Merge branch 'nvme-4.18' of git://git.infradead.org/nvme into for-linus

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

/*
 * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
 * Copyright (c) 2008 Dave Chinner
 * 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_format.h"
#include "xfs_log_format.h"
#include "xfs_trans_resv.h"
#include "xfs_mount.h"
#include "xfs_trans.h"
#include "xfs_trans_priv.h"
#include "xfs_trace.h"
#include "xfs_errortag.h"
#include "xfs_error.h"
#include "xfs_log.h"

#ifdef DEBUG
/*
 * Check that the list is sorted as it should be.
 *
 * Called with the ail lock held, but we don't want to assert fail with it
 * held otherwise we'll lock everything up and won't be able to debug the
 * cause. Hence we sample and check the state under the AIL lock and return if
 * everything is fine, otherwise we drop the lock and run the ASSERT checks.
 * Asserts may not be fatal, so pick the lock back up and continue onwards.
 */
STATIC void
xfs_ail_check(
        struct xfs_ail          *ailp,
        struct xfs_log_item     *lip)
{
        struct xfs_log_item     *prev_lip;
        struct xfs_log_item     *next_lip;
        xfs_lsn_t               prev_lsn = NULLCOMMITLSN;
        xfs_lsn_t               next_lsn = NULLCOMMITLSN;
        xfs_lsn_t               lsn;
        bool                    in_ail;


        if (list_empty(&ailp->ail_head))
                return;

        /*
         * Sample then check the next and previous entries are valid.
         */
        in_ail = test_bit(XFS_LI_IN_AIL, &lip->li_flags);
        prev_lip = list_entry(lip->li_ail.prev, struct xfs_log_item, li_ail);
        if (&prev_lip->li_ail != &ailp->ail_head)
                prev_lsn = prev_lip->li_lsn;
        next_lip = list_entry(lip->li_ail.next, struct xfs_log_item, li_ail);
        if (&next_lip->li_ail != &ailp->ail_head)
                next_lsn = next_lip->li_lsn;
        lsn = lip->li_lsn;

        if (in_ail &&
            (prev_lsn == NULLCOMMITLSN || XFS_LSN_CMP(prev_lsn, lsn) <= 0) &&
            (next_lsn == NULLCOMMITLSN || XFS_LSN_CMP(next_lsn, lsn) >= 0))
                return;

        spin_unlock(&ailp->ail_lock);
        ASSERT(in_ail);
        ASSERT(prev_lsn == NULLCOMMITLSN || XFS_LSN_CMP(prev_lsn, lsn) <= 0);
        ASSERT(next_lsn == NULLCOMMITLSN || XFS_LSN_CMP(next_lsn, lsn) >= 0);
        spin_lock(&ailp->ail_lock);
}
#else /* !DEBUG */
#define xfs_ail_check(a,l)
#endif /* DEBUG */

/*
 * Return a pointer to the last item in the AIL.  If the AIL is empty, then
 * return NULL.
 */
static xfs_log_item_t *
xfs_ail_max(
        struct xfs_ail  *ailp)
{
        if (list_empty(&ailp->ail_head))
                return NULL;

        return list_entry(ailp->ail_head.prev, xfs_log_item_t, li_ail);
}

/*
 * Return a pointer to the item which follows the given item in the AIL.  If
 * the given item is the last item in the list, then return NULL.
 */
static xfs_log_item_t *
xfs_ail_next(
        struct xfs_ail  *ailp,
        xfs_log_item_t  *lip)
{
        if (lip->li_ail.next == &ailp->ail_head)
                return NULL;

        return list_first_entry(&lip->li_ail, xfs_log_item_t, li_ail);
}

/*
 * This is called by the log manager code to determine the LSN of the tail of
 * the log.  This is exactly the LSN of the first item in the AIL.  If the AIL
 * is empty, then this function returns 0.
 *
 * We need the AIL lock in order to get a coherent read of the lsn of the last
 * item in the AIL.
 */
xfs_lsn_t
xfs_ail_min_lsn(
        struct xfs_ail  *ailp)
{
        xfs_lsn_t       lsn = 0;
        xfs_log_item_t  *lip;

