xfs: mark the xfssyncd workqueue as non-reentrant

[~andy/linux] / fs / xfs / xfs_sync.c

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

#include <linux/kthread.h>
#include <linux/freezer.h>

struct workqueue_struct *xfs_syncd_wq;  /* sync workqueue */

/*
 * The inode lookup is done in batches to keep the amount of lock traffic and
 * radix tree lookups to a minimum. The batch size is a trade off between
 * lookup reduction and stack usage. This is in the reclaim path, so we can't
 * be too greedy.
 */
#define XFS_LOOKUP_BATCH        32

STATIC int
xfs_inode_ag_walk_grab(
        struct xfs_inode        *ip)
{
        struct inode            *inode = VFS_I(ip);

        ASSERT(rcu_read_lock_held());

        /*
         * check for stale RCU freed inode
         *
         * If the inode has been reallocated, it doesn't matter if it's not in
         * the AG we are walking - we are walking for writeback, so if it
         * passes all the "valid inode" checks and is dirty, then we'll write
         * it back anyway.  If it has been reallocated and still being
         * initialised, the XFS_INEW check below will catch it.
         */
        spin_lock(&ip->i_flags_lock);
        if (!ip->i_ino)
                goto out_unlock_noent;

        /* avoid new or reclaimable inodes. Leave for reclaim code to flush */
        if (__xfs_iflags_test(ip, XFS_INEW | XFS_IRECLAIMABLE | XFS_IRECLAIM))
                goto out_unlock_noent;
        spin_unlock(&ip->i_flags_lock);

        /* nothing to sync during shutdown */
        if (XFS_FORCED_SHUTDOWN(ip->i_mount))
                return EFSCORRUPTED;

        /* If we can't grab the inode, it must on it's way to reclaim. */
        if (!igrab(inode))
                return ENOENT;

        if (is_bad_inode(inode)) {
                IRELE(ip);
                return ENOENT;
        }

        /* inode is valid */
        return 0;

out_unlock_noent:
        spin_unlock(&ip->i_flags_lock);
        return ENOENT;
}

STATIC int
xfs_inode_ag_walk(
        struct xfs_mount        *mp,
        struct xfs_perag        *pag,
        int                     (*execute)(struct xfs_inode *ip,
                                           struct xfs_perag *pag, int flags),
        int                     flags)
{
        uint32_t                first_index;
        int                     last_error = 0;
        int                     skipped;
        int                     done;
        int                     nr_found;

restart:
        done = 0;
        skipped = 0;
        first_index = 0;
        nr_found = 0;
        do {
                struct xfs_inode *batch[XFS_LOOKUP_BATCH];
                int             error = 0;
                int             i;

                rcu_read_lock();
                nr_found = radix_tree_gang_lookup(&pag->pag_ici_root,
                                        (void **)batch, first_index,
                                        XFS_LOOKUP_BATCH);
                if (!nr_found) {
                        rcu_read_unlock();
                        break;
                }

                /*
                 * Grab the inodes before we drop the lock. if we found
                 * nothing, nr == 0 and the loop will be skipped.
                 */
                for (i = 0; i < nr_found; i++) {
                        struct xfs_inode *ip = batch[i];

                        if (done || xfs_inode_ag_walk_grab(ip))
                                batch[i] = NULL;

                        /*
                         * Update the index for the next lookup. Catch
                         * overflows into the next AG range which can occur if
                         * we have inodes in the last block of the AG and we
                         * are currently pointing to the last inode.
                         *
                         * Because we may see inodes that are from the wrong AG
                         * due to RCU freeing and reallocation, only update the
                         * index if it lies in this AG. It was a race that lead
                         * us to see this inode, so another lookup from the
                         * same index will not find it again.
                         */
                        if (XFS_INO_TO_AGNO(mp, ip->i_ino) != pag->pag_agno)
                                continue;
                        first_index = XFS_INO_TO_AGINO(mp, ip->i_ino + 1);
                        if (first_index < XFS_INO_TO_AGINO(mp, ip->i_ino))
                                done = 1;
                }

