xfs_log_cil.c

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/*
 * Copyright (c) 2010 Red Hat, 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_log.h"
#include "xfs_trans.h"
#include "xfs_trans_priv.h"
#include "xfs_log_priv.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_mount.h"
#include "xfs_error.h"
#include "xfs_alloc.h"
#include "xfs_extent_busy.h"
#include "xfs_discard.h"

/*
 * Allocate a new ticket. Failing to get a new ticket makes it really hard to
 * recover, so we don't allow failure here. Also, we allocate in a context that
 * we don't want to be issuing transactions from, so we need to tell the
 * allocation code this as well.
 *
 * We don't reserve any space for the ticket - we are going to steal whatever
 * space we require from transactions as they commit. To ensure we reserve all
 * the space required, we need to set the current reservation of the ticket to
 * zero so that we know to steal the initial transaction overhead from the
 * first transaction commit.
 */
static struct xlog_ticket *
xlog_cil_ticket_alloc(
    struct xlog *log)
{
    struct xlog_ticket *tic;

    tic = xlog_ticket_alloc(log, 0, 1, XFS_TRANSACTION, 0,
                KM_SLEEP|KM_NOFS);
    tic->t_trans_type = XFS_TRANS_CHECKPOINT;

    /*
     * set the current reservation to zero so we know to steal the basic
     * transaction overhead reservation from the first transaction commit.
     */
    tic->t_curr_res = 0;
    return tic;
}

/*
 * After the first stage of log recovery is done, we know where the head and
 * tail of the log are. We need this log initialisation done before we can
 * initialise the first CIL checkpoint context.
 *
 * Here we allocate a log ticket to track space usage during a CIL push.  This
 * ticket is passed to xlog_write() directly so that we don't slowly leak log
 * space by failing to account for space used by log headers and additional
 * region headers for split regions.
 */
void
xlog_cil_init_post_recovery(
    struct xlog *log)
{
    log->l_cilp->xc_ctx->ticket = xlog_cil_ticket_alloc(log);
    log->l_cilp->xc_ctx->sequence = 1;
    log->l_cilp->xc_ctx->commit_lsn = xlog_assign_lsn(log->l_curr_cycle,
                                log->l_curr_block);
}

/*
 * Format log item into a flat buffers
 *
 * For delayed logging, we need to hold a formatted buffer containing all the
 * changes on the log item. This enables us to relog the item in memory and
 * write it out asynchronously without needing to relock the object that was
 * modified at the time it gets written into the iclog.
 *
 * This function builds a vector for the changes in each log item in the
 * transaction. It then works out the length of the buffer needed for each log
 * item, allocates them and formats the vector for the item into the buffer.
 * The buffer is then attached to the log item are then inserted into the
 * Committed Item List for tracking until the next checkpoint is written out.
 *
 * We don't set up region headers during this process; we simply copy the
 * regions into the flat buffer. We can do this because we still have to do a
 * formatting step to write the regions into the iclog buffer.  Writing the
 * ophdrs during the iclog write means that we can support splitting large
 * regions across iclog boundares without needing a change in the format of the
 * item/region encapsulation.
 *
 * Hence what we need to do now is change the rewrite the vector array to point
 * to the copied region inside the buffer we just allocated. This allows us to
 * format the regions into the iclog as though they are being formatted
 * directly out of the objects themselves.
 */
static struct xfs_log_vec *
xlog_cil_prepare_log_vecs(
    struct xfs_trans    *tp)
{
    struct xfs_log_item_desc *lidp;
    struct xfs_log_vec  *lv = NULL;
    struct xfs_log_vec  *ret_lv = NULL;


    /* Bail out if we didn't find a log item.  */
    if (list_empty(&tp->t_items)) {
        ASSERT(0);
        return NULL;
    }

    list_for_each_entry(lidp, &tp->t_items, lid_trans) {
        struct xfs_log_vec *new_lv;
        void    *ptr;
        int index;
        int len = 0;
        uint    niovecs;

        /* Skip items which aren't dirty in this transaction. */
        if (!(lidp->lid_flags & XFS_LID_DIRTY))
            continue;

        /* Skip items that do not have any vectors for writing */
        niovecs = IOP_SIZE(lidp->lid_item);
        if (!niovecs)
            continue;

        new_lv = kmem_zalloc(sizeof(*new_lv) +
                niovecs * sizeof(struct xfs_log_iovec),
                KM_SLEEP);