        spin_lock(&ailp->ail_lock);
        lip = xfs_ail_min(ailp);
        if (lip)
                lsn = lip->li_lsn;
        spin_unlock(&ailp->ail_lock);

        return lsn;
}

/*
 * Return the maximum lsn held in the AIL, or zero if the AIL is empty.
 */
static xfs_lsn_t
xfs_ail_max_lsn(
        struct xfs_ail  *ailp)
{
        xfs_lsn_t       lsn = 0;
        xfs_log_item_t  *lip;

        spin_lock(&ailp->ail_lock);
        lip = xfs_ail_max(ailp);
        if (lip)
                lsn = lip->li_lsn;
        spin_unlock(&ailp->ail_lock);

        return lsn;
}

/*
 * The cursor keeps track of where our current traversal is up to by tracking
 * the next item in the list for us. However, for this to be safe, removing an
 * object from the AIL needs to invalidate any cursor that points to it. hence
 * the traversal cursor needs to be linked to the struct xfs_ail so that
 * deletion can search all the active cursors for invalidation.
 */
STATIC void
xfs_trans_ail_cursor_init(
        struct xfs_ail          *ailp,
        struct xfs_ail_cursor   *cur)
{
        cur->item = NULL;
        list_add_tail(&cur->list, &ailp->ail_cursors);
}

/*
 * Get the next item in the traversal and advance the cursor.  If the cursor
 * was invalidated (indicated by a lip of 1), restart the traversal.
 */
struct xfs_log_item *
xfs_trans_ail_cursor_next(
        struct xfs_ail          *ailp,
        struct xfs_ail_cursor   *cur)
{
        struct xfs_log_item     *lip = cur->item;

        if ((uintptr_t)lip & 1)
                lip = xfs_ail_min(ailp);
        if (lip)
                cur->item = xfs_ail_next(ailp, lip);
        return lip;
}

/*
 * When the traversal is complete, we need to remove the cursor from the list
 * of traversing cursors.
 */
void
xfs_trans_ail_cursor_done(
        struct xfs_ail_cursor   *cur)
{
        cur->item = NULL;
        list_del_init(&cur->list);
}

/*
 * Invalidate any cursor that is pointing to this item. This is called when an
 * item is removed from the AIL. Any cursor pointing to this object is now
 * invalid and the traversal needs to be terminated so it doesn't reference a
 * freed object. We set the low bit of the cursor item pointer so we can
 * distinguish between an invalidation and the end of the list when getting the
 * next item from the cursor.
 */
STATIC void
xfs_trans_ail_cursor_clear(
        struct xfs_ail          *ailp,
        struct xfs_log_item     *lip)
{
        struct xfs_ail_cursor   *cur;

        list_for_each_entry(cur, &ailp->ail_cursors, list) {
                if (cur->item == lip)
                        cur->item = (struct xfs_log_item *)
                                        ((uintptr_t)cur->item | 1);
        }
}

/*
 * Find the first item in the AIL with the given @lsn by searching in ascending
 * LSN order and initialise the cursor to point to the next item for a
 * ascending traversal.  Pass a @lsn of zero to initialise the cursor to the
 * first item in the AIL. Returns NULL if the list is empty.
 */
xfs_log_item_t *
xfs_trans_ail_cursor_first(
        struct xfs_ail          *ailp,
        struct xfs_ail_cursor   *cur,
        xfs_lsn_t               lsn)
{
        xfs_log_item_t          *lip;

        xfs_trans_ail_cursor_init(ailp, cur);

        if (lsn == 0) {
                lip = xfs_ail_min(ailp);
                goto out;
        }

        list_for_each_entry(lip, &ailp->ail_head, li_ail) {
                if (XFS_LSN_CMP(lip->li_lsn, lsn) >= 0)
                        goto out;
        }
        return NULL;

out:
        if (lip)
                cur->item = xfs_ail_next(ailp, lip);
        return lip;
}

static struct xfs_log_item *
__xfs_trans_ail_cursor_last(
        struct xfs_ail          *ailp,
        xfs_lsn_t               lsn)
{
        xfs_log_item_t          *lip;

        list_for_each_entry_reverse(lip, &ailp->ail_head, li_ail) {
                if (XFS_LSN_CMP(lip->li_lsn, lsn) <= 0)
                        return lip;
        }
        return NULL;
}

