xfs_iget.c

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/*
 * Copyright (c) 2000-2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would 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, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_types.h"
#include "xfs_acl.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_alloc_btree.h"
#include "xfs_ialloc_btree.h"
#include "xfs_dinode.h"
#include "xfs_inode.h"
#include "xfs_btree.h"
#include "xfs_ialloc.h"
#include "xfs_quota.h"
#include "xfs_utils.h"
#include "xfs_trans_priv.h"
#include "xfs_inode_item.h"
#include "xfs_bmap.h"
#include "xfs_trace.h"


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

    /*
     * if this didn't occur in transactions, we could use
     * KM_MAYFAIL and return NULL here on ENOMEM. Set the
     * code up to do this anyway.
     */
    ip = kmem_zone_alloc(xfs_inode_zone, KM_SLEEP);
    if (!ip)
        return NULL;
    if (inode_init_always(mp->m_super, VFS_I(ip))) {
        kmem_zone_free(xfs_inode_zone, ip);
        return NULL;
    }

    ASSERT(atomic_read(&ip->i_pincount) == 0);
    ASSERT(!spin_is_locked(&ip->i_flags_lock));
    ASSERT(!xfs_isiflocked(ip));
    ASSERT(ip->i_ino == 0);

    mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);

    /* 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;
    memset(&ip->i_df, 0, sizeof(xfs_ifork_t));
    ip->i_flags = 0;
    ip->i_delayed_blks = 0;
    memset(&ip->i_d, 0, sizeof(xfs_icdinode_t));

    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);

    kmem_zone_free(xfs_inode_zone, ip);
}

void
xfs_inode_free(
    struct xfs_inode    *ip)
{
    switch (ip->i_d.di_mode & S_IFMT) {
    case S_IFREG:
    case S_IFDIR:
    case S_IFLNK:
        xfs_idestroy_fork(ip, XFS_DATA_FORK);
        break;
    }

    if (ip->i_afp)
        xfs_idestroy_fork(ip, XFS_ATTR_FORK);

    if (ip->i_itemp) {
        ASSERT(!(ip->i_itemp->ili_item.li_flags & XFS_LI_IN_AIL));
        xfs_inode_item_destroy(ip);
        ip->i_itemp = NULL;
    }

    /* asserts to verify all state is correct here */
    ASSERT(atomic_read(&ip->i_pincount) == 0);
    ASSERT(!spin_is_locked(&ip->i_flags_lock));
    ASSERT(!xfs_isiflocked(ip));

    /*
     * 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);

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

/*
 * 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) {
        trace_xfs_iget_skip(ip);
        XFS_STATS_INC(xs_ig_frecycle);
        error = EAGAIN;
        goto out_error;
    }


    /*
     * If we are racing with another cache hit that is currently
     * instantiating this inode or currently recycling it out of
     * reclaimabe 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)) {
        trace_xfs_iget_skip(ip);
        XFS_STATS_INC(xs_ig_frecycle);
        error = EAGAIN;
        goto out_error;
    }

    /*
     * If lookup is racing with unlink return an error immediately.
     */
    if (ip->i_d.di_mode == 0 && !(flags & XFS_IGET_CREATE)) {
        error = ENOENT;
        goto out_error;
    }

    /*
     * If IRECLAIMABLE is set, we've torn down the VFS inode already.
     * Need to carefully get it back into useable state.
     */
    if (ip->i_flags & XFS_IRECLAIMABLE) {
        trace_xfs_iget_reclaim(ip);

        /*
         * We need to set XFS_IRECLAIM to prevent xfs_reclaim_inode
         * from stomping over us while we recycle the inode.  We can't
         * clear the radix tree reclaimable 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();

        error = -inode_init_always(mp->m_super, inode);
        if (error) {
            /*
             * 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);

            ip->i_flags &= ~(XFS_INEW | XFS_IRECLAIM);
            ASSERT(ip->i_flags & XFS_IRECLAIMABLE);
            trace_xfs_iget_reclaim_fail(ip);
            goto out_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_inode_clear_reclaim_tag(mp, pag, ip);
        inode->i_state = I_NEW;