                /* unlock now we've grabbed the inodes. */
                rcu_read_unlock();

                for (i = 0; i < nr_found; i++) {
                        if (!batch[i])
                                continue;
                        error = execute(batch[i], pag, flags);
                        IRELE(batch[i]);
                        if (error == EAGAIN) {
                                skipped++;
                                continue;
                        }
                        if (error && last_error != EFSCORRUPTED)
                                last_error = error;
                }

                /* bail out if the filesystem is corrupted.  */
                if (error == EFSCORRUPTED)
                        break;

                cond_resched();

        } while (nr_found && !done);

        if (skipped) {
                delay(1);
                goto restart;
        }
        return last_error;
}

int
xfs_inode_ag_iterator(
        struct xfs_mount        *mp,
        int                     (*execute)(struct xfs_inode *ip,
                                           struct xfs_perag *pag, int flags),
        int                     flags)
{
        struct xfs_perag        *pag;
        int                     error = 0;
        int                     last_error = 0;
        xfs_agnumber_t          ag;

        ag = 0;
        while ((pag = xfs_perag_get(mp, ag))) {
                ag = pag->pag_agno + 1;
                error = xfs_inode_ag_walk(mp, pag, execute, flags);
                xfs_perag_put(pag);
                if (error) {
                        last_error = error;
                        if (error == EFSCORRUPTED)
                                break;
                }
        }
        return XFS_ERROR(last_error);
}

STATIC int
xfs_sync_inode_data(
        struct xfs_inode        *ip,
        struct xfs_perag        *pag,
        int                     flags)
{
        struct inode            *inode = VFS_I(ip);
        struct address_space *mapping = inode->i_mapping;
        int                     error = 0;

        if (!mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
                return 0;

        if (!xfs_ilock_nowait(ip, XFS_IOLOCK_SHARED)) {
                if (flags & SYNC_TRYLOCK)
                        return 0;
                xfs_ilock(ip, XFS_IOLOCK_SHARED);
        }

        error = xfs_flush_pages(ip, 0, -1, (flags & SYNC_WAIT) ?
                                0 : XBF_ASYNC, FI_NONE);
        xfs_iunlock(ip, XFS_IOLOCK_SHARED);
        return error;
}

STATIC int
xfs_sync_inode_attr(
        struct xfs_inode        *ip,
        struct xfs_perag        *pag,
        int                     flags)
{
        int                     error = 0;

        xfs_ilock(ip, XFS_ILOCK_SHARED);
        if (xfs_inode_clean(ip))
                goto out_unlock;
        if (!xfs_iflock_nowait(ip)) {
                if (!(flags & SYNC_WAIT))
                        goto out_unlock;
                xfs_iflock(ip);
        }

        if (xfs_inode_clean(ip)) {
                xfs_ifunlock(ip);
                goto out_unlock;
        }

        error = xfs_iflush(ip, flags);

        /*
         * We don't want to try again on non-blocking flushes that can't run
         * again immediately. If an inode really must be written, then that's
         * what the SYNC_WAIT flag is for.
         */
        if (error == EAGAIN) {
                ASSERT(!(flags & SYNC_WAIT));
                error = 0;
        }

 out_unlock:
        xfs_iunlock(ip, XFS_ILOCK_SHARED);
        return error;
}

/*
 * Write out pagecache data for the whole filesystem.
 */
STATIC int
xfs_sync_data(
        struct xfs_mount        *mp,
        int                     flags)
{
        int                     error;

        ASSERT((flags & ~(SYNC_TRYLOCK|SYNC_WAIT)) == 0);

        error = xfs_inode_ag_iterator(mp, xfs_sync_inode_data, flags);
        if (error)
                return XFS_ERROR(error);

        xfs_log_force(mp, (flags & SYNC_WAIT) ? XFS_LOG_SYNC : 0);
        return 0;
}

/*
 * Write out inode metadata (attributes) for the whole filesystem.
 */
STATIC int
xfs_sync_attr(
        struct xfs_mount        *mp,
        int                     flags)
{
        ASSERT((flags & ~SYNC_WAIT) == 0);

        return xfs_inode_ag_iterator(mp, xfs_sync_inode_attr, flags);
}

STATIC int
xfs_sync_fsdata(
        struct xfs_mount        *mp)
{
        struct xfs_buf          *bp;
        int                     error;

