sched: make early bootup sched_clock() use safer

[wrt350n-kernel.git] / fs / xfs / xfs_trans_ail.c

/*
 * Copyright (c) 2000-2002,2005 Silicon Graphics, Inc.
 * All Rights Reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it would be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write the Free Software Foundation,
 * Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 */
#include "xfs.h"
#include "xfs_fs.h"
#include "xfs_types.h"
#include "xfs_log.h"
#include "xfs_inum.h"
#include "xfs_trans.h"
#include "xfs_sb.h"
#include "xfs_ag.h"
#include "xfs_dmapi.h"
#include "xfs_mount.h"
#include "xfs_trans_priv.h"
#include "xfs_error.h"

STATIC void xfs_ail_insert(xfs_ail_entry_t *, xfs_log_item_t *);
STATIC xfs_log_item_t * xfs_ail_delete(xfs_ail_entry_t *, xfs_log_item_t *);
STATIC xfs_log_item_t * xfs_ail_min(xfs_ail_entry_t *);
STATIC xfs_log_item_t * xfs_ail_next(xfs_ail_entry_t *, xfs_log_item_t *);

#ifdef DEBUG
STATIC void xfs_ail_check(xfs_ail_entry_t *, xfs_log_item_t *);
#else
#define xfs_ail_check(a,l)
#endif /* DEBUG */


/*
 * 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_trans_tail_ail(
        xfs_mount_t     *mp)
{
        xfs_lsn_t       lsn;
        xfs_log_item_t  *lip;

        spin_lock(&mp->m_ail_lock);
        lip = xfs_ail_min(&(mp->m_ail.xa_ail));
        if (lip == NULL) {
                lsn = (xfs_lsn_t)0;
        } else {
                lsn = lip->li_lsn;
        }
        spin_unlock(&mp->m_ail_lock);

        return lsn;
}

/*
 * xfs_trans_push_ail
 *
 * 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 separate thread, so we return the tail
 * of the log right now instead of the tail after the push. This means we will
 * either continue right away, or we will sleep waiting on the async thread to
 * do it's work.
 *
 * 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_trans_push_ail(
        xfs_mount_t             *mp,
        xfs_lsn_t               threshold_lsn)
{
        xfs_log_item_t          *lip;

        lip = xfs_ail_min(&mp->m_ail.xa_ail);
        if (lip && !XFS_FORCED_SHUTDOWN(mp)) {
                if (XFS_LSN_CMP(threshold_lsn, mp->m_ail.xa_target) > 0)
                        xfsaild_wakeup(mp, threshold_lsn);
        }
}

/*
 * Return the item in the AIL with the current lsn.
 * Return the current tree generation number for use
 * in calls to xfs_trans_next_ail().
 */
STATIC xfs_log_item_t *
xfs_trans_first_push_ail(
        xfs_mount_t     *mp,
        int             *gen,
        xfs_lsn_t       lsn)
{
        xfs_log_item_t  *lip;

        lip = xfs_ail_min(&(mp->m_ail.xa_ail));
        *gen = (int)mp->m_ail.xa_gen;
        if (lsn == 0)
                return lip;

        while (lip && (XFS_LSN_CMP(lip->li_lsn, lsn) < 0))
                lip = lip->li_ail.ail_forw;

        return lip;
}

/*
 * Function that does the work of pushing on the AIL
 */
long
xfsaild_push(
        xfs_mount_t     *mp,
        xfs_lsn_t       *last_lsn)
{
        long            tout = 1000; /* milliseconds */
        xfs_lsn_t       last_pushed_lsn = *last_lsn;
        xfs_lsn_t       target =  mp->m_ail.xa_target;
        xfs_lsn_t       lsn;
        xfs_log_item_t  *lip;
        int             gen;
        int             restarts;
        int             flush_log, count, stuck;

#define XFS_TRANS_PUSH_AIL_RESTARTS     10

        spin_lock(&mp->m_ail_lock);
        lip = xfs_trans_first_push_ail(mp, &gen, *last_lsn);
        if (!lip || XFS_FORCED_SHUTDOWN(mp)) {
                /*
                 * AIL is empty or our push has reached the end.
                 */
                spin_unlock(&mp->m_ail_lock);
                last_pushed_lsn = 0;
                goto out;
        }