        ASSERT(!rwsem_is_locked(&ip->i_iolock.mr_lock));
        mrlock_init(&ip->i_iolock, MRLOCK_BARRIER, "xfsio", ip->i_ino);

        spin_unlock(&ip->i_flags_lock);
        spin_unlock(&pag->pag_ici_lock);
    } else {
        /* If the VFS inode is being torn down, pause and try again. */
        if (!igrab(inode)) {
            trace_xfs_iget_skip(ip);
            error = EAGAIN;
            goto out_error;
        }

        /* 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);

    xfs_iflags_clear(ip, XFS_ISTALE | XFS_IDONTCACHE);
    XFS_STATS_INC(xs_ig_found);

    return 0;

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_iread(mp, tp, ip, flags);
    if (error)
        goto out_destroy;

    trace_xfs_iget_miss(ip);

    if ((ip->i_d.di_mode == 0) && !(flags & XFS_IGET_CREATE)) {
        error = ENOENT;
        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)
        iflags |= XFS_IDONTCACHE;
    ip->i_udquot = ip->i_gdquot = 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(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.
 * This flag parameter indicates how and if the inode's IO lock and inode lock
 * should be taken.
 *
 * mp -- the mount point structure for the current file system.  It points
 *       to the inode hash table.
 * tp -- a pointer to the current transaction if there is one.  This is
 *       simply passed through to the xfs_iread() call.
 * ino -- the number of the inode desired.  This is the unique identifier
 *        within the file system for the inode being requested.
 * lock_flags -- flags indicating how to lock the inode.  See the comment
 *       for xfs_ilock() for a list of valid values.
 */
int
xfs_iget(
    xfs_mount_t *mp,
    xfs_trans_t *tp,
    xfs_ino_t   ino,
    uint        flags,
    uint        lock_flags,
    xfs_inode_t **ipp)
{
    xfs_inode_t *ip;
    int     error;
    xfs_perag_t *pag;
    xfs_agino_t agino;

    /*
     * xfs_reclaim_inode() uses the ILOCK to ensure an inode
     * doesn't get freed while it's being referenced during a
     * radix tree traversal here.  It assumes this function
     * aqcuires only the ILOCK (and therefore it has no need to
     * involve the IOLOCK in this synchronization).
     */
    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;

    /* 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();
        XFS_STATS_INC(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 set ops(&unlock)
     * now.  If it's a new inode being created, xfs_ialloc will handle it.
     */
    if (xfs_iflags_test(ip, XFS_INEW) && ip->i_d.di_mode != 0)
        xfs_setup_inode(ip);
    return 0;

out_error_or_again:
    if (error == EAGAIN) {
        delay(1);
        goto again;
    }
    xfs_perag_put(pag);
    return error;
}

/*
 * This is a wrapper routine around the xfs_ilock() routine
 * used to centralize some grungy code.  It is used in places
 * that wish to lock the inode solely for reading the extents.
 * The reason these places can't just call xfs_ilock(SHARED)
 * is that the inode lock also guards to bringing in of the
 * extents from disk for a file in b-tree format.  If the inode
 * is in b-tree format, then we need to lock the inode exclusively
 * until the extents are read in.  Locking it exclusively all
 * the time would limit our parallelism unnecessarily, though.
 * What we do instead is check to see if the extents have been
 * read in yet, and only lock the inode exclusively if they
 * have not.
 *
 * The function returns a value which should be given to the
 * corresponding xfs_iunlock_map_shared().  This value is
 * the mode in which the lock was actually taken.
 */
uint
xfs_ilock_map_shared(
    xfs_inode_t *ip)
{
    uint    lock_mode;

    if ((ip->i_d.di_format == XFS_DINODE_FMT_BTREE) &&
        ((ip->i_df.if_flags & XFS_IFEXTENTS) == 0)) {
        lock_mode = XFS_ILOCK_EXCL;
    } else {
        lock_mode = XFS_ILOCK_SHARED;
    }

    xfs_ilock(ip, lock_mode);

    return lock_mode;
}

/*
 * This is simply the unlock routine to go with xfs_ilock_map_shared().
 * All it does is call xfs_iunlock() with the given lock_mode.
 */
void
xfs_iunlock_map_shared(
    xfs_inode_t *ip,
    unsigned int    lock_mode)
{
    xfs_iunlock(ip, lock_mode);
}