        /*
         * If the buffer is pinned then push on the log so we won't get stuck
         * waiting in the write for someone, maybe ourselves, to flush the log.
         *
         * Even though we just pushed the log above, we did not have the
         * superblock buffer locked at that point so it can become pinned in
         * between there and here.
         */
        bp = xfs_getsb(mp, 0);
        if (xfs_buf_ispinned(bp))
                xfs_log_force(mp, 0);
        error = xfs_bwrite(bp);
        xfs_buf_relse(bp);
        return error;
}

/*
 * When remounting a filesystem read-only or freezing the filesystem, we have
 * two phases to execute. This first phase is syncing the data before we
 * quiesce the filesystem, and the second is flushing all the inodes out after
 * we've waited for all the transactions created by the first phase to
 * complete. The second phase ensures that the inodes are written to their
 * location on disk rather than just existing in transactions in the log. This
 * means after a quiesce there is no log replay required to write the inodes to
 * disk (this is the main difference between a sync and a quiesce).
 */
/*
 * First stage of freeze - no writers will make progress now we are here,
 * so we flush delwri and delalloc buffers here, then wait for all I/O to
 * complete.  Data is frozen at that point. Metadata is not frozen,
 * transactions can still occur here so don't bother flushing the buftarg
 * because it'll just get dirty again.
 */
int
xfs_quiesce_data(
        struct xfs_mount        *mp)
{
        int                     error, error2 = 0;

        /* force out the log */
        xfs_log_force(mp, XFS_LOG_SYNC);

        /* write superblock and hoover up shutdown errors */
        error = xfs_sync_fsdata(mp);

        /* make sure all delwri buffers are written out */
        xfs_flush_buftarg(mp->m_ddev_targp, 1);

        /* mark the log as covered if needed */
        if (xfs_log_need_covered(mp))
                error2 = xfs_fs_log_dummy(mp);

        /* flush data-only devices */
        if (mp->m_rtdev_targp)
                xfs_flush_buftarg(mp->m_rtdev_targp, 1);

        return error ? error : error2;
}

STATIC void
xfs_quiesce_fs(
        struct xfs_mount        *mp)
{
        int     count = 0, pincount;

        xfs_reclaim_inodes(mp, 0);
        xfs_flush_buftarg(mp->m_ddev_targp, 0);

        /*
         * This loop must run at least twice.  The first instance of the loop
         * will flush most meta data but that will generate more meta data
         * (typically directory updates).  Which then must be flushed and
         * logged before we can write the unmount record. We also so sync
         * reclaim of inodes to catch any that the above delwri flush skipped.
         */
        do {
                xfs_reclaim_inodes(mp, SYNC_WAIT);
                xfs_sync_attr(mp, SYNC_WAIT);
                pincount = xfs_flush_buftarg(mp->m_ddev_targp, 1);
                if (!pincount) {
                        delay(50);
                        count++;
                }
        } while (count < 2);
}

/*
 * Second stage of a quiesce. The data is already synced, now we have to take
 * care of the metadata. New transactions are already blocked, so we need to
 * wait for any remaining transactions to drain out before proceeding.
 */
void
xfs_quiesce_attr(
        struct xfs_mount        *mp)
{
        int     error = 0;

        /* wait for all modifications to complete */
        while (atomic_read(&mp->m_active_trans) > 0)
                delay(100);

        /* flush inodes and push all remaining buffers out to disk */
        xfs_quiesce_fs(mp);

        /*
         * Just warn here till VFS can correctly support
         * read-only remount without racing.
         */
        WARN_ON(atomic_read(&mp->m_active_trans) != 0);

