFS_I(ip)->i_dio_count))
                return false;

        return true;
}

/*
 * Automatic CoW Reservation Freeing
 *
 * These functions automatically garbage collect leftover CoW reservations
 * that were made on behalf of a cowextsize hint when we start to run out
 * of quota or when the reservations sit around for too long.  If the file
 * has dirty pages or is undergoing writeback, its CoW reservations will
 * be retained.
 *
 * The actual garbage collection piggybacks off the same code that runs
 * the speculative EOF preallocation garbage collector.
 */
STATIC int
xfs_inode_free_cowblocks(
        struct xfs_inode        *ip,
        struct xfs_icwalk       *icw,
        unsigned int            *lockflags)
{
        bool                    wait;
        int                     ret = 0;

        wait = icw && (icw->icw_flags & XFS_ICWALK_FLAG_SYNC);

        if (!xfs_iflags_test(ip, XFS_ICOWBLOCKS))
                return 0;

        if (!xfs_prep_free_cowblocks(ip))
                return 0;

        if (!xfs_icwalk_match(ip, icw))
                return 0;

        /*
         * If the caller is waiting, return -EAGAIN to keep the background
         * scanner moving and revisit the inode in a subsequent pass.
         */
        if (!(*lockflags & XFS_IOLOCK_EXCL) &&
            !xfs_ilock_nowait(ip, XFS_IOLOCK_EXCL)) {
                if (wait)
                        return -EAGAIN;
                return 0;
        }
        *lockflags |= XFS_IOLOCK_EXCL;

        if (!xfs_ilock_nowait(ip, XFS_MMAPLOCK_EXCL)) {
                if (wait)
                        return -EAGAIN;
                return 0;
        }
        *lockflags |= XFS_MMAPLOCK_EXCL;

        /*
         * Check again, nobody else should be able to dirty blocks or change
         * the reflink iflag now that we have the first two locks held.
         */
        if (xfs_prep_free_cowblocks(ip))
                ret = xfs_reflink_cancel_cow_range(ip, 0, NULLFILEOFF, false);
        return ret;
}

void
xfs_inode_set_cowblocks_tag(
        xfs_inode_t     *ip)
{
        trace_xfs_inode_set_cowblocks_tag(ip);
        return xfs_blockgc_set_iflag(ip, XFS_ICOWBLOCKS);
}

void
xfs_inode_clear_cowblocks_tag(
        xfs_inode_t     *ip)
{
        trace_xfs_inode_clear_cowblocks_tag(ip);
        return xfs_blockgc_clear_iflag(ip, XFS_ICOWBLOCKS);
}

/* Disable post-EOF and CoW block auto-reclamation. */
void
xfs_blockgc_stop(
        struct xfs_mount        *mp)
{
        struct xfs_perag        *pag;
        xfs_agnumber_t          agno;

        for_each_perag_tag(mp, agno, pag, XFS_ICI_BLOCKGC_TAG)
                cancel_delayed_work_sync(&pag->pag_blockgc_work);
}

/* Enable post-EOF and CoW block auto-reclamation. */
void
xfs_blockgc_start(
        struct xfs_mount        *mp)
{
        struct xfs_perag        *pag;
        xfs_agnumber_t          agno;

        for_each_perag_tag(mp, agno, pag, XFS_ICI_BLOCKGC_TAG)
                xfs_blockgc_queue(pag);
}

/* Don't try to run block gc on an inode that's in any of these states. */
#define XFS_BLOCKGC_NOGRAB_IFLAGS       (XFS_INEW | \
                                         XFS_IRECLAIMABLE | \
                                         XFS_IRECLAIM)
/*
 * Decide if the given @ip is eligible for garbage collection of speculative
 * preallocations, and grab it if so.  Returns true if it's ready to go or
 * false if we should just ignore it.
 */
static bool
xfs_blockgc_igrab(
        struct xfs_inode        *ip)
{
        struct inode            *inode = VFS_I(ip);

        ASSERT(rcu_read_lock_held());