/*
 * The xfs inode contains 2 locks: a multi-reader lock called the
 * i_iolock and a multi-reader lock called the i_lock.  This routine
 * allows either or both of the locks to be obtained.
 *
 * The 2 locks should always be ordered so that the IO lock is
 * obtained first in order to prevent deadlock.
 *
 * ip -- the inode being locked
 * lock_flags -- this parameter indicates the inode's locks
 *       to be locked.  It can be:
 *      XFS_IOLOCK_SHARED,
 *      XFS_IOLOCK_EXCL,
 *      XFS_ILOCK_SHARED,
 *      XFS_ILOCK_EXCL,
 *      XFS_IOLOCK_SHARED | XFS_ILOCK_SHARED,
 *      XFS_IOLOCK_SHARED | XFS_ILOCK_EXCL,
 *      XFS_IOLOCK_EXCL | XFS_ILOCK_SHARED,
 *      XFS_IOLOCK_EXCL | XFS_ILOCK_EXCL
 */
void
xfs_ilock(
    xfs_inode_t     *ip,
    uint            lock_flags)
{
    /*
     * You can't set both SHARED and EXCL for the same lock,
     * and only XFS_IOLOCK_SHARED, XFS_IOLOCK_EXCL, XFS_ILOCK_SHARED,
     * and XFS_ILOCK_EXCL are valid values to set in lock_flags.
     */
    ASSERT((lock_flags & (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL)) !=
           (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
    ASSERT((lock_flags & (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL)) !=
           (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
    ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_DEP_MASK)) == 0);

    if (lock_flags & XFS_IOLOCK_EXCL)
        mrupdate_nested(&ip->i_iolock, XFS_IOLOCK_DEP(lock_flags));
    else if (lock_flags & XFS_IOLOCK_SHARED)
        mraccess_nested(&ip->i_iolock, XFS_IOLOCK_DEP(lock_flags));

    if (lock_flags & XFS_ILOCK_EXCL)
        mrupdate_nested(&ip->i_lock, XFS_ILOCK_DEP(lock_flags));
    else if (lock_flags & XFS_ILOCK_SHARED)
        mraccess_nested(&ip->i_lock, XFS_ILOCK_DEP(lock_flags));

    trace_xfs_ilock(ip, lock_flags, _RET_IP_);
}

/*
 * This is just like xfs_ilock(), except that the caller
 * is guaranteed not to sleep.  It returns 1 if it gets
 * the requested locks and 0 otherwise.  If the IO lock is
 * obtained but the inode lock cannot be, then the IO lock
 * is dropped before returning.
 *
 * ip -- the inode being locked
 * lock_flags -- this parameter indicates the inode's locks to be
 *       to be locked.  See the comment for xfs_ilock() for a list
 *   of valid values.
 */
int
xfs_ilock_nowait(
    xfs_inode_t     *ip,
    uint            lock_flags)
{
    /*
     * You can't set both SHARED and EXCL for the same lock,
     * and only XFS_IOLOCK_SHARED, XFS_IOLOCK_EXCL, XFS_ILOCK_SHARED,
     * and XFS_ILOCK_EXCL are valid values to set in lock_flags.
     */
    ASSERT((lock_flags & (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL)) !=
           (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
    ASSERT((lock_flags & (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL)) !=
           (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
    ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_DEP_MASK)) == 0);

    if (lock_flags & XFS_IOLOCK_EXCL) {
        if (!mrtryupdate(&ip->i_iolock))
            goto out;
    } else if (lock_flags & XFS_IOLOCK_SHARED) {
        if (!mrtryaccess(&ip->i_iolock))
            goto out;
    }
    if (lock_flags & XFS_ILOCK_EXCL) {
        if (!mrtryupdate(&ip->i_lock))
            goto out_undo_iolock;
    } else if (lock_flags & XFS_ILOCK_SHARED) {
        if (!mrtryaccess(&ip->i_lock))
            goto out_undo_iolock;
    }
    trace_xfs_ilock_nowait(ip, lock_flags, _RET_IP_);
    return 1;

 out_undo_iolock:
    if (lock_flags & XFS_IOLOCK_EXCL)
        mrunlock_excl(&ip->i_iolock);
    else if (lock_flags & XFS_IOLOCK_SHARED)
        mrunlock_shared(&ip->i_iolock);
 out:
    return 0;
}