        /* The allocated iovec region lies beyond the log vector. */
        new_lv->lv_iovecp = (struct xfs_log_iovec *)&new_lv[1];
        new_lv->lv_niovecs = niovecs;
        new_lv->lv_item = lidp->lid_item;

        /* build the vector array and calculate it's length */
        IOP_FORMAT(new_lv->lv_item, new_lv->lv_iovecp);
        for (index = 0; index < new_lv->lv_niovecs; index++)
            len += new_lv->lv_iovecp[index].i_len;

        new_lv->lv_buf_len = len;
        new_lv->lv_buf = kmem_alloc(new_lv->lv_buf_len,
                KM_SLEEP|KM_NOFS);
        ptr = new_lv->lv_buf;

        for (index = 0; index < new_lv->lv_niovecs; index++) {
            struct xfs_log_iovec *vec = &new_lv->lv_iovecp[index];

            memcpy(ptr, vec->i_addr, vec->i_len);
            vec->i_addr = ptr;
            ptr += vec->i_len;
        }
        ASSERT(ptr == new_lv->lv_buf + new_lv->lv_buf_len);

        if (!ret_lv)
            ret_lv = new_lv;
        else
            lv->lv_next = new_lv;
        lv = new_lv;
    }

    return ret_lv;
}

/*
 * Prepare the log item for insertion into the CIL. Calculate the difference in
 * log space and vectors it will consume, and if it is a new item pin it as
 * well.
 */
STATIC void
xfs_cil_prepare_item(
    struct xlog     *log,
    struct xfs_log_vec  *lv,
    int         *len,
    int         *diff_iovecs)
{
    struct xfs_log_vec  *old = lv->lv_item->li_lv;

    if (old) {
        /* existing lv on log item, space used is a delta */
        ASSERT(!list_empty(&lv->lv_item->li_cil));
        ASSERT(old->lv_buf && old->lv_buf_len && old->lv_niovecs);

        *len += lv->lv_buf_len - old->lv_buf_len;
        *diff_iovecs += lv->lv_niovecs - old->lv_niovecs;
        kmem_free(old->lv_buf);
        kmem_free(old);
    } else {
        /* new lv, must pin the log item */
        ASSERT(!lv->lv_item->li_lv);
        ASSERT(list_empty(&lv->lv_item->li_cil));

        *len += lv->lv_buf_len;
        *diff_iovecs += lv->lv_niovecs;
        IOP_PIN(lv->lv_item);

    }

    /* attach new log vector to log item */
    lv->lv_item->li_lv = lv;

    /*
     * If this is the first time the item is being committed to the
     * CIL, store the sequence number on the log item so we can
     * tell in future commits whether this is the first checkpoint
     * the item is being committed into.
     */
    if (!lv->lv_item->li_seq)
        lv->lv_item->li_seq = log->l_cilp->xc_ctx->sequence;
}

/*
 * Insert the log items into the CIL and calculate the difference in space
 * consumed by the item. Add the space to the checkpoint ticket and calculate
 * if the change requires additional log metadata. If it does, take that space
 * as well. Remove the amount of space we added to the checkpoint ticket from
 * the current transaction ticket so that the accounting works out correctly.
 */
static void
xlog_cil_insert_items(
    struct xlog     *log,
    struct xfs_log_vec  *log_vector,
    struct xlog_ticket  *ticket)
{
    struct xfs_cil      *cil = log->l_cilp;
    struct xfs_cil_ctx  *ctx = cil->xc_ctx;
    struct xfs_log_vec  *lv;
    int         len = 0;
    int         diff_iovecs = 0;
    int         iclog_space;

    ASSERT(log_vector);

    /*
     * Do all the accounting aggregation and switching of log vectors
     * around in a separate loop to the insertion of items into the CIL.
     * Then we can do a separate loop to update the CIL within a single
     * lock/unlock pair. This reduces the number of round trips on the CIL
     * lock from O(nr_logvectors) to O(1) and greatly reduces the overall
     * hold time for the transaction commit.
     *
     * If this is the first time the item is being placed into the CIL in
     * this context, pin it so it can't be written to disk until the CIL is
     * flushed to the iclog and the iclog written to disk.
     *
     * We can do this safely because the context can't checkpoint until we
     * are done so it doesn't matter exactly how we update the CIL.
     */
    for (lv = log_vector; lv; lv = lv->lv_next)
        xfs_cil_prepare_item(log, lv, &len, &diff_iovecs);

