memcg: fix Bad page state after replace_page_cache

[zen-stable.git] / fs / xfs / xfs_dquot.c

/*
 * Copyright (c) 2000-2003 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_bit.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_alloc.h"
#include "xfs_quota.h"
#include "xfs_mount.h"
#include "xfs_bmap_btree.h"
#include "xfs_inode.h"
#include "xfs_bmap.h"
#include "xfs_rtalloc.h"
#include "xfs_error.h"
#include "xfs_itable.h"
#include "xfs_attr.h"
#include "xfs_buf_item.h"
#include "xfs_trans_space.h"
#include "xfs_trans_priv.h"
#include "xfs_qm.h"
#include "xfs_trace.h"

/*
 * Lock order:
 *
 * ip->i_lock
 *   qh->qh_lock
 *     qi->qi_dqlist_lock
 *       dquot->q_qlock (xfs_dqlock() and friends)
 *         dquot->q_flush (xfs_dqflock() and friends)
 *         xfs_Gqm->qm_dqfrlist_lock
 *
 * If two dquots need to be locked the order is user before group/project,
 * otherwise by the lowest id first, see xfs_dqlock2.
 */

#ifdef DEBUG
xfs_buftarg_t *xfs_dqerror_target;
int xfs_do_dqerror;
int xfs_dqreq_num;
int xfs_dqerror_mod = 33;
#endif

static struct lock_class_key xfs_dquot_other_class;

/*
 * This is called to free all the memory associated with a dquot
 */
void
xfs_qm_dqdestroy(
        xfs_dquot_t     *dqp)
{
        ASSERT(list_empty(&dqp->q_freelist));

        mutex_destroy(&dqp->q_qlock);
        kmem_zone_free(xfs_Gqm->qm_dqzone, dqp);

        atomic_dec(&xfs_Gqm->qm_totaldquots);
}

/*
 * If default limits are in force, push them into the dquot now.
 * We overwrite the dquot limits only if they are zero and this
 * is not the root dquot.
 */
void
xfs_qm_adjust_dqlimits(
        xfs_mount_t             *mp,
        xfs_disk_dquot_t        *d)
{
        xfs_quotainfo_t         *q = mp->m_quotainfo;

        ASSERT(d->d_id);

        if (q->qi_bsoftlimit && !d->d_blk_softlimit)
                d->d_blk_softlimit = cpu_to_be64(q->qi_bsoftlimit);
        if (q->qi_bhardlimit && !d->d_blk_hardlimit)
                d->d_blk_hardlimit = cpu_to_be64(q->qi_bhardlimit);
        if (q->qi_isoftlimit && !d->d_ino_softlimit)
                d->d_ino_softlimit = cpu_to_be64(q->qi_isoftlimit);
        if (q->qi_ihardlimit && !d->d_ino_hardlimit)
                d->d_ino_hardlimit = cpu_to_be64(q->qi_ihardlimit);
        if (q->qi_rtbsoftlimit && !d->d_rtb_softlimit)
                d->d_rtb_softlimit = cpu_to_be64(q->qi_rtbsoftlimit);
        if (q->qi_rtbhardlimit && !d->d_rtb_hardlimit)
                d->d_rtb_hardlimit = cpu_to_be64(q->qi_rtbhardlimit);
}

/*
 * Check the limits and timers of a dquot and start or reset timers
 * if necessary.
 * This gets called even when quota enforcement is OFF, which makes our
 * life a little less complicated. (We just don't reject any quota
 * reservations in that case, when enforcement is off).
 * We also return 0 as the values of the timers in Q_GETQUOTA calls, when
 * enforcement's off.
 * In contrast, warnings are a little different in that they don't
 * 'automatically' get started when limits get exceeded.  They do
 * get reset to zero, however, when we find the count to be under
 * the soft limit (they are only ever set non-zero via userspace).
 */
void
xfs_qm_adjust_dqtimers(
        xfs_mount_t             *mp,
        xfs_disk_dquot_t        *d)
{
        ASSERT(d->d_id);

#ifdef DEBUG
        if (d->d_blk_hardlimit)
                ASSERT(be64_to_cpu(d->d_blk_softlimit) <=
                       be64_to_cpu(d->d_blk_hardlimit));
        if (d->d_ino_hardlimit)
                ASSERT(be64_to_cpu(d->d_ino_softlimit) <=
                       be64_to_cpu(d->d_ino_hardlimit));
        if (d->d_rtb_hardlimit)
                ASSERT(be64_to_cpu(d->d_rtb_softlimit) <=
                       be64_to_cpu(d->d_rtb_hardlimit));
#endif

        if (!d->d_btimer) {
                if ((d->d_blk_softlimit &&
                     (be64_to_cpu(d->d_bcount) >
                      be64_to_cpu(d->d_blk_softlimit))) ||
                    (d->d_blk_hardlimit &&
                     (be64_to_cpu(d->d_bcount) >
                      be64_to_cpu(d->d_blk_hardlimit)))) {
                        d->d_btimer = cpu_to_be32(get_seconds() +
                                        mp->m_quotainfo->qi_btimelimit);
                } else {
                        d->d_bwarns = 0;
                }
        } else {
                if ((!d->d_blk_softlimit ||
                     (be64_to_cpu(d->d_bcount) <=
                      be64_to_cpu(d->d_blk_softlimit))) &&
                    (!d->d_blk_hardlimit ||
                    (be64_to_cpu(d->d_bcount) <=
                     be64_to_cpu(d->d_blk_hardlimit)))) {
                        d->d_btimer = 0;
                }
        }