        /* Check for stale RCU freed inode */
        spin_lock(&ip->i_flags_lock);
        if (!ip->i_ino)
                goto out_unlock_noent;

        if (ip->i_flags & XFS_BLOCKGC_NOGRAB_IFLAGS)
                goto out_unlock_noent;
        spin_unlock(&ip->i_flags_lock);

        /* nothing to sync during shutdown */
        if (XFS_FORCED_SHUTDOWN(ip->i_mount))
                return false;

        /* If we can't grab the inode, it must on it's way to reclaim. */
        if (!igrab(inode))
                return false;

        /* inode is valid */
        return true;

out_unlock_noent:
        spin_unlock(&ip->i_flags_lock);
        return false;
}

/* Scan one incore inode for block preallocations that we can remove. */
static int
xfs_blockgc_scan_inode(
        struct xfs_inode        *ip,
        struct xfs_icwalk       *icw)
{
        unsigned int            lockflags = 0;
        int                     error;

        error = xfs_inode_free_eofblocks(ip, icw, &lockflags);
        if (error)
                goto unlock;

        error = xfs_inode_free_cowblocks(ip, icw, &lockflags);
unlock:
        if (lockflags)
                xfs_iunlock(ip, lockflags);
        xfs_irele(ip);
        return error;
}

/* Background worker that trims preallocated space. */
void
xfs_blockgc_worker(
        struct work_struct      *work)
{
        struct xfs_perag        *pag = container_of(to_delayed_work(work),
                                        struct xfs_perag, pag_blockgc_work);
        struct xfs_mount        *mp = pag->pag_mount;
        int                     error;

        if (!sb_start_write_trylock(mp->m_super))
                return;
        error = xfs_icwalk_ag(pag, XFS_ICWALK_BLOCKGC, NULL);
        if (error)
                xfs_info(mp, "AG %u preallocation gc worker failed, err=%d",
                                pag->pag_agno, error);
        sb_end_write(mp->m_super);
        xfs_blockgc_queue(pag);
}

/*
 * Try to free space in the filesystem by purging eofblocks and cowblocks.
 */
int
xfs_blockgc_free_space(
        struct xfs_mount        *mp,
        struct xfs_icwalk       *icw)
{
        trace_xfs_blockgc_free_space(mp, icw, _RET_IP_);

        return xfs_icwalk(mp, XFS_ICWALK_BLOCKGC, icw);
}

/*
 * Run cow/eofblocks scans on the supplied dquots.  We don't know exactly which
 * quota caused an allocation failure, so we make a best effort by including
 * each quota under low free space conditions (less than 1% free space) in the
 * scan.
 *
 * Callers must not hold any inode's ILOCK.  If requesting a synchronous scan
 * (XFS_ICWALK_FLAG_SYNC), the caller also must not hold any inode's IOLOCK or
 * MMAPLOCK.
 */
int
xfs_blockgc_free_dquots(
        struct xfs_mount        *mp,
        struct xfs_dquot        *udqp,
        struct xfs_dquot        *gdqp,
        struct xfs_dquot        *pdqp,
        unsigned int            iwalk_flags)
{
        struct xfs_icwalk       icw = {0};
        bool                    do_work = false;

        if (!udqp && !gdqp && !pdqp)
                return 0;

        /*
         * Run a scan to free blocks using the union filter to cover all
         * applicable quotas in a single scan.
         */
        icw.icw_flags = XFS_ICWALK_FLAG_UNION | iwalk_flags;

        if (XFS_IS_UQUOTA_ENFORCED(mp) && udqp && xfs_dquot_lowsp(udqp)) {
                icw.icw_uid = make_kuid(mp->m_super->s_user_ns, udqp->q_id);
                icw.icw_flags |= XFS_ICWALK_FLAG_UID;
                do_work = true;
        }

        if (XFS_IS_UQUOTA_ENFORCED(mp) && gdqp && xfs_dquot_lowsp(gdqp)) {
                icw.icw_gid = make_kgid(mp->m_super->s_user_ns, gdqp->q_id);
                icw.icw_flags |= XFS_ICWALK_FLAG_GID;
                do_work = true;
        }