        /* Push the superblock and write an unmount record */
        error = xfs_log_sbcount(mp);
        if (error)
                xfs_warn(mp, "xfs_attr_quiesce: failed to log sb changes. "
                                "Frozen image may not be consistent.");
        xfs_log_unmount_write(mp);
        xfs_unmountfs_writesb(mp);
}

static void
xfs_syncd_queue_sync(
        struct xfs_mount        *mp)
{
        queue_delayed_work(xfs_syncd_wq, &mp->m_sync_work,
                                msecs_to_jiffies(xfs_syncd_centisecs * 10));
}

/*
 * Every sync period we need to unpin all items, reclaim inodes and sync
 * disk quotas.  We might need to cover the log to indicate that the
 * filesystem is idle and not frozen.
 */
STATIC void
xfs_sync_worker(
        struct work_struct *work)
{
        struct xfs_mount *mp = container_of(to_delayed_work(work),
                                        struct xfs_mount, m_sync_work);
        int             error;

        if (!(mp->m_flags & XFS_MOUNT_RDONLY)) {
                /* dgc: errors ignored here */
                if (mp->m_super->s_frozen == SB_UNFROZEN &&
                    xfs_log_need_covered(mp))
                        error = xfs_fs_log_dummy(mp);
                else
                        xfs_log_force(mp, 0);

                /* start pushing all the metadata that is currently dirty */
                xfs_ail_push_all(mp->m_ail);
        }

        /* queue us up again */
        xfs_syncd_queue_sync(mp);
}

/*
 * Queue a new inode reclaim pass if there are reclaimable inodes and there
 * isn't a reclaim pass already in progress. By default it runs every 5s based
 * on the xfs syncd work default of 30s. Perhaps this should have it's own
 * tunable, but that can be done if this method proves to be ineffective or too
 * aggressive.
 */
static void
xfs_syncd_queue_reclaim(
        struct xfs_mount        *mp)
{

        /*
         * We can have inodes enter reclaim after we've shut down the syncd
         * workqueue during unmount, so don't allow reclaim work to be queued
         * during unmount.
         */
        if (!(mp->m_super->s_flags & MS_ACTIVE))
                return;

        rcu_read_lock();
        if (radix_tree_tagged(&mp->m_perag_tree, XFS_ICI_RECLAIM_TAG)) {
                queue_delayed_work(xfs_syncd_wq, &mp->m_reclaim_work,
                        msecs_to_jiffies(xfs_syncd_centisecs / 6 * 10));
        }
        rcu_read_unlock();
}

/*
 * This is a fast pass over the inode cache to try to get reclaim moving on as
 * many inodes as possible in a short period of time. It kicks itself every few
 * seconds, as well as being kicked by the inode cache shrinker when memory
 * goes low. It scans as quickly as possible avoiding locked inodes or those
 * already being flushed, and once done schedules a future pass.
 */
STATIC void
xfs_reclaim_worker(
        struct work_struct *work)
{
        struct xfs_mount *mp = container_of(to_delayed_work(work),
                                        struct xfs_mount, m_reclaim_work);

        xfs_reclaim_inodes(mp, SYNC_TRYLOCK);
        xfs_syncd_queue_reclaim(mp);
}

/*
 * Flush delayed allocate data, attempting to free up reserved space
 * from existing allocations.  At this point a new allocation attempt
 * has failed with ENOSPC and we are in the process of scratching our
 * heads, looking about for more room.
 *
 * Queue a new data flush if there isn't one already in progress and
 * wait for completion of the flush. This means that we only ever have one
 * inode flush in progress no matter how many ENOSPC events are occurring and
 * so will prevent the system from bogging down due to every concurrent
 * ENOSPC event scanning all the active inodes in the system for writeback.
 */
void
xfs_flush_inodes(
        struct xfs_inode        *ip)
{
        struct xfs_mount        *mp = ip->i_mount;

        queue_work(xfs_syncd_wq, &mp->m_flush_work);
        flush_work_sync(&mp->m_flush_work);
}