        if (!d->d_itimer) {
                if ((d->d_ino_softlimit &&
                     (be64_to_cpu(d->d_icount) >
                      be64_to_cpu(d->d_ino_softlimit))) ||
                    (d->d_ino_hardlimit &&
                     (be64_to_cpu(d->d_icount) >
                      be64_to_cpu(d->d_ino_hardlimit)))) {
                        d->d_itimer = cpu_to_be32(get_seconds() +
                                        mp->m_quotainfo->qi_itimelimit);
                } else {
                        d->d_iwarns = 0;
                }
        } else {
                if ((!d->d_ino_softlimit ||
                     (be64_to_cpu(d->d_icount) <=
                      be64_to_cpu(d->d_ino_softlimit)))  &&
                    (!d->d_ino_hardlimit ||
                     (be64_to_cpu(d->d_icount) <=
                      be64_to_cpu(d->d_ino_hardlimit)))) {
                        d->d_itimer = 0;
                }
        }

        if (!d->d_rtbtimer) {
                if ((d->d_rtb_softlimit &&
                     (be64_to_cpu(d->d_rtbcount) >
                      be64_to_cpu(d->d_rtb_softlimit))) ||
                    (d->d_rtb_hardlimit &&
                     (be64_to_cpu(d->d_rtbcount) >
                      be64_to_cpu(d->d_rtb_hardlimit)))) {
                        d->d_rtbtimer = cpu_to_be32(get_seconds() +
                                        mp->m_quotainfo->qi_rtbtimelimit);
                } else {
                        d->d_rtbwarns = 0;
                }
        } else {
                if ((!d->d_rtb_softlimit ||
                     (be64_to_cpu(d->d_rtbcount) <=
                      be64_to_cpu(d->d_rtb_softlimit))) &&
                    (!d->d_rtb_hardlimit ||
                     (be64_to_cpu(d->d_rtbcount) <=
                      be64_to_cpu(d->d_rtb_hardlimit)))) {
                        d->d_rtbtimer = 0;
                }
        }
}

/*
 * initialize a buffer full of dquots and log the whole thing
 */
STATIC void
xfs_qm_init_dquot_blk(
        xfs_trans_t     *tp,
        xfs_mount_t     *mp,
        xfs_dqid_t      id,
        uint            type,
        xfs_buf_t       *bp)
{
        struct xfs_quotainfo    *q = mp->m_quotainfo;
        xfs_dqblk_t     *d;
        int             curid, i;

        ASSERT(tp);
        ASSERT(xfs_buf_islocked(bp));

        d = bp->b_addr;

        /*
         * ID of the first dquot in the block - id's are zero based.
         */
        curid = id - (id % q->qi_dqperchunk);
        ASSERT(curid >= 0);
        memset(d, 0, BBTOB(q->qi_dqchunklen));
        for (i = 0; i < q->qi_dqperchunk; i++, d++, curid++) {
                d->dd_diskdq.d_magic = cpu_to_be16(XFS_DQUOT_MAGIC);
                d->dd_diskdq.d_version = XFS_DQUOT_VERSION;
                d->dd_diskdq.d_id = cpu_to_be32(curid);
                d->dd_diskdq.d_flags = type;
        }

        xfs_trans_dquot_buf(tp, bp,
                            (type & XFS_DQ_USER ? XFS_BLF_UDQUOT_BUF :
                            ((type & XFS_DQ_PROJ) ? XFS_BLF_PDQUOT_BUF :
                             XFS_BLF_GDQUOT_BUF)));
        xfs_trans_log_buf(tp, bp, 0, BBTOB(q->qi_dqchunklen) - 1);
}



/*
 * Allocate a block and fill it with dquots.
 * This is called when the bmapi finds a hole.
 */
STATIC int
xfs_qm_dqalloc(
        xfs_trans_t     **tpp,
        xfs_mount_t     *mp,
        xfs_dquot_t     *dqp,
        xfs_inode_t     *quotip,
        xfs_fileoff_t   offset_fsb,
        xfs_buf_t       **O_bpp)
{
        xfs_fsblock_t   firstblock;
        xfs_bmap_free_t flist;
        xfs_bmbt_irec_t map;
        int             nmaps, error, committed;
        xfs_buf_t       *bp;
        xfs_trans_t     *tp = *tpp;

        ASSERT(tp != NULL);

        trace_xfs_dqalloc(dqp);

        /*
         * Initialize the bmap freelist prior to calling bmapi code.
         */
        xfs_bmap_init(&flist, &firstblock);
        xfs_ilock(quotip, XFS_ILOCK_EXCL);
        /*
         * Return if this type of quotas is turned off while we didn't
         * have an inode lock
         */
        if (XFS_IS_THIS_QUOTA_OFF(dqp)) {
                xfs_iunlock(quotip, XFS_ILOCK_EXCL);
                return (ESRCH);
        }

        xfs_trans_ijoin(tp, quotip, XFS_ILOCK_EXCL);
        nmaps = 1;
        error = xfs_bmapi_write(tp, quotip, offset_fsb,
                                XFS_DQUOT_CLUSTER_SIZE_FSB, XFS_BMAPI_METADATA,
                                &firstblock, XFS_QM_DQALLOC_SPACE_RES(mp),
                                &map, &nmaps, &flist);
        if (error)
                goto error0;
        ASSERT(map.br_blockcount == XFS_DQUOT_CLUSTER_SIZE_FSB);
        ASSERT(nmaps == 1);
        ASSERT((map.br_startblock != DELAYSTARTBLOCK) &&
               (map.br_startblock != HOLESTARTBLOCK));