/*
 * xfs_iunlock() is used to drop the inode locks acquired with
 * xfs_ilock() and xfs_ilock_nowait().  The caller must pass
 * in the flags given to xfs_ilock() or xfs_ilock_nowait() so
 * that we know which locks to drop.
 *
 * ip -- the inode being unlocked
 * lock_flags -- this parameter indicates the inode's locks to be
 *       to be unlocked.  See the comment for xfs_ilock() for a list
 *   of valid values for this parameter.
 *
 */
void
xfs_iunlock(
    xfs_inode_t     *ip,
    uint            lock_flags)
{
    /*
     * You can't set both SHARED and EXCL for the same lock,
     * and only XFS_IOLOCK_SHARED, XFS_IOLOCK_EXCL, XFS_ILOCK_SHARED,
     * and XFS_ILOCK_EXCL are valid values to set in lock_flags.
     */
    ASSERT((lock_flags & (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL)) !=
           (XFS_IOLOCK_SHARED | XFS_IOLOCK_EXCL));
    ASSERT((lock_flags & (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL)) !=
           (XFS_ILOCK_SHARED | XFS_ILOCK_EXCL));
    ASSERT((lock_flags & ~(XFS_LOCK_MASK | XFS_LOCK_DEP_MASK)) == 0);
    ASSERT(lock_flags != 0);

    if (lock_flags & XFS_IOLOCK_EXCL)
        mrunlock_excl(&ip->i_iolock);
    else if (lock_flags & XFS_IOLOCK_SHARED)
        mrunlock_shared(&ip->i_iolock);

    if (lock_flags & XFS_ILOCK_EXCL)
        mrunlock_excl(&ip->i_lock);
    else if (lock_flags & XFS_ILOCK_SHARED)
        mrunlock_shared(&ip->i_lock);

    trace_xfs_iunlock(ip, lock_flags, _RET_IP_);
}

/*
 * give up write locks.  the i/o lock cannot be held nested
 * if it is being demoted.
 */
void
xfs_ilock_demote(
    xfs_inode_t     *ip,
    uint            lock_flags)
{
    ASSERT(lock_flags & (XFS_IOLOCK_EXCL|XFS_ILOCK_EXCL));
    ASSERT((lock_flags & ~(XFS_IOLOCK_EXCL|XFS_ILOCK_EXCL)) == 0);

    if (lock_flags & XFS_ILOCK_EXCL)
        mrdemote(&ip->i_lock);
    if (lock_flags & XFS_IOLOCK_EXCL)
        mrdemote(&ip->i_iolock);

    trace_xfs_ilock_demote(ip, lock_flags, _RET_IP_);
}

#ifdef DEBUG
int
xfs_isilocked(
    xfs_inode_t     *ip,
    uint            lock_flags)
{
    if (lock_flags & (XFS_ILOCK_EXCL|XFS_ILOCK_SHARED)) {
        if (!(lock_flags & XFS_ILOCK_SHARED))
            return !!ip->i_lock.mr_writer;
        return rwsem_is_locked(&ip->i_lock.mr_lock);
    }

    if (lock_flags & (XFS_IOLOCK_EXCL|XFS_IOLOCK_SHARED)) {
        if (!(lock_flags & XFS_IOLOCK_SHARED))
            return !!ip->i_iolock.mr_writer;
        return rwsem_is_locked(&ip->i_iolock.mr_lock);
    }

    ASSERT(0);
    return 0;
}
#endif

void
__xfs_iflock(
    struct xfs_inode    *ip)
{
    wait_queue_head_t *wq = bit_waitqueue(&ip->i_flags, __XFS_IFLOCK_BIT);
    DEFINE_WAIT_BIT(wait, &ip->i_flags, __XFS_IFLOCK_BIT);

    do {
        prepare_to_wait_exclusive(wq, &wait.wait, TASK_UNINTERRUPTIBLE);
        if (xfs_isiflocked(ip))
            io_schedule();
    } while (!xfs_iflock_nowait(ip));

    finish_wait(wq, &wait.wait);
}