        XFS_STATS_INC(xs_push_ail);

        /*
         * While the item we are looking at is below the given threshold
         * try to flush it out. We'd like not to stop until we've at least
         * tried to push on everything in the AIL with an LSN less than
         * the given threshold.
         *
         * However, we will stop after a certain number of pushes and wait
         * for a reduced timeout to fire before pushing further. This
         * prevents use from spinning when we can't do anything or there is
         * lots of contention on the AIL lists.
         */
        tout = 10;
        lsn = lip->li_lsn;
        flush_log = stuck = count = restarts = 0;
        while ((XFS_LSN_CMP(lip->li_lsn, target) < 0)) {
                int     lock_result;
                /*
                 * If we can lock the item without sleeping, unlock the AIL
                 * lock and flush the item.  Then re-grab the AIL lock so we
                 * can look for the next item on the AIL. List changes are
                 * handled by the AIL lookup functions internally
                 *
                 * If we can't lock the item, either its holder will flush it
                 * or it is already being flushed or it is being relogged.  In
                 * any of these case it is being taken care of and we can just
                 * skip to the next item in the list.
                 */
                lock_result = IOP_TRYLOCK(lip);
                spin_unlock(&mp->m_ail_lock);
                switch (lock_result) {
                case XFS_ITEM_SUCCESS:
                        XFS_STATS_INC(xs_push_ail_success);
                        IOP_PUSH(lip);
                        last_pushed_lsn = lsn;
                        break;

                case XFS_ITEM_PUSHBUF:
                        XFS_STATS_INC(xs_push_ail_pushbuf);
                        IOP_PUSHBUF(lip);
                        last_pushed_lsn = lsn;
                        break;

                case XFS_ITEM_PINNED:
                        XFS_STATS_INC(xs_push_ail_pinned);
                        stuck++;
                        flush_log = 1;
                        break;

                case XFS_ITEM_LOCKED:
                        XFS_STATS_INC(xs_push_ail_locked);
                        last_pushed_lsn = lsn;
                        stuck++;
                        break;

                case XFS_ITEM_FLUSHING:
                        XFS_STATS_INC(xs_push_ail_flushing);
                        last_pushed_lsn = lsn;
                        stuck++;
                        break;

                default:
                        ASSERT(0);
                        break;
                }

                spin_lock(&mp->m_ail_lock);
                /* should we bother continuing? */
                if (XFS_FORCED_SHUTDOWN(mp))
                        break;
                ASSERT(mp->m_log);

                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_next_ail(mp, lip, &gen, &restarts);
                if (lip == NULL)
                        break;
                if (restarts > XFS_TRANS_PUSH_AIL_RESTARTS)
                        break;
                lsn = lip->li_lsn;
        }
        spin_unlock(&mp->m_ail_lock);

        if (flush_log) {
                /*
                 * If something we need to push out was pinned, then
                 * push out the log so it will become unpinned and
                 * move forward in the AIL.
                 */
                XFS_STATS_INC(xs_push_ail_flush);
                xfs_log_force(mp, (xfs_lsn_t)0, XFS_LOG_FORCE);
        }

        /*
         * We reached the target 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.
         */
        if ((XFS_LSN_CMP(lsn, target) >= 0)) {
                tout += 20;
                last_pushed_lsn = 0;
        } else if ((restarts > XFS_TRANS_PUSH_AIL_RESTARTS) ||
                   (count && ((stuck * 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
                 * continuing from where we were.
                 */
                tout += 10;
        }
out:
        *last_lsn = last_pushed_lsn;
        return tout;
}       /* xfsaild_push */


/*
 * This is to be called when an item is unlocked that may have
 * been in the AIL.  It will wake up the first member of the AIL
 * wait list if this item's unlocking might allow it to progress.
 * If the item is in the AIL, then we need to get the AIL lock
 * while doing our checking so we don't race with someone going
 * to sleep waiting for this event in xfs_trans_push_ail().
 */
void
xfs_trans_unlocked_item(
        xfs_mount_t     *mp,
        xfs_log_item_t  *lip)
{
        xfs_log_item_t  *min_lip;