/*
 * Find the last item in the AIL with the given @lsn by searching in descending
 * LSN order and initialise the cursor to point to that item.  If there is no
 * item with the value of @lsn, then it sets the cursor to the last item with an
 * LSN lower than @lsn.  Returns NULL if the list is empty.
 */
struct xfs_log_item *
xfs_trans_ail_cursor_last(
        struct xfs_ail          *ailp,
        struct xfs_ail_cursor   *cur,
        xfs_lsn_t               lsn)
{
        xfs_trans_ail_cursor_init(ailp, cur);
        cur->item = __xfs_trans_ail_cursor_last(ailp, lsn);
        return cur->item;
}

/*
 * Splice the log item list into the AIL at the given LSN. We splice to the
 * tail of the given LSN to maintain insert order for push traversals. The
 * cursor is optional, allowing repeated updates to the same LSN to avoid
 * repeated traversals.  This should not be called with an empty list.
 */
static void
xfs_ail_splice(
        struct xfs_ail          *ailp,
        struct xfs_ail_cursor   *cur,
        struct list_head        *list,
        xfs_lsn_t               lsn)
{
        struct xfs_log_item     *lip;

        ASSERT(!list_empty(list));

        /*
         * Use the cursor to determine the insertion point if one is
         * provided.  If not, or if the one we got is not valid,
         * find the place in the AIL where the items belong.
         */
        lip = cur ? cur->item : NULL;
        if (!lip || (uintptr_t)lip & 1)
                lip = __xfs_trans_ail_cursor_last(ailp, lsn);

        /*
         * If a cursor is provided, we know we're processing the AIL
         * in lsn order, and future items to be spliced in will
         * follow the last one being inserted now.  Update the
         * cursor to point to that last item, now while we have a
         * reliable pointer to it.
         */
        if (cur)
                cur->item = list_entry(list->prev, struct xfs_log_item, li_ail);

        /*
         * Finally perform the splice.  Unless the AIL was empty,
         * lip points to the item in the AIL _after_ which the new
         * items should go.  If lip is null the AIL was empty, so
         * the new items go at the head of the AIL.
         */
        if (lip)
                list_splice(list, &lip->li_ail);
        else
                list_splice(list, &ailp->ail_head);
}

/*
 * Delete the given item from the AIL.  Return a pointer to the item.
 */
static void
xfs_ail_delete(
        struct xfs_ail  *ailp,
        xfs_log_item_t  *lip)
{
        xfs_ail_check(ailp, lip);
        list_del(&lip->li_ail);
        xfs_trans_ail_cursor_clear(ailp, lip);
}

static inline uint
xfsaild_push_item(
        struct xfs_ail          *ailp,
        struct xfs_log_item     *lip)
{
        /*
         * If log item pinning is enabled, skip the push and track the item as
         * pinned. This can help induce head-behind-tail conditions.
         */
        if (XFS_TEST_ERROR(false, ailp->ail_mount, XFS_ERRTAG_LOG_ITEM_PIN))
                return XFS_ITEM_PINNED;

        return lip->li_ops->iop_push(lip, &ailp->ail_buf_list);
}

static long
xfsaild_push(
        struct xfs_ail          *ailp)
{
        xfs_mount_t             *mp = ailp->ail_mount;
        struct xfs_ail_cursor   cur;
        xfs_log_item_t          *lip;
        xfs_lsn_t               lsn;
        xfs_lsn_t               target;
        long                    tout;
        int                     stuck = 0;
        int                     flushing = 0;
        int                     count = 0;