        if (XFS_IS_PQUOTA_ENFORCED(mp) && pdqp && xfs_dquot_lowsp(pdqp)) {
                icw.icw_prid = pdqp->q_id;
                icw.icw_flags |= XFS_ICWALK_FLAG_PRID;
                do_work = true;
        }

        if (!do_work)
                return 0;

        return xfs_blockgc_free_space(mp, &icw);
}

/* Run cow/eofblocks scans on the quotas attached to the inode. */
int
xfs_blockgc_free_quota(
        struct xfs_inode        *ip,
        unsigned int            iwalk_flags)
{
        return xfs_blockgc_free_dquots(ip->i_mount,
                        xfs_inode_dquot(ip, XFS_DQTYPE_USER),
                        xfs_inode_dquot(ip, XFS_DQTYPE_GROUP),
                        xfs_inode_dquot(ip, XFS_DQTYPE_PROJ), iwalk_flags);
}

/* XFS Inode Cache Walking Code */

/*
 * The inode lookup is done in batches to keep the amount of lock traffic and
 * radix tree lookups to a minimum. The batch size is a trade off between
 * lookup reduction and stack usage. This is in the reclaim path, so we can't
 * be too greedy.
 */
#define XFS_LOOKUP_BATCH        32


/*
 * Decide if we want to grab this inode in anticipation of doing work towards
 * the goal.
 */
static inline bool
xfs_icwalk_igrab(
        enum xfs_icwalk_goal    goal,
        struct xfs_inode        *ip,
        struct xfs_icwalk       *icw)
{
        switch (goal) {
        case XFS_ICWALK_DQRELE:
                return xfs_dqrele_igrab(ip);
        case XFS_ICWALK_BLOCKGC:
                return xfs_blockgc_igrab(ip);
        case XFS_ICWALK_RECLAIM:
                return xfs_reclaim_igrab(ip, icw);
        default:
                return false;
        }
}

/*
 * Process an inode.  Each processing function must handle any state changes
 * made by the icwalk igrab function.  Return -EAGAIN to skip an inode.
 */
static inline int
xfs_icwalk_process_inode(
        enum xfs_icwalk_goal    goal,
        struct xfs_inode        *ip,
        struct xfs_perag        *pag,
        struct xfs_icwalk       *icw)
{
        int                     error = 0;

        switch (goal) {
        case XFS_ICWALK_DQRELE:
                xfs_dqrele_inode(ip, icw);
                break;
        case XFS_ICWALK_BLOCKGC:
                error = xfs_blockgc_scan_inode(ip, icw);
                break;
        case XFS_ICWALK_RECLAIM:
                xfs_reclaim_inode(ip, pag);
                break;
        }
        return error;
}

/*
 * For a given per-AG structure @pag and a goal, grab qualifying inodes and
 * process them in some manner.
 */
static int
xfs_icwalk_ag(
        struct xfs_perag        *pag,
        enum xfs_icwalk_goal    goal,
        struct xfs_icwalk       *icw)
{
        struct xfs_mount        *mp = pag->pag_mount;
        uint32_t                first_index;
        int                     last_error = 0;
        int                     skipped;
        bool                    done;
        int                     nr_found;

restart:
        done = false;
        skipped = 0;
        if (goal == XFS_ICWALK_RECLAIM)
                first_index = READ_ONCE(pag->pag_ici_reclaim_cursor);
        else
                first_index = 0;
        nr_found = 0;
        do {
                struct xfs_inode *batch[XFS_LOOKUP_BATCH];
                unsigned int    tag = xfs_icwalk_tag(goal);
                int             error = 0;
                int             i;

                rcu_read_lock();

                if (tag == XFS_ICWALK_NULL_TAG)
                        nr_found = radix_tree_gang_lookup(&pag->pag_ici_root,
                                        (void **)batch, first_index,
                                        XFS_LOOKUP_BATCH);
                else
                        nr_found = radix_tree_gang_lookup_tag(
                                        &pag->pag_ici_root,
                                        (void **) batch, first_index,
                                        XFS_LOOKUP_BATCH, tag);

                if (!nr_found) {
                        done = true;
                        rcu_read_unlock();
                        break;
                }