        /*
         * If we're forcibly shutting down, we may have
         * unlocked log items arbitrarily. The last thing
         * we want to do is to move the tail of the log
         * over some potentially valid data.
         */
        if (!(lip->li_flags & XFS_LI_IN_AIL) ||
            XFS_FORCED_SHUTDOWN(mp)) {
                return;
        }

        /*
         * This is the one case where we can call into xfs_ail_min()
         * without holding the AIL lock because we only care about the
         * case where we are at the tail of the AIL.  If the object isn't
         * at the tail, it doesn't matter what result we get back.  This
         * is slightly racy because since we were just unlocked, we could
         * go to sleep between the call to xfs_ail_min and the call to
         * xfs_log_move_tail, have someone else lock us, commit to us disk,
         * move us out of the tail of the AIL, and then we wake up.  However,
         * the call to xfs_log_move_tail() doesn't do anything if there's
         * not enough free space to wake people up so we're safe calling it.
         */
        min_lip = xfs_ail_min(&mp->m_ail.xa_ail);

        if (min_lip == lip)
                xfs_log_move_tail(mp, 1);
}       /* xfs_trans_unlocked_item */


/*
 * Update the position of the item in the AIL with the new
 * lsn.  If it is not yet in the AIL, add it.  Otherwise, move
 * it to its new position by removing it and re-adding it.
 *
 * Wakeup anyone with an lsn less than the item's lsn.  If the item
 * we move in the AIL is the minimum one, update the tail lsn in the
 * log manager.
 *
 * Increment the AIL's generation count to indicate that the tree
 * has changed.
 *
 * This function must be called with the AIL lock held.  The lock
 * is dropped before returning.
 */
void
xfs_trans_update_ail(
        xfs_mount_t     *mp,
        xfs_log_item_t  *lip,
        xfs_lsn_t       lsn) __releases(mp->m_ail_lock)
{
        xfs_ail_entry_t         *ailp;
        xfs_log_item_t          *dlip=NULL;
        xfs_log_item_t          *mlip;  /* ptr to minimum lip */

        ailp = &(mp->m_ail.xa_ail);
        mlip = xfs_ail_min(ailp);

        if (lip->li_flags & XFS_LI_IN_AIL) {
                dlip = xfs_ail_delete(ailp, lip);
                ASSERT(dlip == lip);
        } else {
                lip->li_flags |= XFS_LI_IN_AIL;
        }

        lip->li_lsn = lsn;

        xfs_ail_insert(ailp, lip);
        mp->m_ail.xa_gen++;

        if (mlip == dlip) {
                mlip = xfs_ail_min(&(mp->m_ail.xa_ail));
                spin_unlock(&mp->m_ail_lock);
                xfs_log_move_tail(mp, mlip->li_lsn);
        } else {
                spin_unlock(&mp->m_ail_lock);
        }


}       /* xfs_trans_update_ail */

/*
 * Delete the given item from the AIL.  It must already be in
 * the AIL.
 *
 * Wakeup anyone with an lsn less than item's lsn.    If the item
 * we delete in the AIL is the minimum one, update the tail lsn in the
 * log manager.
 *
 * Clear the IN_AIL flag from the item, reset its lsn to 0, and
 * bump the AIL's generation count to indicate that the tree
 * has changed.
 *
 * This function must be called with the AIL lock held.  The lock
 * is dropped before returning.
 */
void
xfs_trans_delete_ail(
        xfs_mount_t     *mp,
        xfs_log_item_t  *lip) __releases(mp->m_ail_lock)
{
        xfs_ail_entry_t         *ailp;
        xfs_log_item_t          *dlip;
        xfs_log_item_t          *mlip;

        if (lip->li_flags & XFS_LI_IN_AIL) {
                ailp = &(mp->m_ail.xa_ail);
                mlip = xfs_ail_min(ailp);
                dlip = xfs_ail_delete(ailp, lip);
                ASSERT(dlip == lip);


                lip->li_flags &= ~XFS_LI_IN_AIL;
                lip->li_lsn = 0;
                mp->m_ail.xa_gen++;