        /*
         * Keep track of the blkno to save a lookup later
         */
        dqp->q_blkno = XFS_FSB_TO_DADDR(mp, map.br_startblock);

        /* now we can just get the buffer (there's nothing to read yet) */
        bp = xfs_trans_get_buf(tp, mp->m_ddev_targp,
                               dqp->q_blkno,
                               mp->m_quotainfo->qi_dqchunklen,
                               0);

        error = xfs_buf_geterror(bp);
        if (error)
                goto error1;

        /*
         * Make a chunk of dquots out of this buffer and log
         * the entire thing.
         */
        xfs_qm_init_dquot_blk(tp, mp, be32_to_cpu(dqp->q_core.d_id),
                              dqp->dq_flags & XFS_DQ_ALLTYPES, bp);

        /*
         * xfs_bmap_finish() may commit the current transaction and
         * start a second transaction if the freelist is not empty.
         *
         * Since we still want to modify this buffer, we need to
         * ensure that the buffer is not released on commit of
         * the first transaction and ensure the buffer is added to the
         * second transaction.
         *
         * If there is only one transaction then don't stop the buffer
         * from being released when it commits later on.
         */

        xfs_trans_bhold(tp, bp);

        if ((error = xfs_bmap_finish(tpp, &flist, &committed))) {
                goto error1;
        }

        if (committed) {
                tp = *tpp;
                xfs_trans_bjoin(tp, bp);
        } else {
                xfs_trans_bhold_release(tp, bp);
        }

        *O_bpp = bp;
        return 0;

      error1:
        xfs_bmap_cancel(&flist);
      error0:
        xfs_iunlock(quotip, XFS_ILOCK_EXCL);

        return (error);
}

/*
 * Maps a dquot to the buffer containing its on-disk version.
 * This returns a ptr to the buffer containing the on-disk dquot
 * in the bpp param, and a ptr to the on-disk dquot within that buffer
 */
STATIC int
xfs_qm_dqtobp(
        xfs_trans_t             **tpp,
        xfs_dquot_t             *dqp,
        xfs_disk_dquot_t        **O_ddpp,
        xfs_buf_t               **O_bpp,
        uint                    flags)
{
        xfs_bmbt_irec_t map;
        int             nmaps = 1, error;
        xfs_buf_t       *bp;
        xfs_inode_t     *quotip = XFS_DQ_TO_QIP(dqp);
        xfs_mount_t     *mp = dqp->q_mount;
        xfs_disk_dquot_t *ddq;
        xfs_dqid_t      id = be32_to_cpu(dqp->q_core.d_id);
        xfs_trans_t     *tp = (tpp ? *tpp : NULL);

        dqp->q_fileoffset = (xfs_fileoff_t)id / mp->m_quotainfo->qi_dqperchunk;

        xfs_ilock(quotip, XFS_ILOCK_SHARED);
        if (XFS_IS_THIS_QUOTA_OFF(dqp)) {
                /*
                 * Return if this type of quotas is turned off while we
                 * didn't have the quota inode lock.
                 */
                xfs_iunlock(quotip, XFS_ILOCK_SHARED);
                return ESRCH;
        }

        /*
         * Find the block map; no allocations yet
         */
        error = xfs_bmapi_read(quotip, dqp->q_fileoffset,
                               XFS_DQUOT_CLUSTER_SIZE_FSB, &map, &nmaps, 0);

        xfs_iunlock(quotip, XFS_ILOCK_SHARED);
        if (error)
                return error;

        ASSERT(nmaps == 1);
        ASSERT(map.br_blockcount == 1);

        /*
         * Offset of dquot in the (fixed sized) dquot chunk.
         */
        dqp->q_bufoffset = (id % mp->m_quotainfo->qi_dqperchunk) *
                sizeof(xfs_dqblk_t);

        ASSERT(map.br_startblock != DELAYSTARTBLOCK);
        if (map.br_startblock == HOLESTARTBLOCK) {
                /*
                 * We don't allocate unless we're asked to
                 */
                if (!(flags & XFS_QMOPT_DQALLOC))
                        return ENOENT;

                ASSERT(tp);
                error = xfs_qm_dqalloc(tpp, mp, dqp, quotip,
                                        dqp->q_fileoffset, &bp);
                if (error)
                        return error;
                tp = *tpp;
        } else {
                trace_xfs_dqtobp_read(dqp);

                /*
                 * store the blkno etc so that we don't have to do the
                 * mapping all the time
                 */
                dqp->q_blkno = XFS_FSB_TO_DADDR(mp, map.br_startblock);

                error = xfs_trans_read_buf(mp, tp, mp->m_ddev_targp,
                                           dqp->q_blkno,
                                           mp->m_quotainfo->qi_dqchunklen,
                                           0, &bp);
                if (error || !bp)
                        return XFS_ERROR(error);
        }

        ASSERT(xfs_buf_islocked(bp));

        /*
         * calculate the location of the dquot inside the buffer.
         */
        ddq = bp->b_addr + dqp->q_bufoffset;