STATIC void
xfs_flush_worker(
        struct work_struct *work)
{
        struct xfs_mount *mp = container_of(work,
                                        struct xfs_mount, m_flush_work);

        xfs_sync_data(mp, SYNC_TRYLOCK);
        xfs_sync_data(mp, SYNC_TRYLOCK | SYNC_WAIT);
}

int
xfs_syncd_init(
        struct xfs_mount        *mp)
{
        INIT_WORK(&mp->m_flush_work, xfs_flush_worker);
        INIT_DELAYED_WORK(&mp->m_sync_work, xfs_sync_worker);
        INIT_DELAYED_WORK(&mp->m_reclaim_work, xfs_reclaim_worker);

        xfs_syncd_queue_sync(mp);
        xfs_syncd_queue_reclaim(mp);

        return 0;
}

void
xfs_syncd_stop(
        struct xfs_mount        *mp)
{
        cancel_delayed_work_sync(&mp->m_sync_work);
        cancel_delayed_work_sync(&mp->m_reclaim_work);
        cancel_work_sync(&mp->m_flush_work);
}

void
__xfs_inode_set_reclaim_tag(
        struct xfs_perag        *pag,
        struct xfs_inode        *ip)
{
        radix_tree_tag_set(&pag->pag_ici_root,
                           XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino),
                           XFS_ICI_RECLAIM_TAG);

        if (!pag->pag_ici_reclaimable) {
                /* propagate the reclaim tag up into the perag radix tree */
                spin_lock(&ip->i_mount->m_perag_lock);
                radix_tree_tag_set(&ip->i_mount->m_perag_tree,
                                XFS_INO_TO_AGNO(ip->i_mount, ip->i_ino),
                                XFS_ICI_RECLAIM_TAG);
                spin_unlock(&ip->i_mount->m_perag_lock);

                /* schedule periodic background inode reclaim */
                xfs_syncd_queue_reclaim(ip->i_mount);

                trace_xfs_perag_set_reclaim(ip->i_mount, pag->pag_agno,
                                                        -1, _RET_IP_);
        }
        pag->pag_ici_reclaimable++;
}

/*
 * We set the inode flag atomically with the radix tree tag.
 * Once we get tag lookups on the radix tree, this inode flag
 * can go away.
 */
void
xfs_inode_set_reclaim_tag(
        xfs_inode_t     *ip)
{
        struct xfs_mount *mp = ip->i_mount;
        struct xfs_perag *pag;

        pag = xfs_perag_get(mp, XFS_INO_TO_AGNO(mp, ip->i_ino));
        spin_lock(&pag->pag_ici_lock);
        spin_lock(&ip->i_flags_lock);
        __xfs_inode_set_reclaim_tag(pag, ip);
        __xfs_iflags_set(ip, XFS_IRECLAIMABLE);
        spin_unlock(&ip->i_flags_lock);
        spin_unlock(&pag->pag_ici_lock);
        xfs_perag_put(pag);
}

STATIC void
__xfs_inode_clear_reclaim(
        xfs_perag_t     *pag,
        xfs_inode_t     *ip)
{
        pag->pag_ici_reclaimable--;
        if (!pag->pag_ici_reclaimable) {
                /* clear the reclaim tag from the perag radix tree */
                spin_lock(&ip->i_mount->m_perag_lock);
                radix_tree_tag_clear(&ip->i_mount->m_perag_tree,
                                XFS_INO_TO_AGNO(ip->i_mount, ip->i_ino),
                                XFS_ICI_RECLAIM_TAG);
                spin_unlock(&ip->i_mount->m_perag_lock);
                trace_xfs_perag_clear_reclaim(ip->i_mount, pag->pag_agno,
                                                        -1, _RET_IP_);
        }
}

void
__xfs_inode_clear_reclaim_tag(
        xfs_mount_t     *mp,
        xfs_perag_t     *pag,
        xfs_inode_t     *ip)
{
        radix_tree_tag_clear(&pag->pag_ici_root,
                        XFS_INO_TO_AGINO(mp, ip->i_ino), XFS_ICI_RECLAIM_TAG);
        __xfs_inode_clear_reclaim(pag, ip);
}