                /*
                 * Grab the inodes before we drop the lock. if we found
                 * nothing, nr == 0 and the loop will be skipped.
                 */
                for (i = 0; i < nr_found; i++) {
                        struct xfs_inode *ip = batch[i];

                        if (done || !xfs_icwalk_igrab(goal, ip, icw))
                                batch[i] = NULL;

                        /*
                         * Update the index for the next lookup. Catch
                         * overflows into the next AG range which can occur if
                         * we have inodes in the last block of the AG and we
                         * are currently pointing to the last inode.
                         *
                         * Because we may see inodes that are from the wrong AG
                         * due to RCU freeing and reallocation, only update the
                         * index if it lies in this AG. It was a race that lead
                         * us to see this inode, so another lookup from the
                         * same index will not find it again.
                         */
                        if (XFS_INO_TO_AGNO(mp, ip->i_ino) != pag->pag_agno)
                                continue;
                        first_index = XFS_INO_TO_AGINO(mp, ip->i_ino + 1);
                        if (first_index < XFS_INO_TO_AGINO(mp, ip->i_ino))
                                done = true;
                }

                /* unlock now we've grabbed the inodes. */
                rcu_read_unlock();

                for (i = 0; i < nr_found; i++) {
                        if (!batch[i])
                                continue;
                        error = xfs_icwalk_process_inode(goal, batch[i], pag,
                                        icw);
                        if (error == -EAGAIN) {
                                skipped++;
                                continue;
                        }
                        if (error && last_error != -EFSCORRUPTED)
                                last_error = error;
                }

                /* bail out if the filesystem is corrupted.  */
                if (error == -EFSCORRUPTED)
                        break;

                cond_resched();

                if (icw && (icw->icw_flags & XFS_ICWALK_FLAG_SCAN_LIMIT)) {
                        icw->icw_scan_limit -= XFS_LOOKUP_BATCH;
                        if (icw->icw_scan_limit <= 0)
                                break;
                }
        } while (nr_found && !done);

        if (goal == XFS_ICWALK_RECLAIM) {
                if (done)
                        first_index = 0;
                WRITE_ONCE(pag->pag_ici_reclaim_cursor, first_index);
        }

        if (skipped) {
                delay(1);
                goto restart;
        }
        return last_error;
}

/* Fetch the next (possibly tagged) per-AG structure. */
static inline struct xfs_perag *
xfs_icwalk_get_perag(
        struct xfs_mount        *mp,
        xfs_agnumber_t          agno,
        enum xfs_icwalk_goal    goal)
{
        unsigned int            tag = xfs_icwalk_tag(goal);

        if (tag == XFS_ICWALK_NULL_TAG)
                return xfs_perag_get(mp, agno);
        return xfs_perag_get_tag(mp, agno, tag);
}

/* Walk all incore inodes to achieve a given goal. */
static int
xfs_icwalk(
        struct xfs_mount        *mp,
        enum xfs_icwalk_goal    goal,
        struct xfs_icwalk       *icw)
{
        struct xfs_perag        *pag;
        int                     error = 0;
        int                     last_error = 0;
        xfs_agnumber_t          agno = 0;

        while ((pag = xfs_icwalk_get_perag(mp, agno, goal))) {
                agno = pag->pag_agno + 1;
                error = xfs_icwalk_ag(pag, goal, icw);
                xfs_perag_put(pag);
                if (error) {
                        last_error = error;
                        if (error == -EFSCORRUPTED)
                                break;
                }
        }
        return last_error;
        BUILD_BUG_ON(XFS_ICWALK_PRIVATE_FLAGS & XFS_ICWALK_FLAGS_VALID);
}