    /* account for space used by new iovec headers  */
    len += diff_iovecs * sizeof(xlog_op_header_t);

    spin_lock(&cil->xc_cil_lock);

    /* move the items to the tail of the CIL */
    for (lv = log_vector; lv; lv = lv->lv_next)
        list_move_tail(&lv->lv_item->li_cil, &cil->xc_cil);

    ctx->nvecs += diff_iovecs;

    /*
     * Now transfer enough transaction reservation to the context ticket
     * for the checkpoint. The context ticket is special - the unit
     * reservation has to grow as well as the current reservation as we
     * steal from tickets so we can correctly determine the space used
     * during the transaction commit.
     */
    if (ctx->ticket->t_curr_res == 0) {
        /* first commit in checkpoint, steal the header reservation */
        ASSERT(ticket->t_curr_res >= ctx->ticket->t_unit_res + len);
        ctx->ticket->t_curr_res = ctx->ticket->t_unit_res;
        ticket->t_curr_res -= ctx->ticket->t_unit_res;
    }

    /* do we need space for more log record headers? */
    iclog_space = log->l_iclog_size - log->l_iclog_hsize;
    if (len > 0 && (ctx->space_used / iclog_space !=
                (ctx->space_used + len) / iclog_space)) {
        int hdrs;

        hdrs = (len + iclog_space - 1) / iclog_space;
        /* need to take into account split region headers, too */
        hdrs *= log->l_iclog_hsize + sizeof(struct xlog_op_header);
        ctx->ticket->t_unit_res += hdrs;
        ctx->ticket->t_curr_res += hdrs;
        ticket->t_curr_res -= hdrs;
        ASSERT(ticket->t_curr_res >= len);
    }
    ticket->t_curr_res -= len;
    ctx->space_used += len;

    spin_unlock(&cil->xc_cil_lock);
}

static void
xlog_cil_free_logvec(
    struct xfs_log_vec  *log_vector)
{
    struct xfs_log_vec  *lv;

    for (lv = log_vector; lv; ) {
        struct xfs_log_vec *next = lv->lv_next;
        kmem_free(lv->lv_buf);
        kmem_free(lv);
        lv = next;
    }
}

/*
 * Mark all items committed and clear busy extents. We free the log vector
 * chains in a separate pass so that we unpin the log items as quickly as
 * possible.
 */
static void
xlog_cil_committed(
    void    *args,
    int abort)
{
    struct xfs_cil_ctx  *ctx = args;
    struct xfs_mount    *mp = ctx->cil->xc_log->l_mp;

    xfs_trans_committed_bulk(ctx->cil->xc_log->l_ailp, ctx->lv_chain,
                    ctx->start_lsn, abort);

    xfs_extent_busy_sort(&ctx->busy_extents);
    xfs_extent_busy_clear(mp, &ctx->busy_extents,
                 (mp->m_flags & XFS_MOUNT_DISCARD) && !abort);

    spin_lock(&ctx->cil->xc_cil_lock);
    list_del(&ctx->committing);
    spin_unlock(&ctx->cil->xc_cil_lock);

    xlog_cil_free_logvec(ctx->lv_chain);

    if (!list_empty(&ctx->busy_extents)) {
        ASSERT(mp->m_flags & XFS_MOUNT_DISCARD);

        xfs_discard_extents(mp, &ctx->busy_extents);
        xfs_extent_busy_clear(mp, &ctx->busy_extents, false);
    }

    kmem_free(ctx);
}

/*
 * Push the Committed Item List to the log. If @push_seq flag is zero, then it
 * is a background flush and so we can chose to ignore it. Otherwise, if the
 * current sequence is the same as @push_seq we need to do a flush. If
 * @push_seq is less than the current sequence, then it has already been
 * flushed and we don't need to do anything - the caller will wait for it to
 * complete if necessary.
 *
 * @push_seq is a value rather than a flag because that allows us to do an
 * unlocked check of the sequence number for a match. Hence we can allows log
 * forces to run racily and not issue pushes for the same sequence twice. If we
 * get a race between multiple pushes for the same sequence they will block on
 * the first one and then abort, hence avoiding needless pushes.
 */
STATIC int
xlog_cil_push(
    struct xlog     *log)
{
    struct xfs_cil      *cil = log->l_cilp;
    struct xfs_log_vec  *lv;
    struct xfs_cil_ctx  *ctx;
    struct xfs_cil_ctx  *new_ctx;
    struct xlog_in_core *commit_iclog;
    struct xlog_ticket  *tic;
    int         num_lv;
    int         num_iovecs;
    int         len;
    int         error = 0;
    struct xfs_trans_header thdr;
    struct xfs_log_iovec    lhdr;
    struct xfs_log_vec  lvhdr = { NULL };
    xfs_lsn_t       commit_lsn;
    xfs_lsn_t       push_seq;