/*
 * Grab the inode for reclaim exclusively.
 * Return 0 if we grabbed it, non-zero otherwise.
 */
STATIC int
xfs_reclaim_inode_grab(
        struct xfs_inode        *ip,
        int                     flags)
{
        ASSERT(rcu_read_lock_held());

        /* quick check for stale RCU freed inode */
        if (!ip->i_ino)
                return 1;

        /*
         * do some unlocked checks first to avoid unnecessary lock traffic.
         * The first is a flush lock check, the second is a already in reclaim
         * check. Only do these checks if we are not going to block on locks.
         */
        if ((flags & SYNC_TRYLOCK) &&
            (!ip->i_flush.done || __xfs_iflags_test(ip, XFS_IRECLAIM))) {
                return 1;
        }

        /*
         * The radix tree lock here protects a thread in xfs_iget from racing
         * with us starting reclaim on the inode.  Once we have the
         * XFS_IRECLAIM flag set it will not touch us.
         *
         * Due to RCU lookup, we may find inodes that have been freed and only
         * have XFS_IRECLAIM set.  Indeed, we may see reallocated inodes that
         * aren't candidates for reclaim at all, so we must check the
         * XFS_IRECLAIMABLE is set first before proceeding to reclaim.
         */
        spin_lock(&ip->i_flags_lock);
        if (!__xfs_iflags_test(ip, XFS_IRECLAIMABLE) ||
            __xfs_iflags_test(ip, XFS_IRECLAIM)) {
                /* not a reclaim candidate. */
                spin_unlock(&ip->i_flags_lock);
                return 1;
        }
        __xfs_iflags_set(ip, XFS_IRECLAIM);
        spin_unlock(&ip->i_flags_lock);
        return 0;
}

/*
 * Inodes in different states need to be treated differently, and the return
 * value of xfs_iflush is not sufficient to get this right. The following table
 * lists the inode states and the reclaim actions necessary for non-blocking
 * reclaim:
 *
 *
 *      inode state          iflush ret         required action
 *      ---------------      ----------         ---------------
 *      bad                     -               reclaim
 *      shutdown                EIO             unpin and reclaim
 *      clean, unpinned         0               reclaim
 *      stale, unpinned         0               reclaim
 *      clean, pinned(*)        0               requeue
 *      stale, pinned           EAGAIN          requeue
 *      dirty, delwri ok        0               requeue
 *      dirty, delwri blocked   EAGAIN          requeue
 *      dirty, sync flush       0               reclaim
 *
 * (*) dgc: I don't think the clean, pinned state is possible but it gets
 * handled anyway given the order of checks implemented.
 *
 * As can be seen from the table, the return value of xfs_iflush() is not
 * sufficient to correctly decide the reclaim action here. The checks in
 * xfs_iflush() might look like duplicates, but they are not.
 *
 * Also, because we get the flush lock first, we know that any inode that has
 * been flushed delwri has had the flush completed by the time we check that
 * the inode is clean. The clean inode check needs to be done before flushing
 * the inode delwri otherwise we would loop forever requeuing clean inodes as
 * we cannot tell apart a successful delwri flush and a clean inode from the
 * return value of xfs_iflush().
 *
 * Note that because the inode is flushed delayed write by background
 * writeback, the flush lock may already be held here and waiting on it can
 * result in very long latencies. Hence for sync reclaims, where we wait on the
 * flush lock, the caller should push out delayed write inodes first before
 * trying to reclaim them to minimise the amount of time spent waiting. For
 * background relaim, we just requeue the inode for the next pass.
 *
 * Hence the order of actions after gaining the locks should be:
 *      bad             => reclaim
 *      shutdown        => unpin and reclaim
 *      pinned, delwri  => requeue
 *      pinned, sync    => unpin
 *      stale           => reclaim
 *      clean           => reclaim
 *      dirty, delwri   => flush and requeue
 *      dirty, sync     => flush, wait and reclaim
 */
STATIC int
xfs_reclaim_inode(
        struct xfs_inode        *ip,
        struct xfs_perag        *pag,
        int                     sync_mode)
{
        int     error;

restart:
        error = 0;
        xfs_ilock(ip, XFS_ILOCK_EXCL);
        if (!xfs_iflock_nowait(ip)) {
                if (!(sync_mode & SYNC_WAIT))
                        goto out;