        /*
         * If we encountered pinned items or did not finish writing out all
         * buffers the last time we ran, force the log first and wait for it
         * before pushing again.
         */
        if (ailp->ail_log_flush && ailp->ail_last_pushed_lsn == 0 &&
            (!list_empty_careful(&ailp->ail_buf_list) ||
             xfs_ail_min_lsn(ailp))) {
                ailp->ail_log_flush = 0;

                XFS_STATS_INC(mp, xs_push_ail_flush);
                xfs_log_force(mp, XFS_LOG_SYNC);
        }

        spin_lock(&ailp->ail_lock);

        /* barrier matches the ail_target update in xfs_ail_push() */
        smp_rmb();
        target = ailp->ail_target;
        ailp->ail_target_prev = target;

        lip = xfs_trans_ail_cursor_first(ailp, &cur, ailp->ail_last_pushed_lsn);
        if (!lip) {
                /*
                 * If the AIL is empty or our push has reached the end we are
                 * done now.
                 */
                xfs_trans_ail_cursor_done(&cur);
                spin_unlock(&ailp->ail_lock);
                goto out_done;
        }

        XFS_STATS_INC(mp, xs_push_ail);

        lsn = lip->li_lsn;
        while ((XFS_LSN_CMP(lip->li_lsn, target) <= 0)) {
                int     lock_result;

                /*
                 * Note that iop_push may unlock and reacquire the AIL lock.  We
                 * rely on the AIL cursor implementation to be able to deal with
                 * the dropped lock.
                 */
                lock_result = xfsaild_push_item(ailp, lip);
                switch (lock_result) {
                case XFS_ITEM_SUCCESS:
                        XFS_STATS_INC(mp, xs_push_ail_success);
                        trace_xfs_ail_push(lip);

                        ailp->ail_last_pushed_lsn = lsn;
                        break;

                case XFS_ITEM_FLUSHING:
                        /*
                         * The item or its backing buffer is already beeing
                         * flushed.  The typical reason for that is that an
                         * inode buffer is locked because we already pushed the
                         * updates to it as part of inode clustering.
                         *
                         * We do not want to to stop flushing just because lots
                         * of items are already beeing flushed, but we need to
                         * re-try the flushing relatively soon if most of the
                         * AIL is beeing flushed.
                         */
                        XFS_STATS_INC(mp, xs_push_ail_flushing);
                        trace_xfs_ail_flushing(lip);

                        flushing++;
                        ailp->ail_last_pushed_lsn = lsn;
                        break;

                case XFS_ITEM_PINNED:
                        XFS_STATS_INC(mp, xs_push_ail_pinned);
                        trace_xfs_ail_pinned(lip);

                        stuck++;
                        ailp->ail_log_flush++;
                        break;
                case XFS_ITEM_LOCKED:
                        XFS_STATS_INC(mp, xs_push_ail_locked);
                        trace_xfs_ail_locked(lip);

                        stuck++;
                        break;
                default:
                        ASSERT(0);
                        break;
                }

                count++;

                /*
                 * Are there too many items we can't do anything with?
                 *
                 * If we we are skipping too many items because we can't flush
                 * them or they are already being flushed, we back off and
                 * given them time to complete whatever operation is being
                 * done. i.e. remove pressure from the AIL while we can't make
                 * progress so traversals don't slow down further inserts and
                 * removals to/from the AIL.
                 *
                 * The value of 100 is an arbitrary magic number based on
                 * observation.
                 */
                if (stuck > 100)
                        break;

                lip = xfs_trans_ail_cursor_next(ailp, &cur);
                if (lip == NULL)
                        break;
                lsn = lip->li_lsn;
        }
        xfs_trans_ail_cursor_done(&cur);
        spin_unlock(&ailp->ail_lock);

        if (xfs_buf_delwri_submit_nowait(&ailp->ail_buf_list))
                ailp->ail_log_flush++;