    if (!cil)
        return 0;

    new_ctx = kmem_zalloc(sizeof(*new_ctx), KM_SLEEP|KM_NOFS);
    new_ctx->ticket = xlog_cil_ticket_alloc(log);

    down_write(&cil->xc_ctx_lock);
    ctx = cil->xc_ctx;

    spin_lock(&cil->xc_cil_lock);
    push_seq = cil->xc_push_seq;
    ASSERT(push_seq <= ctx->sequence);

    /*
     * Check if we've anything to push. If there is nothing, then we don't
     * move on to a new sequence number and so we have to be able to push
     * this sequence again later.
     */
    if (list_empty(&cil->xc_cil)) {
        cil->xc_push_seq = 0;
        spin_unlock(&cil->xc_cil_lock);
        goto out_skip;
    }
    spin_unlock(&cil->xc_cil_lock);


    /* check for a previously pushed seqeunce */
    if (push_seq < cil->xc_ctx->sequence)
        goto out_skip;

    /*
     * pull all the log vectors off the items in the CIL, and
     * remove the items from the CIL. We don't need the CIL lock
     * here because it's only needed on the transaction commit
     * side which is currently locked out by the flush lock.
     */
    lv = NULL;
    num_lv = 0;
    num_iovecs = 0;
    len = 0;
    while (!list_empty(&cil->xc_cil)) {
        struct xfs_log_item *item;
        int         i;

        item = list_first_entry(&cil->xc_cil,
                    struct xfs_log_item, li_cil);
        list_del_init(&item->li_cil);
        if (!ctx->lv_chain)
            ctx->lv_chain = item->li_lv;
        else
            lv->lv_next = item->li_lv;
        lv = item->li_lv;
        item->li_lv = NULL;

        num_lv++;
        num_iovecs += lv->lv_niovecs;
        for (i = 0; i < lv->lv_niovecs; i++)
            len += lv->lv_iovecp[i].i_len;
    }

    /*
     * initialise the new context and attach it to the CIL. Then attach
     * the current context to the CIL committing lsit so it can be found
     * during log forces to extract the commit lsn of the sequence that
     * needs to be forced.
     */
    INIT_LIST_HEAD(&new_ctx->committing);
    INIT_LIST_HEAD(&new_ctx->busy_extents);
    new_ctx->sequence = ctx->sequence + 1;
    new_ctx->cil = cil;
    cil->xc_ctx = new_ctx;

    /*
     * mirror the new sequence into the cil structure so that we can do
     * unlocked checks against the current sequence in log forces without
     * risking deferencing a freed context pointer.
     */
    cil->xc_current_sequence = new_ctx->sequence;

    /*
     * The switch is now done, so we can drop the context lock and move out
     * of a shared context. We can't just go straight to the commit record,
     * though - we need to synchronise with previous and future commits so
     * that the commit records are correctly ordered in the log to ensure
     * that we process items during log IO completion in the correct order.
     *
     * For example, if we get an EFI in one checkpoint and the EFD in the
     * next (e.g. due to log forces), we do not want the checkpoint with
     * the EFD to be committed before the checkpoint with the EFI.  Hence
     * we must strictly order the commit records of the checkpoints so
     * that: a) the checkpoint callbacks are attached to the iclogs in the
     * correct order; and b) the checkpoints are replayed in correct order
     * in log recovery.
     *
     * Hence we need to add this context to the committing context list so
     * that higher sequences will wait for us to write out a commit record
     * before they do.
     */
    spin_lock(&cil->xc_cil_lock);
    list_add(&ctx->committing, &cil->xc_committing);
    spin_unlock(&cil->xc_cil_lock);
    up_write(&cil->xc_ctx_lock);