                if (mlip == dlip) {
                        mlip = xfs_ail_min(&(mp->m_ail.xa_ail));
                        spin_unlock(&mp->m_ail_lock);
                        xfs_log_move_tail(mp, (mlip ? mlip->li_lsn : 0));
                } else {
                        spin_unlock(&mp->m_ail_lock);
                }
        }
        else {
                /*
                 * If the file system is not being shutdown, we are in
                 * serious trouble if we get to this stage.
                 */
                if (XFS_FORCED_SHUTDOWN(mp))
                        spin_unlock(&mp->m_ail_lock);
                else {
                        xfs_cmn_err(XFS_PTAG_AILDELETE, CE_ALERT, mp,
                "%s: attempting to delete a log item that is not in the AIL",
                                        __FUNCTION__);
                        spin_unlock(&mp->m_ail_lock);
                        xfs_force_shutdown(mp, SHUTDOWN_CORRUPT_INCORE);
                }
        }
}



/*
 * Return the item in the AIL with the smallest lsn.
 * Return the current tree generation number for use
 * in calls to xfs_trans_next_ail().
 */
xfs_log_item_t *
xfs_trans_first_ail(
        xfs_mount_t     *mp,
        int             *gen)
{
        xfs_log_item_t  *lip;

        lip = xfs_ail_min(&(mp->m_ail.xa_ail));
        *gen = (int)mp->m_ail.xa_gen;

        return lip;
}

/*
 * If the generation count of the tree has not changed since the
 * caller last took something from the AIL, then return the elmt
 * in the tree which follows the one given.  If the count has changed,
 * then return the minimum elmt of the AIL and bump the restarts counter
 * if one is given.
 */
xfs_log_item_t *
xfs_trans_next_ail(
        xfs_mount_t     *mp,
        xfs_log_item_t  *lip,
        int             *gen,
        int             *restarts)
{
        xfs_log_item_t  *nlip;

        ASSERT(mp && lip && gen);
        if (mp->m_ail.xa_gen == *gen) {
                nlip = xfs_ail_next(&(mp->m_ail.xa_ail), lip);
        } else {
                nlip = xfs_ail_min(&(mp->m_ail).xa_ail);
                *gen = (int)mp->m_ail.xa_gen;
                if (restarts != NULL) {
                        XFS_STATS_INC(xs_push_ail_restarts);
                        (*restarts)++;
                }
        }

        return (nlip);
}


/*
 * The active item list (AIL) is a doubly linked list of log
 * items sorted by ascending lsn.  The base of the list is
 * a forw/back pointer pair embedded in the xfs mount structure.
 * The base is initialized with both pointers pointing to the
 * base.  This case always needs to be distinguished, because
 * the base has no lsn to look at.  We almost always insert
 * at the end of the list, so on inserts we search from the
 * end of the list to find where the new item belongs.
 */

/*
 * Initialize the doubly linked list to point only to itself.
 */
int
xfs_trans_ail_init(
        xfs_mount_t     *mp)
{
        mp->m_ail.xa_ail.ail_forw = (xfs_log_item_t*)&mp->m_ail.xa_ail;
        mp->m_ail.xa_ail.ail_back = (xfs_log_item_t*)&mp->m_ail.xa_ail;
        return xfsaild_start(mp);
}

void
xfs_trans_ail_destroy(
        xfs_mount_t     *mp)
{
        xfsaild_stop(mp);
}

/*
 * Insert the given log item into the AIL.
 * We almost always insert at the end of the list, so on inserts
 * we search from the end of the list to find where the
 * new item belongs.
 */
STATIC void
xfs_ail_insert(
        xfs_ail_entry_t *base,
        xfs_log_item_t  *lip)
/* ARGSUSED */
{
        xfs_log_item_t  *next_lip;