        /*
         * A simple sanity check in case we got a corrupted dquot...
         */
        error = xfs_qm_dqcheck(mp, ddq, id, dqp->dq_flags & XFS_DQ_ALLTYPES,
                           flags & (XFS_QMOPT_DQREPAIR|XFS_QMOPT_DOWARN),
                           "dqtobp");
        if (error) {
                if (!(flags & XFS_QMOPT_DQREPAIR)) {
                        xfs_trans_brelse(tp, bp);
                        return XFS_ERROR(EIO);
                }
        }

        *O_bpp = bp;
        *O_ddpp = ddq;

        return (0);
}


/*
 * Read in the ondisk dquot using dqtobp() then copy it to an incore version,
 * and release the buffer immediately.
 *
 * If XFS_QMOPT_DQALLOC is set, allocate a dquot on disk if it needed.
 */
int
xfs_qm_dqread(
        struct xfs_mount        *mp,
        xfs_dqid_t              id,
        uint                    type,
        uint                    flags,
        struct xfs_dquot        **O_dqpp)
{
        struct xfs_dquot        *dqp;
        struct xfs_disk_dquot   *ddqp;
        struct xfs_buf          *bp;
        struct xfs_trans        *tp = NULL;
        int                     error;
        int                     cancelflags = 0;


        dqp = kmem_zone_zalloc(xfs_Gqm->qm_dqzone, KM_SLEEP);

        dqp->dq_flags = type;
        dqp->q_core.d_id = cpu_to_be32(id);
        dqp->q_mount = mp;
        INIT_LIST_HEAD(&dqp->q_freelist);
        mutex_init(&dqp->q_qlock);
        init_waitqueue_head(&dqp->q_pinwait);

        /*
         * Because we want to use a counting completion, complete
         * the flush completion once to allow a single access to
         * the flush completion without blocking.
         */
        init_completion(&dqp->q_flush);
        complete(&dqp->q_flush);

        /*
         * Make sure group quotas have a different lock class than user
         * quotas.
         */
        if (!(type & XFS_DQ_USER))
                lockdep_set_class(&dqp->q_qlock, &xfs_dquot_other_class);

        atomic_inc(&xfs_Gqm->qm_totaldquots);

        trace_xfs_dqread(dqp);

        if (flags & XFS_QMOPT_DQALLOC) {
                tp = xfs_trans_alloc(mp, XFS_TRANS_QM_DQALLOC);
                error = xfs_trans_reserve(tp, XFS_QM_DQALLOC_SPACE_RES(mp),
                                XFS_WRITE_LOG_RES(mp) +
                                /*
                                 * Round the chunklen up to the next multiple
                                 * of 128 (buf log item chunk size)).
                                 */
                                BBTOB(mp->m_quotainfo->qi_dqchunklen) - 1 + 128,
                                0,
                                XFS_TRANS_PERM_LOG_RES,
                                XFS_WRITE_LOG_COUNT);
                if (error)
                        goto error1;
                cancelflags = XFS_TRANS_RELEASE_LOG_RES;
        }

        /*
         * get a pointer to the on-disk dquot and the buffer containing it
         * dqp already knows its own type (GROUP/USER).
         */
        error = xfs_qm_dqtobp(&tp, dqp, &ddqp, &bp, flags);
        if (error) {
                /*
                 * This can happen if quotas got turned off (ESRCH),
                 * or if the dquot didn't exist on disk and we ask to
                 * allocate (ENOENT).
                 */
                trace_xfs_dqread_fail(dqp);
                cancelflags |= XFS_TRANS_ABORT;
                goto error1;
        }

        /* copy everything from disk dquot to the incore dquot */
        memcpy(&dqp->q_core, ddqp, sizeof(xfs_disk_dquot_t));
        xfs_qm_dquot_logitem_init(dqp);

        /*
         * Reservation counters are defined as reservation plus current usage
         * to avoid having to add every time.
         */
        dqp->q_res_bcount = be64_to_cpu(ddqp->d_bcount);
        dqp->q_res_icount = be64_to_cpu(ddqp->d_icount);
        dqp->q_res_rtbcount = be64_to_cpu(ddqp->d_rtbcount);

        /* Mark the buf so that this will stay incore a little longer */
        xfs_buf_set_ref(bp, XFS_DQUOT_REF);

        /*
         * We got the buffer with a xfs_trans_read_buf() (in dqtobp())
         * So we need to release with xfs_trans_brelse().
         * The strategy here is identical to that of inodes; we lock
         * the dquot in xfs_qm_dqget() before making it accessible to
         * others. This is because dquots, like inodes, need a good level of
         * concurrency, and we don't want to take locks on the entire buffers
         * for dquot accesses.
         * Note also that the dquot buffer may even be dirty at this point, if
         * this particular dquot was repaired. We still aren't afraid to
         * brelse it because we have the changes incore.
         */
        ASSERT(xfs_buf_islocked(bp));
        xfs_trans_brelse(tp, bp);

        if (tp) {
                error = xfs_trans_commit(tp, XFS_TRANS_RELEASE_LOG_RES);
                if (error)
                        goto error0;
        }

        *O_dqpp = dqp;
        return error;

error1:
        if (tp)
                xfs_trans_cancel(tp, cancelflags);
error0:
        xfs_qm_dqdestroy(dqp);
        *O_dqpp = NULL;
        return error;
}