        if (!count || XFS_LSN_CMP(lsn, target) >= 0) {
out_done:
                /*
                 * We reached the target or the AIL is empty, so wait a bit
                 * longer for I/O to complete and remove pushed items from the
                 * AIL before we start the next scan from the start of the AIL.
                 */
                tout = 50;
                ailp->ail_last_pushed_lsn = 0;
        } else if (((stuck + flushing) * 100) / count > 90) {
                /*
                 * Either there is a lot of contention on the AIL or we are
                 * stuck due to operations in progress. "Stuck" in this case
                 * is defined as >90% of the items we tried to push were stuck.
                 *
                 * Backoff a bit more to allow some I/O to complete before
                 * restarting from the start of the AIL. This prevents us from
                 * spinning on the same items, and if they are pinned will all
                 * the restart to issue a log force to unpin the stuck items.
                 */
                tout = 20;
                ailp->ail_last_pushed_lsn = 0;
        } else {
                /*
                 * Assume we have more work to do in a short while.
                 */
                tout = 10;
        }

        return tout;
}

static int
xfsaild(
        void            *data)
{
        struct xfs_ail  *ailp = data;
        long            tout = 0;       /* milliseconds */

        current->flags |= PF_MEMALLOC;
        set_freezable();

        while (1) {
                if (tout && tout <= 20)
                        set_current_state(TASK_KILLABLE);
                else
                        set_current_state(TASK_INTERRUPTIBLE);

                /*
                 * Check kthread_should_stop() after we set the task state
                 * to guarantee that we either see the stop bit and exit or
                 * the task state is reset to runnable such that it's not
                 * scheduled out indefinitely and detects the stop bit at
                 * next iteration.
                 *
                 * A memory barrier is included in above task state set to
                 * serialize again kthread_stop().
                 */
                if (kthread_should_stop()) {
                        __set_current_state(TASK_RUNNING);
                        break;
                }

                spin_lock(&ailp->ail_lock);

                /*
                 * Idle if the AIL is empty and we are not racing with a target
                 * update. We check the AIL after we set the task to a sleep
                 * state to guarantee that we either catch an ail_target update
                 * or that a wake_up resets the state to TASK_RUNNING.
                 * Otherwise, we run the risk of sleeping indefinitely.
                 *
                 * The barrier matches the ail_target update in xfs_ail_push().
                 */
                smp_rmb();
                if (!xfs_ail_min(ailp) &&
                    ailp->ail_target == ailp->ail_target_prev) {
                        spin_unlock(&ailp->ail_lock);
                        freezable_schedule();
                        tout = 0;
                        continue;
                }
                spin_unlock(&ailp->ail_lock);

                if (tout)
                        freezable_schedule_timeout(msecs_to_jiffies(tout));

                __set_current_state(TASK_RUNNING);

                try_to_freeze();

                tout = xfsaild_push(ailp);
        }

        return 0;
}

/*
 * This routine is called to move the tail of the AIL forward.  It does this by
 * trying to flush items in the AIL whose lsns are below the given
 * threshold_lsn.
 *
 * The push is run asynchronously in a workqueue, which means the caller needs
 * to handle waiting on the async flush for space to become available.
 * We don't want to interrupt any push that is in progress, hence we only queue
 * work if we set the pushing bit approriately.
 *
 * We do this unlocked - we only need to know whether there is anything in the
 * AIL at the time we are called. We don't need to access the contents of
 * any of the objects, so the lock is not needed.
 */
void
xfs_ail_push(
        struct xfs_ail  *ailp,
        xfs_lsn_t       threshold_lsn)
{
        xfs_log_item_t  *lip;

        lip = xfs_ail_min(ailp);
        if (!lip || XFS_FORCED_SHUTDOWN(ailp->ail_mount) ||
            XFS_LSN_CMP(threshold_lsn, ailp->ail_target) <= 0)
                return;