    /*
     * Build a checkpoint transaction header and write it to the log to
     * begin the transaction. We need to account for the space used by the
     * transaction header here as it is not accounted for in xlog_write().
     *
     * The LSN we need to pass to the log items on transaction commit is
     * the LSN reported by the first log vector write. If we use the commit
     * record lsn then we can move the tail beyond the grant write head.
     */
    tic = ctx->ticket;
    thdr.th_magic = XFS_TRANS_HEADER_MAGIC;
    thdr.th_type = XFS_TRANS_CHECKPOINT;
    thdr.th_tid = tic->t_tid;
    thdr.th_num_items = num_iovecs;
    lhdr.i_addr = &thdr;
    lhdr.i_len = sizeof(xfs_trans_header_t);
    lhdr.i_type = XLOG_REG_TYPE_TRANSHDR;
    tic->t_curr_res -= lhdr.i_len + sizeof(xlog_op_header_t);

    lvhdr.lv_niovecs = 1;
    lvhdr.lv_iovecp = &lhdr;
    lvhdr.lv_next = ctx->lv_chain;

    error = xlog_write(log, &lvhdr, tic, &ctx->start_lsn, NULL, 0);
    if (error)
        goto out_abort_free_ticket;

    /*
     * now that we've written the checkpoint into the log, strictly
     * order the commit records so replay will get them in the right order.
     */
restart:
    spin_lock(&cil->xc_cil_lock);
    list_for_each_entry(new_ctx, &cil->xc_committing, committing) {
        /*
         * Higher sequences will wait for this one so skip them.
         * Don't wait for own own sequence, either.
         */
        if (new_ctx->sequence >= ctx->sequence)
            continue;
        if (!new_ctx->commit_lsn) {
            /*
             * It is still being pushed! Wait for the push to
             * complete, then start again from the beginning.
             */
            xlog_wait(&cil->xc_commit_wait, &cil->xc_cil_lock);
            goto restart;
        }
    }
    spin_unlock(&cil->xc_cil_lock);

    /* xfs_log_done always frees the ticket on error. */
    commit_lsn = xfs_log_done(log->l_mp, tic, &commit_iclog, 0);
    if (commit_lsn == -1)
        goto out_abort;

    /* attach all the transactions w/ busy extents to iclog */
    ctx->log_cb.cb_func = xlog_cil_committed;
    ctx->log_cb.cb_arg = ctx;
    error = xfs_log_notify(log->l_mp, commit_iclog, &ctx->log_cb);
    if (error)
        goto out_abort;

    /*
     * now the checkpoint commit is complete and we've attached the
     * callbacks to the iclog we can assign the commit LSN to the context
     * and wake up anyone who is waiting for the commit to complete.
     */
    spin_lock(&cil->xc_cil_lock);
    ctx->commit_lsn = commit_lsn;
    wake_up_all(&cil->xc_commit_wait);
    spin_unlock(&cil->xc_cil_lock);

    /* release the hounds! */
    return xfs_log_release_iclog(log->l_mp, commit_iclog);

out_skip:
    up_write(&cil->xc_ctx_lock);
    xfs_log_ticket_put(new_ctx->ticket);
    kmem_free(new_ctx);
    return 0;

out_abort_free_ticket:
    xfs_log_ticket_put(tic);
out_abort:
    xlog_cil_committed(ctx, XFS_LI_ABORTED);
    return XFS_ERROR(EIO);
}

static void
xlog_cil_push_work(
    struct work_struct  *work)
{
    struct xfs_cil      *cil = container_of(work, struct xfs_cil,
                            xc_push_work);
    xlog_cil_push(cil->xc_log);
}

/*
 * We need to push CIL every so often so we don't cache more than we can fit in
 * the log. The limit really is that a checkpoint can't be more than half the
 * log (the current checkpoint is not allowed to overwrite the previous
 * checkpoint), but commit latency and memory usage limit this to a smaller
 * size.
 */
static void
xlog_cil_push_background(
    struct xlog *log)
{
    struct xfs_cil  *cil = log->l_cilp;

    /*
     * The cil won't be empty because we are called while holding the
     * context lock so whatever we added to the CIL will still be there
     */
    ASSERT(!list_empty(&cil->xc_cil));