/*
 * Lookup a dquot in the incore dquot hashtable. We keep two separate
 * hashtables for user and group dquots; and, these are global tables
 * inside the XQM, not per-filesystem tables.
 * The hash chain must be locked by caller, and it is left locked
 * on return. Returning dquot is locked.
 */
STATIC int
xfs_qm_dqlookup(
        xfs_mount_t             *mp,
        xfs_dqid_t              id,
        xfs_dqhash_t            *qh,
        xfs_dquot_t             **O_dqpp)
{
        xfs_dquot_t             *dqp;

        ASSERT(mutex_is_locked(&qh->qh_lock));

        /*
         * Traverse the hashchain looking for a match
         */
        list_for_each_entry(dqp, &qh->qh_list, q_hashlist) {
                /*
                 * We already have the hashlock. We don't need the
                 * dqlock to look at the id field of the dquot, since the
                 * id can't be modified without the hashlock anyway.
                 */
                if (be32_to_cpu(dqp->q_core.d_id) != id || dqp->q_mount != mp)
                        continue;

                trace_xfs_dqlookup_found(dqp);

                xfs_dqlock(dqp);
                if (dqp->dq_flags & XFS_DQ_FREEING) {
                        *O_dqpp = NULL;
                        xfs_dqunlock(dqp);
                        return -1;
                }

                dqp->q_nrefs++;

                /*
                 * move the dquot to the front of the hashchain
                 */
                list_move(&dqp->q_hashlist, &qh->qh_list);
                trace_xfs_dqlookup_done(dqp);
                *O_dqpp = dqp;
                return 0;
        }

        *O_dqpp = NULL;
        return 1;
}

/*
 * Given the file system, inode OR id, and type (UDQUOT/GDQUOT), return a
 * a locked dquot, doing an allocation (if requested) as needed.
 * When both an inode and an id are given, the inode's id takes precedence.
 * That is, if the id changes while we don't hold the ilock inside this
 * function, the new dquot is returned, not necessarily the one requested
 * in the id argument.
 */
int
xfs_qm_dqget(
        xfs_mount_t     *mp,
        xfs_inode_t     *ip,      /* locked inode (optional) */
        xfs_dqid_t      id,       /* uid/projid/gid depending on type */
        uint            type,     /* XFS_DQ_USER/XFS_DQ_PROJ/XFS_DQ_GROUP */
        uint            flags,    /* DQALLOC, DQSUSER, DQREPAIR, DOWARN */
        xfs_dquot_t     **O_dqpp) /* OUT : locked incore dquot */
{
        xfs_dquot_t     *dqp;
        xfs_dqhash_t    *h;
        uint            version;
        int             error;

        ASSERT(XFS_IS_QUOTA_RUNNING(mp));
        if ((! XFS_IS_UQUOTA_ON(mp) && type == XFS_DQ_USER) ||
            (! XFS_IS_PQUOTA_ON(mp) && type == XFS_DQ_PROJ) ||
            (! XFS_IS_GQUOTA_ON(mp) && type == XFS_DQ_GROUP)) {
                return (ESRCH);
        }
        h = XFS_DQ_HASH(mp, id, type);

#ifdef DEBUG
        if (xfs_do_dqerror) {
                if ((xfs_dqerror_target == mp->m_ddev_targp) &&
                    (xfs_dqreq_num++ % xfs_dqerror_mod) == 0) {
                        xfs_debug(mp, "Returning error in dqget");
                        return (EIO);
                }
        }

        ASSERT(type == XFS_DQ_USER ||
               type == XFS_DQ_PROJ ||
               type == XFS_DQ_GROUP);
        if (ip) {
                ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
                if (type == XFS_DQ_USER)
                        ASSERT(ip->i_udquot == NULL);
                else
                        ASSERT(ip->i_gdquot == NULL);
        }
#endif

restart:
        mutex_lock(&h->qh_lock);

        /*
         * Look in the cache (hashtable).
         * The chain is kept locked during lookup.
         */
        switch (xfs_qm_dqlookup(mp, id, h, O_dqpp)) {
        case -1:
                XQM_STATS_INC(xqmstats.xs_qm_dquot_dups);
                mutex_unlock(&h->qh_lock);
                delay(1);
                goto restart;
        case 0:
                XQM_STATS_INC(xqmstats.xs_qm_dqcachehits);
                /*
                 * The dquot was found, moved to the front of the chain,
                 * taken off the freelist if it was on it, and locked
                 * at this point. Just unlock the hashchain and return.
                 */
                ASSERT(*O_dqpp);
                ASSERT(XFS_DQ_IS_LOCKED(*O_dqpp));
                mutex_unlock(&h->qh_lock);
                trace_xfs_dqget_hit(*O_dqpp);
                return 0;       /* success */
        default:
                XQM_STATS_INC(xqmstats.xs_qm_dqcachemisses);
                break;
        }

        /*
         * Dquot cache miss. We don't want to keep the inode lock across
         * a (potential) disk read. Also we don't want to deal with the lock
         * ordering between quotainode and this inode. OTOH, dropping the inode
         * lock here means dealing with a chown that can happen before
         * we re-acquire the lock.
         */
        if (ip)
                xfs_iunlock(ip, XFS_ILOCK_EXCL);
        /*
         * Save the hashchain version stamp, and unlock the chain, so that
         * we don't keep the lock across a disk read
         */
        version = h->qh_version;
        mutex_unlock(&h->qh_lock);

        error = xfs_qm_dqread(mp, id, type, flags, &dqp);

        if (ip)
                xfs_ilock(ip, XFS_ILOCK_EXCL);

        if (error)
                return error;