        /*
         * If the list is empty, just insert the item.
         */
        if (base->ail_back == (xfs_log_item_t*)base) {
                base->ail_forw = lip;
                base->ail_back = lip;
                lip->li_ail.ail_forw = (xfs_log_item_t*)base;
                lip->li_ail.ail_back = (xfs_log_item_t*)base;
                return;
        }

        next_lip = base->ail_back;
        while ((next_lip != (xfs_log_item_t*)base) &&
               (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) > 0)) {
                next_lip = next_lip->li_ail.ail_back;
        }
        ASSERT((next_lip == (xfs_log_item_t*)base) ||
               (XFS_LSN_CMP(next_lip->li_lsn, lip->li_lsn) <= 0));
        lip->li_ail.ail_forw = next_lip->li_ail.ail_forw;
        lip->li_ail.ail_back = next_lip;
        next_lip->li_ail.ail_forw = lip;
        lip->li_ail.ail_forw->li_ail.ail_back = lip;

        xfs_ail_check(base, lip);
        return;
}

/*
 * Delete the given item from the AIL.  Return a pointer to the item.
 */
/*ARGSUSED*/
STATIC xfs_log_item_t *
xfs_ail_delete(
        xfs_ail_entry_t *base,
        xfs_log_item_t  *lip)
/* ARGSUSED */
{
        xfs_ail_check(base, lip);
        lip->li_ail.ail_forw->li_ail.ail_back = lip->li_ail.ail_back;
        lip->li_ail.ail_back->li_ail.ail_forw = lip->li_ail.ail_forw;
        lip->li_ail.ail_forw = NULL;
        lip->li_ail.ail_back = NULL;

        return lip;
}

/*
 * Return a pointer to the first item in the AIL.
 * If the AIL is empty, then return NULL.
 */
STATIC xfs_log_item_t *
xfs_ail_min(
        xfs_ail_entry_t *base)
/* ARGSUSED */
{
        register xfs_log_item_t *forw = base->ail_forw;
        if (forw == (xfs_log_item_t*)base) {
                return NULL;
        }
        return forw;
}

/*
 * 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(
        xfs_ail_entry_t *base,
        xfs_log_item_t  *lip)
/* ARGSUSED */
{
        if (lip->li_ail.ail_forw == (xfs_log_item_t*)base) {
                return NULL;
        }
        return lip->li_ail.ail_forw;

}

#ifdef DEBUG
/*
 * Check that the list is sorted as it should be.
 */
STATIC void
xfs_ail_check(
        xfs_ail_entry_t *base,
        xfs_log_item_t  *lip)
{
        xfs_log_item_t  *prev_lip;

        prev_lip = base->ail_forw;
        if (prev_lip == (xfs_log_item_t*)base) {
                /*
                 * Make sure the pointers are correct when the list
                 * is empty.
                 */
                ASSERT(base->ail_back == (xfs_log_item_t*)base);
                return;
        }

        /*
         * Check the next and previous entries are valid.
         */
        ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
        prev_lip = lip->li_ail.ail_back;
        if (prev_lip != (xfs_log_item_t*)base) {
                ASSERT(prev_lip->li_ail.ail_forw == lip);
                ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
        }
        prev_lip = lip->li_ail.ail_forw;
        if (prev_lip != (xfs_log_item_t*)base) {
                ASSERT(prev_lip->li_ail.ail_back == lip);
                ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) >= 0);
        }


#ifdef XFS_TRANS_DEBUG
        /*
         * Walk the list checking forward and backward pointers,
         * lsn ordering, and that every entry has the XFS_LI_IN_AIL
         * flag set. This is really expensive, so only do it when
         * specifically debugging the transaction subsystem.
         */
        prev_lip = (xfs_log_item_t*)base;
        while (lip != (xfs_log_item_t*)base) {
                if (prev_lip != (xfs_log_item_t*)base) {
                        ASSERT(prev_lip->li_ail.ail_forw == lip);
                        ASSERT(XFS_LSN_CMP(prev_lip->li_lsn, lip->li_lsn) <= 0);
                }
                ASSERT(lip->li_ail.ail_back == prev_lip);
                ASSERT((lip->li_flags & XFS_LI_IN_AIL) != 0);
                prev_lip = lip;
                lip = lip->li_ail.ail_forw;
        }
        ASSERT(lip == (xfs_log_item_t*)base);
        ASSERT(base->ail_back == prev_lip);
#endif /* XFS_TRANS_DEBUG */
}
#endif /* DEBUG */