    /*
     * don't do a background push if we haven't used up all the
     * space available yet.
     */
    if (cil->xc_ctx->space_used < XLOG_CIL_SPACE_LIMIT(log))
        return;

    spin_lock(&cil->xc_cil_lock);
    if (cil->xc_push_seq < cil->xc_current_sequence) {
        cil->xc_push_seq = cil->xc_current_sequence;
        queue_work(log->l_mp->m_cil_workqueue, &cil->xc_push_work);
    }
    spin_unlock(&cil->xc_cil_lock);

}

static void
xlog_cil_push_foreground(
    struct xlog *log,
    xfs_lsn_t   push_seq)
{
    struct xfs_cil  *cil = log->l_cilp;

    if (!cil)
        return;

    ASSERT(push_seq && push_seq <= cil->xc_current_sequence);

    /* start on any pending background push to minimise wait time on it */
    flush_work(&cil->xc_push_work);

    /*
     * If the CIL is empty or we've already pushed the sequence then
     * there's no work we need to do.
     */
    spin_lock(&cil->xc_cil_lock);
    if (list_empty(&cil->xc_cil) || push_seq <= cil->xc_push_seq) {
        spin_unlock(&cil->xc_cil_lock);
        return;
    }

    cil->xc_push_seq = push_seq;
    spin_unlock(&cil->xc_cil_lock);

    /* do the push now */
    xlog_cil_push(log);
}

/*
 * Commit a transaction with the given vector to the Committed Item List.
 *
 * To do this, we need to format the item, pin it in memory if required and
 * account for the space used by the transaction. Once we have done that we
 * need to release the unused reservation for the transaction, attach the
 * transaction to the checkpoint context so we carry the busy extents through
 * to checkpoint completion, and then unlock all the items in the transaction.
 *
 * For more specific information about the order of operations in
 * xfs_log_commit_cil() please refer to the comments in
 * xfs_trans_commit_iclog().
 *
 * Called with the context lock already held in read mode to lock out
 * background commit, returns without it held once background commits are
 * allowed again.
 */
int
xfs_log_commit_cil(
    struct xfs_mount    *mp,
    struct xfs_trans    *tp,
    xfs_lsn_t       *commit_lsn,
    int         flags)
{
    struct xlog     *log = mp->m_log;
    int         log_flags = 0;
    struct xfs_log_vec  *log_vector;

    if (flags & XFS_TRANS_RELEASE_LOG_RES)
        log_flags = XFS_LOG_REL_PERM_RESERV;

    /*
     * Do all the hard work of formatting items (including memory
     * allocation) outside the CIL context lock. This prevents stalling CIL
     * pushes when we are low on memory and a transaction commit spends a
     * lot of time in memory reclaim.
     */
    log_vector = xlog_cil_prepare_log_vecs(tp);
    if (!log_vector)
        return ENOMEM;

    /* lock out background commit */
    down_read(&log->l_cilp->xc_ctx_lock);
    if (commit_lsn)
        *commit_lsn = log->l_cilp->xc_ctx->sequence;

    xlog_cil_insert_items(log, log_vector, tp->t_ticket);

    /* check we didn't blow the reservation */
    if (tp->t_ticket->t_curr_res < 0)
        xlog_print_tic_res(log->l_mp, tp->t_ticket);

    /* attach the transaction to the CIL if it has any busy extents */
    if (!list_empty(&tp->t_busy)) {
        spin_lock(&log->l_cilp->xc_cil_lock);
        list_splice_init(&tp->t_busy,
                    &log->l_cilp->xc_ctx->busy_extents);
        spin_unlock(&log->l_cilp->xc_cil_lock);
    }

    tp->t_commit_lsn = *commit_lsn;
    xfs_log_done(mp, tp->t_ticket, NULL, log_flags);
    xfs_trans_unreserve_and_mod_sb(tp);

    /*
     * Once all the items of the transaction have been copied to the CIL,
     * the items can be unlocked and freed.
     *
     * This needs to be done before we drop the CIL context lock because we
     * have to update state in the log items and unlock them before they go
     * to disk. If we don't, then the CIL checkpoint can race with us and
     * we can run checkpoint completion before we've updated and unlocked
     * the log items. This affects (at least) processing of stale buffers,
     * inodes and EFIs.
     */
    xfs_trans_free_items(tp, *commit_lsn, 0);

    xlog_cil_push_background(log);

    up_read(&log->l_cilp->xc_ctx_lock);
    return 0;
}

/*
 * Conditionally push the CIL based on the sequence passed in.
 *
 * We only need to push if we haven't already pushed the sequence
 * number given. Hence the only time we will trigger a push here is
 * if the push sequence is the same as the current context.
 *
 * We return the current commit lsn to allow the callers to determine if a
 * iclog flush is necessary following this call.
 */
xfs_lsn_t
xlog_cil_force_lsn(
    struct xlog *log,
    xfs_lsn_t   sequence)
{
    struct xfs_cil      *cil = log->l_cilp;
    struct xfs_cil_ctx  *ctx;
    xfs_lsn_t       commit_lsn = NULLCOMMITLSN;