        /*
         * Dquot lock comes after hashlock in the lock ordering
         */
        if (ip) {
                /*
                 * A dquot could be attached to this inode by now, since
                 * we had dropped the ilock.
                 */
                if (type == XFS_DQ_USER) {
                        if (!XFS_IS_UQUOTA_ON(mp)) {
                                /* inode stays locked on return */
                                xfs_qm_dqdestroy(dqp);
                                return XFS_ERROR(ESRCH);
                        }
                        if (ip->i_udquot) {
                                xfs_qm_dqdestroy(dqp);
                                dqp = ip->i_udquot;
                                xfs_dqlock(dqp);
                                goto dqret;
                        }
                } else {
                        if (!XFS_IS_OQUOTA_ON(mp)) {
                                /* inode stays locked on return */
                                xfs_qm_dqdestroy(dqp);
                                return XFS_ERROR(ESRCH);
                        }
                        if (ip->i_gdquot) {
                                xfs_qm_dqdestroy(dqp);
                                dqp = ip->i_gdquot;
                                xfs_dqlock(dqp);
                                goto dqret;
                        }
                }
        }

        /*
         * Hashlock comes after ilock in lock order
         */
        mutex_lock(&h->qh_lock);
        if (version != h->qh_version) {
                xfs_dquot_t *tmpdqp;
                /*
                 * Now, see if somebody else put the dquot in the
                 * hashtable before us. This can happen because we didn't
                 * keep the hashchain lock. We don't have to worry about
                 * lock order between the two dquots here since dqp isn't
                 * on any findable lists yet.
                 */
                switch (xfs_qm_dqlookup(mp, id, h, &tmpdqp)) {
                case 0:
                case -1:
                        /*
                         * Duplicate found, either in cache or on its way out.
                         * Just throw away the new dquot and start over.
                         */
                        if (tmpdqp)
                                xfs_qm_dqput(tmpdqp);
                        mutex_unlock(&h->qh_lock);
                        xfs_qm_dqdestroy(dqp);
                        XQM_STATS_INC(xqmstats.xs_qm_dquot_dups);
                        goto restart;
                default:
                        break;
                }
        }

        /*
         * Put the dquot at the beginning of the hash-chain and mp's list
         * LOCK ORDER: hashlock, freelistlock, mplistlock, udqlock, gdqlock ..
         */
        ASSERT(mutex_is_locked(&h->qh_lock));
        dqp->q_hash = h;
        list_add(&dqp->q_hashlist, &h->qh_list);
        h->qh_version++;

        /*
         * Attach this dquot to this filesystem's list of all dquots,
         * kept inside the mount structure in m_quotainfo field
         */
        mutex_lock(&mp->m_quotainfo->qi_dqlist_lock);

        /*
         * We return a locked dquot to the caller, with a reference taken
         */
        xfs_dqlock(dqp);
        dqp->q_nrefs = 1;

        list_add(&dqp->q_mplist, &mp->m_quotainfo->qi_dqlist);
        mp->m_quotainfo->qi_dquots++;
        mutex_unlock(&mp->m_quotainfo->qi_dqlist_lock);
        mutex_unlock(&h->qh_lock);
 dqret:
        ASSERT((ip == NULL) || xfs_isilocked(ip, XFS_ILOCK_EXCL));
        trace_xfs_dqget_miss(dqp);
        *O_dqpp = dqp;
        return (0);
}


/*
 * Release a reference to the dquot (decrement ref-count)
 * and unlock it. If there is a group quota attached to this
 * dquot, carefully release that too without tripping over
 * deadlocks'n'stuff.
 */
void
xfs_qm_dqput(
        struct xfs_dquot        *dqp)
{
        struct xfs_dquot        *gdqp;

        ASSERT(dqp->q_nrefs > 0);
        ASSERT(XFS_DQ_IS_LOCKED(dqp));

        trace_xfs_dqput(dqp);

recurse:
        if (--dqp->q_nrefs > 0) {
                xfs_dqunlock(dqp);
                return;
        }

        trace_xfs_dqput_free(dqp);

        mutex_lock(&xfs_Gqm->qm_dqfrlist_lock);
        if (list_empty(&dqp->q_freelist)) {
                list_add_tail(&dqp->q_freelist, &xfs_Gqm->qm_dqfrlist);
                xfs_Gqm->qm_dqfrlist_cnt++;
        }
        mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);

        /*
         * If we just added a udquot to the freelist, then we want to release
         * the gdquot reference that it (probably) has. Otherwise it'll keep
         * the gdquot from getting reclaimed.
         */
        gdqp = dqp->q_gdquot;
        if (gdqp) {
                xfs_dqlock(gdqp);
                dqp->q_gdquot = NULL;
        }
        xfs_dqunlock(dqp);

        /*
         * If we had a group quota hint, release it now.
         */
        if (gdqp) {
                dqp = gdqp;
                goto recurse;
        }
}

/*
 * Release a dquot. Flush it if dirty, then dqput() it.
 * dquot must not be locked.
 */
void
xfs_qm_dqrele(
        xfs_dquot_t     *dqp)
{
        if (!dqp)
                return;

        trace_xfs_dqrele(dqp);

        xfs_dqlock(dqp);
        /*
         * We don't care to flush it if the dquot is dirty here.
         * That will create stutters that we want to avoid.
         * Instead we do a delayed write when we try to reclaim
         * a dirty dquot. Also xfs_sync will take part of the burden...
         */
        xfs_qm_dqput(dqp);
}