        /*
         * Ensure that the new target is noticed in push code before it clears
         * the XFS_AIL_PUSHING_BIT.
         */
        smp_wmb();
        xfs_trans_ail_copy_lsn(ailp, &ailp->ail_target, &threshold_lsn);
        smp_wmb();

        wake_up_process(ailp->ail_task);
}

/*
 * Push out all items in the AIL immediately
 */
void
xfs_ail_push_all(
        struct xfs_ail  *ailp)
{
        xfs_lsn_t       threshold_lsn = xfs_ail_max_lsn(ailp);

        if (threshold_lsn)
                xfs_ail_push(ailp, threshold_lsn);
}

/*
 * Push out all items in the AIL immediately and wait until the AIL is empty.
 */
void
xfs_ail_push_all_sync(
        struct xfs_ail  *ailp)
{
        struct xfs_log_item     *lip;
        DEFINE_WAIT(wait);

        spin_lock(&ailp->ail_lock);
        while ((lip = xfs_ail_max(ailp)) != NULL) {
                prepare_to_wait(&ailp->ail_empty, &wait, TASK_UNINTERRUPTIBLE);
                ailp->ail_target = lip->li_lsn;
                wake_up_process(ailp->ail_task);
                spin_unlock(&ailp->ail_lock);
                schedule();
                spin_lock(&ailp->ail_lock);
        }
        spin_unlock(&ailp->ail_lock);

        finish_wait(&ailp->ail_empty, &wait);
}

/*
 * xfs_trans_ail_update - bulk AIL insertion operation.
 *
 * @xfs_trans_ail_update takes an array of log items that all need to be
 * positioned at the same LSN in the AIL. If an item is not in the AIL, it will
 * be added.  Otherwise, it will be repositioned  by removing it and re-adding
 * it to the AIL. If we move the first item in the AIL, update the log tail to
 * match the new minimum LSN in the AIL.
 *
 * This function takes the AIL lock once to execute the update operations on
 * all the items in the array, and as such should not be called with the AIL
 * lock held. As a result, once we have the AIL lock, we need to check each log
 * item LSN to confirm it needs to be moved forward in the AIL.
 *
 * To optimise the insert operation, we delete all the items from the AIL in
 * the first pass, moving them into a temporary list, then splice the temporary
 * list into the correct position in the AIL. This avoids needing to do an
 * insert operation on every item.
 *
 * This function must be called with the AIL lock held.  The lock is dropped
 * before returning.
 */
void
xfs_trans_ail_update_bulk(
        struct xfs_ail          *ailp,
        struct xfs_ail_cursor   *cur,
        struct xfs_log_item     **log_items,
        int                     nr_items,
        xfs_lsn_t               lsn) __releases(ailp->ail_lock)
{
        xfs_log_item_t          *mlip;
        int                     mlip_changed = 0;
        int                     i;
        LIST_HEAD(tmp);

        ASSERT(nr_items > 0);           /* Not required, but true. */
        mlip = xfs_ail_min(ailp);

        for (i = 0; i < nr_items; i++) {
                struct xfs_log_item *lip = log_items[i];
                if (test_and_set_bit(XFS_LI_IN_AIL, &lip->li_flags)) {
                        /* check if we really need to move the item */
                        if (XFS_LSN_CMP(lsn, lip->li_lsn) <= 0)
                                continue;

                        trace_xfs_ail_move(lip, lip->li_lsn, lsn);
                        xfs_ail_delete(ailp, lip);
                        if (mlip == lip)
                                mlip_changed = 1;
                } else {
                        trace_xfs_ail_insert(lip, 0, lsn);
                }
                lip->li_lsn = lsn;
                list_add(&lip->li_ail, &tmp);
        }

        if (!list_empty(&tmp))
                xfs_ail_splice(ailp, cur, &tmp, lsn);

        if (mlip_changed) {
                if (!XFS_FORCED_SHUTDOWN(ailp->ail_mount))
                        xlog_assign_tail_lsn_locked(ailp->ail_mount);
                spin_unlock(&ailp->ail_lock);