    ASSERT(sequence <= cil->xc_current_sequence);

    /*
     * check to see if we need to force out the current context.
     * xlog_cil_push() handles racing pushes for the same sequence,
     * so no need to deal with it here.
     */
    xlog_cil_push_foreground(log, sequence);

    /*
     * See if we can find a previous sequence still committing.
     * We need to wait for all previous sequence commits to complete
     * before allowing the force of push_seq to go ahead. Hence block
     * on commits for those as well.
     */
restart:
    spin_lock(&cil->xc_cil_lock);
    list_for_each_entry(ctx, &cil->xc_committing, committing) {
        if (ctx->sequence > sequence)
            continue;
        if (!ctx->commit_lsn) {
            /*
             * It is still being pushed! Wait for the push to
             * complete, then start again from the beginning.
             */
            xlog_wait(&cil->xc_commit_wait, &cil->xc_cil_lock);
            goto restart;
        }
        if (ctx->sequence != sequence)
            continue;
        /* found it! */
        commit_lsn = ctx->commit_lsn;
    }
    spin_unlock(&cil->xc_cil_lock);
    return commit_lsn;
}

/*
 * Check if the current log item was first committed in this sequence.
 * We can't rely on just the log item being in the CIL, we have to check
 * the recorded commit sequence number.
 *
 * Note: for this to be used in a non-racy manner, it has to be called with
 * CIL flushing locked out. As a result, it should only be used during the
 * transaction commit process when deciding what to format into the item.
 */
bool
xfs_log_item_in_current_chkpt(
    struct xfs_log_item *lip)
{
    struct xfs_cil_ctx *ctx;

    if (list_empty(&lip->li_cil))
        return false;

    ctx = lip->li_mountp->m_log->l_cilp->xc_ctx;

    /*
     * li_seq is written on the first commit of a log item to record the
     * first checkpoint it is written to. Hence if it is different to the
     * current sequence, we're in a new checkpoint.
     */
    if (XFS_LSN_CMP(lip->li_seq, ctx->sequence) != 0)
        return false;
    return true;
}

/*
 * Perform initial CIL structure initialisation.
 */
int
xlog_cil_init(
    struct xlog *log)
{
    struct xfs_cil  *cil;
    struct xfs_cil_ctx *ctx;

    cil = kmem_zalloc(sizeof(*cil), KM_SLEEP|KM_MAYFAIL);
    if (!cil)
        return ENOMEM;

    ctx = kmem_zalloc(sizeof(*ctx), KM_SLEEP|KM_MAYFAIL);
    if (!ctx) {
        kmem_free(cil);
        return ENOMEM;
    }

    INIT_WORK(&cil->xc_push_work, xlog_cil_push_work);
    INIT_LIST_HEAD(&cil->xc_cil);
    INIT_LIST_HEAD(&cil->xc_committing);
    spin_lock_init(&cil->xc_cil_lock);
    init_rwsem(&cil->xc_ctx_lock);
    init_waitqueue_head(&cil->xc_commit_wait);

    INIT_LIST_HEAD(&ctx->committing);
    INIT_LIST_HEAD(&ctx->busy_extents);
    ctx->sequence = 1;
    ctx->cil = cil;
    cil->xc_ctx = ctx;
    cil->xc_current_sequence = ctx->sequence;

    cil->xc_log = log;
    log->l_cilp = cil;
    return 0;
}

void
xlog_cil_destroy(
    struct xlog *log)
{
    if (log->l_cilp->xc_ctx) {
        if (log->l_cilp->xc_ctx->ticket)
            xfs_log_ticket_put(log->l_cilp->xc_ctx->ticket);
        kmem_free(log->l_cilp->xc_ctx);
    }

    ASSERT(list_empty(&log->l_cilp->xc_cil));
    kmem_free(log->l_cilp);
}