/*
 * This is the dquot flushing I/O completion routine.  It is called
 * from interrupt level when the buffer containing the dquot is
 * flushed to disk.  It is responsible for removing the dquot logitem
 * from the AIL if it has not been re-logged, and unlocking the dquot's
 * flush lock. This behavior is very similar to that of inodes..
 */
STATIC void
xfs_qm_dqflush_done(
        struct xfs_buf          *bp,
        struct xfs_log_item     *lip)
{
        xfs_dq_logitem_t        *qip = (struct xfs_dq_logitem *)lip;
        xfs_dquot_t             *dqp = qip->qli_dquot;
        struct xfs_ail          *ailp = lip->li_ailp;

        /*
         * We only want to pull the item from the AIL if its
         * location in the log has not changed since we started the flush.
         * Thus, we only bother if the dquot's lsn has
         * not changed. First we check the lsn outside the lock
         * since it's cheaper, and then we recheck while
         * holding the lock before removing the dquot from the AIL.
         */
        if ((lip->li_flags & XFS_LI_IN_AIL) &&
            lip->li_lsn == qip->qli_flush_lsn) {

                /* xfs_trans_ail_delete() drops the AIL lock. */
                spin_lock(&ailp->xa_lock);
                if (lip->li_lsn == qip->qli_flush_lsn)
                        xfs_trans_ail_delete(ailp, lip);
                else
                        spin_unlock(&ailp->xa_lock);
        }

        /*
         * Release the dq's flush lock since we're done with it.
         */
        xfs_dqfunlock(dqp);
}

/*
 * Write a modified dquot to disk.
 * The dquot must be locked and the flush lock too taken by caller.
 * The flush lock will not be unlocked until the dquot reaches the disk,
 * but the dquot is free to be unlocked and modified by the caller
 * in the interim. Dquot is still locked on return. This behavior is
 * identical to that of inodes.
 */
int
xfs_qm_dqflush(
        xfs_dquot_t             *dqp,
        uint                    flags)
{
        struct xfs_mount        *mp = dqp->q_mount;
        struct xfs_buf          *bp;
        struct xfs_disk_dquot   *ddqp;
        int                     error;

        ASSERT(XFS_DQ_IS_LOCKED(dqp));
        ASSERT(!completion_done(&dqp->q_flush));

        trace_xfs_dqflush(dqp);

        /*
         * If not dirty, or it's pinned and we are not supposed to block, nada.
         */
        if (!XFS_DQ_IS_DIRTY(dqp) ||
            ((flags & SYNC_TRYLOCK) && atomic_read(&dqp->q_pincount) > 0)) {
                xfs_dqfunlock(dqp);
                return 0;
        }
        xfs_qm_dqunpin_wait(dqp);

        /*
         * This may have been unpinned because the filesystem is shutting
         * down forcibly. If that's the case we must not write this dquot
         * to disk, because the log record didn't make it to disk!
         */
        if (XFS_FORCED_SHUTDOWN(mp)) {
                dqp->dq_flags &= ~XFS_DQ_DIRTY;
                xfs_dqfunlock(dqp);
                return XFS_ERROR(EIO);
        }

        /*
         * Get the buffer containing the on-disk dquot
         */
        error = xfs_trans_read_buf(mp, NULL, mp->m_ddev_targp, dqp->q_blkno,
                                   mp->m_quotainfo->qi_dqchunklen, 0, &bp);
        if (error) {
                ASSERT(error != ENOENT);
                xfs_dqfunlock(dqp);
                return error;
        }

        /*
         * Calculate the location of the dquot inside the buffer.
         */
        ddqp = bp->b_addr + dqp->q_bufoffset;

        /*
         * A simple sanity check in case we got a corrupted dquot..
         */
        error = xfs_qm_dqcheck(mp, &dqp->q_core, be32_to_cpu(ddqp->d_id), 0,
                           XFS_QMOPT_DOWARN, "dqflush (incore copy)");
        if (error) {
                xfs_buf_relse(bp);
                xfs_dqfunlock(dqp);
                xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
                return XFS_ERROR(EIO);
        }

        /* This is the only portion of data that needs to persist */
        memcpy(ddqp, &dqp->q_core, sizeof(xfs_disk_dquot_t));

        /*
         * Clear the dirty field and remember the flush lsn for later use.
         */
        dqp->dq_flags &= ~XFS_DQ_DIRTY;

        xfs_trans_ail_copy_lsn(mp->m_ail, &dqp->q_logitem.qli_flush_lsn,
                                        &dqp->q_logitem.qli_item.li_lsn);

        /*
         * Attach an iodone routine so that we can remove this dquot from the
         * AIL and release the flush lock once the dquot is synced to disk.
         */
        xfs_buf_attach_iodone(bp, xfs_qm_dqflush_done,
                                  &dqp->q_logitem.qli_item);

        /*
         * If the buffer is pinned then push on the log so we won't
         * get stuck waiting in the write for too long.
         */
        if (xfs_buf_ispinned(bp)) {
                trace_xfs_dqflush_force(dqp);
                xfs_log_force(mp, 0);
        }

        if (flags & SYNC_WAIT)
                error = xfs_bwrite(bp);
        else
                xfs_buf_delwri_queue(bp);

        xfs_buf_relse(bp);

        trace_xfs_dqflush_done(dqp);