                xfs_log_space_wake(ailp->ail_mount);
        } else {
                spin_unlock(&ailp->ail_lock);
        }
}

bool
xfs_ail_delete_one(
        struct xfs_ail          *ailp,
        struct xfs_log_item     *lip)
{
        struct xfs_log_item     *mlip = xfs_ail_min(ailp);

        trace_xfs_ail_delete(lip, mlip->li_lsn, lip->li_lsn);
        xfs_ail_delete(ailp, lip);
        xfs_clear_li_failed(lip);
        clear_bit(XFS_LI_IN_AIL, &lip->li_flags);
        lip->li_lsn = 0;

        return mlip == lip;
}

/**
 * Remove a log items from the AIL
 *
 * @xfs_trans_ail_delete_bulk takes an array of log items that all need to
 * removed from the AIL. The caller is already holding the AIL lock, and done
 * all the checks necessary to ensure the items passed in via @log_items are
 * ready for deletion. This includes checking that the items are in the AIL.
 *
 * For each log item to be removed, unlink it  from the AIL, clear the IN_AIL
 * flag from the item and reset the item's lsn to 0. If we remove the first
 * item in the AIL, update the log tail to match the new minimum LSN in the
 * AIL.
 *
 * This function will not drop the AIL lock until all items are removed from
 * the AIL to minimise the amount of lock traffic on the AIL. This does not
 * greatly increase the AIL hold time, but does significantly reduce the amount
 * of traffic on the lock, especially during IO completion.
 *
 * This function must be called with the AIL lock held.  The lock is dropped
 * before returning.
 */
void
xfs_trans_ail_delete(
        struct xfs_ail          *ailp,
        struct xfs_log_item     *lip,
        int                     shutdown_type) __releases(ailp->ail_lock)
{
        struct xfs_mount        *mp = ailp->ail_mount;
        bool                    mlip_changed;

        if (!test_bit(XFS_LI_IN_AIL, &lip->li_flags)) {
                spin_unlock(&ailp->ail_lock);
                if (!XFS_FORCED_SHUTDOWN(mp)) {
                        xfs_alert_tag(mp, XFS_PTAG_AILDELETE,
        "%s: attempting to delete a log item that is not in the AIL",
                                        __func__);
                        xfs_force_shutdown(mp, shutdown_type);
                }
                return;
        }

        mlip_changed = xfs_ail_delete_one(ailp, lip);
        if (mlip_changed) {
                if (!XFS_FORCED_SHUTDOWN(mp))
                        xlog_assign_tail_lsn_locked(mp);
                if (list_empty(&ailp->ail_head))
                        wake_up_all(&ailp->ail_empty);
        }

        spin_unlock(&ailp->ail_lock);
        if (mlip_changed)
                xfs_log_space_wake(ailp->ail_mount);
}

int
xfs_trans_ail_init(
        xfs_mount_t     *mp)
{
        struct xfs_ail  *ailp;

        ailp = kmem_zalloc(sizeof(struct xfs_ail), KM_MAYFAIL);
        if (!ailp)
                return -ENOMEM;

        ailp->ail_mount = mp;
        INIT_LIST_HEAD(&ailp->ail_head);
        INIT_LIST_HEAD(&ailp->ail_cursors);
        spin_lock_init(&ailp->ail_lock);
        INIT_LIST_HEAD(&ailp->ail_buf_list);
        init_waitqueue_head(&ailp->ail_empty);

        ailp->ail_task = kthread_run(xfsaild, ailp, "xfsaild/%s",
                        ailp->ail_mount->m_fsname);
        if (IS_ERR(ailp->ail_task))
                goto out_free_ailp;

        mp->m_ail = ailp;
        return 0;

out_free_ailp:
        kmem_free(ailp);
        return -ENOMEM;
}

void
xfs_trans_ail_destroy(
        xfs_mount_t     *mp)
{
        struct xfs_ail  *ailp = mp->m_ail;

        kthread_stop(ailp->ail_task);
        kmem_free(ailp);
}