        /*
         * dqp is still locked, but caller is free to unlock it now.
         */
        return error;

}

void
xfs_dqunlock(
        xfs_dquot_t *dqp)
{
        xfs_dqunlock_nonotify(dqp);
        if (dqp->q_logitem.qli_dquot == dqp) {
                xfs_trans_unlocked_item(dqp->q_logitem.qli_item.li_ailp,
                                        &dqp->q_logitem.qli_item);
        }
}

/*
 * Lock two xfs_dquot structures.
 *
 * To avoid deadlocks we always lock the quota structure with
 * the lowerd id first.
 */
void
xfs_dqlock2(
        xfs_dquot_t     *d1,
        xfs_dquot_t     *d2)
{
        if (d1 && d2) {
                ASSERT(d1 != d2);
                if (be32_to_cpu(d1->q_core.d_id) >
                    be32_to_cpu(d2->q_core.d_id)) {
                        mutex_lock(&d2->q_qlock);
                        mutex_lock_nested(&d1->q_qlock, XFS_QLOCK_NESTED);
                } else {
                        mutex_lock(&d1->q_qlock);
                        mutex_lock_nested(&d2->q_qlock, XFS_QLOCK_NESTED);
                }
        } else if (d1) {
                mutex_lock(&d1->q_qlock);
        } else if (d2) {
                mutex_lock(&d2->q_qlock);
        }
}

/*
 * Take a dquot out of the mount's dqlist as well as the hashlist.  This is
 * called via unmount as well as quotaoff, and the purge will always succeed.
 */
void
xfs_qm_dqpurge(
        struct xfs_dquot        *dqp)
{
        struct xfs_mount        *mp = dqp->q_mount;
        struct xfs_dqhash       *qh = dqp->q_hash;

        xfs_dqlock(dqp);

        /*
         * If we're turning off quotas, we have to make sure that, for
         * example, we don't delete quota disk blocks while dquots are
         * in the process of getting written to those disk blocks.
         * This dquot might well be on AIL, and we can't leave it there
         * if we're turning off quotas. Basically, we need this flush
         * lock, and are willing to block on it.
         */
        if (!xfs_dqflock_nowait(dqp)) {
                /*
                 * Block on the flush lock after nudging dquot buffer,
                 * if it is incore.
                 */
                xfs_dqflock_pushbuf_wait(dqp);
        }

        /*
         * If we are turning this type of quotas off, we don't care
         * about the dirty metadata sitting in this dquot. OTOH, if
         * we're unmounting, we do care, so we flush it and wait.
         */
        if (XFS_DQ_IS_DIRTY(dqp)) {
                int     error;

                /*
                 * We don't care about getting disk errors here. We need
                 * to purge this dquot anyway, so we go ahead regardless.
                 */
                error = xfs_qm_dqflush(dqp, SYNC_WAIT);
                if (error)
                        xfs_warn(mp, "%s: dquot %p flush failed",
                                __func__, dqp);
                xfs_dqflock(dqp);
        }

        ASSERT(atomic_read(&dqp->q_pincount) == 0);
        ASSERT(XFS_FORCED_SHUTDOWN(mp) ||
               !(dqp->q_logitem.qli_item.li_flags & XFS_LI_IN_AIL));

        xfs_dqfunlock(dqp);
        xfs_dqunlock(dqp);

        mutex_lock(&qh->qh_lock);
        list_del_init(&dqp->q_hashlist);
        qh->qh_version++;
        mutex_unlock(&qh->qh_lock);

        mutex_lock(&mp->m_quotainfo->qi_dqlist_lock);
        list_del_init(&dqp->q_mplist);
        mp->m_quotainfo->qi_dqreclaims++;
        mp->m_quotainfo->qi_dquots--;
        mutex_unlock(&mp->m_quotainfo->qi_dqlist_lock);

        /*
         * We move dquots to the freelist as soon as their reference count
         * hits zero, so it really should be on the freelist here.
         */
        mutex_lock(&xfs_Gqm->qm_dqfrlist_lock);
        ASSERT(!list_empty(&dqp->q_freelist));
        list_del_init(&dqp->q_freelist);
        xfs_Gqm->qm_dqfrlist_cnt--;
        mutex_unlock(&xfs_Gqm->qm_dqfrlist_lock);

        xfs_qm_dqdestroy(dqp);
}

/*
 * Give the buffer a little push if it is incore and
 * wait on the flush lock.
 */
void
xfs_dqflock_pushbuf_wait(
        xfs_dquot_t     *dqp)
{
        xfs_mount_t     *mp = dqp->q_mount;
        xfs_buf_t       *bp;

        /*
         * Check to see if the dquot has been flushed delayed
         * write.  If so, grab its buffer and send it
         * out immediately.  We'll be able to acquire
         * the flush lock when the I/O completes.
         */
        bp = xfs_incore(mp->m_ddev_targp, dqp->q_blkno,
                        mp->m_quotainfo->qi_dqchunklen, XBF_TRYLOCK);
        if (!bp)
                goto out_lock;

        if (XFS_BUF_ISDELAYWRITE(bp)) {
                if (xfs_buf_ispinned(bp))
                        xfs_log_force(mp, 0);
                xfs_buf_delwri_promote(bp);
                wake_up_process(bp->b_target->bt_task);
        }
        xfs_buf_relse(bp);
out_lock:
        xfs_dqflock(dqp);
}