                /*
                 * If we only have a single dirty inode in a cluster there is
                 * a fair chance that the AIL push may have pushed it into
                 * the buffer, but xfsbufd won't touch it until 30 seconds
                 * from now, and thus we will lock up here.
                 *
                 * Promote the inode buffer to the front of the delwri list
                 * and wake up xfsbufd now.
                 */
                xfs_promote_inode(ip);
                xfs_iflock(ip);
        }

        if (is_bad_inode(VFS_I(ip)))
                goto reclaim;
        if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                xfs_iunpin_wait(ip);
                goto reclaim;
        }
        if (xfs_ipincount(ip)) {
                if (!(sync_mode & SYNC_WAIT)) {
                        xfs_ifunlock(ip);
                        goto out;
                }
                xfs_iunpin_wait(ip);
        }
        if (xfs_iflags_test(ip, XFS_ISTALE))
                goto reclaim;
        if (xfs_inode_clean(ip))
                goto reclaim;

        /*
         * Now we have an inode that needs flushing.
         *
         * We do a nonblocking flush here even if we are doing a SYNC_WAIT
         * reclaim as we can deadlock with inode cluster removal.
         * xfs_ifree_cluster() can lock the inode buffer before it locks the
         * ip->i_lock, and we are doing the exact opposite here. As a result,
         * doing a blocking xfs_itobp() to get the cluster buffer will result
         * in an ABBA deadlock with xfs_ifree_cluster().
         *
         * As xfs_ifree_cluser() must gather all inodes that are active in the
         * cache to mark them stale, if we hit this case we don't actually want
         * to do IO here - we want the inode marked stale so we can simply
         * reclaim it. Hence if we get an EAGAIN error on a SYNC_WAIT flush,
         * just unlock the inode, back off and try again. Hopefully the next
         * pass through will see the stale flag set on the inode.
         */
        error = xfs_iflush(ip, SYNC_TRYLOCK | sync_mode);
        if (sync_mode & SYNC_WAIT) {
                if (error == EAGAIN) {
                        xfs_iunlock(ip, XFS_ILOCK_EXCL);
                        /* backoff longer than in xfs_ifree_cluster */
                        delay(2);
                        goto restart;
                }
                xfs_iflock(ip);
                goto reclaim;
        }

        /*
         * When we have to flush an inode but don't have SYNC_WAIT set, we
         * flush the inode out using a delwri buffer and wait for the next
         * call into reclaim to find it in a clean state instead of waiting for
         * it now. We also don't return errors here - if the error is transient
         * then the next reclaim pass will flush the inode, and if the error
         * is permanent then the next sync reclaim will reclaim the inode and
         * pass on the error.
         */
        if (error && error != EAGAIN && !XFS_FORCED_SHUTDOWN(ip->i_mount)) {
                xfs_warn(ip->i_mount,
                        "inode 0x%llx background reclaim flush failed with %d",
                        (long long)ip->i_ino, error);
        }
out:
        xfs_iflags_clear(ip, XFS_IRECLAIM);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);
        /*
         * We could return EAGAIN here to make reclaim rescan the inode tree in
         * a short while. However, this just burns CPU time scanning the tree
         * waiting for IO to complete and xfssyncd never goes back to the idle
         * state. Instead, return 0 to let the next scheduled background reclaim
         * attempt to reclaim the inode again.
         */
        return 0;

reclaim:
        xfs_ifunlock(ip);
        xfs_iunlock(ip, XFS_ILOCK_EXCL);

        XFS_STATS_INC(xs_ig_reclaims);
        /*
         * Remove the inode from the per-AG radix tree.
         *
         * Because radix_tree_delete won't complain even if the item was never
         * added to the tree assert that it's been there before to catch
         * problems with the inode life time early on.
         */
        spin_lock(&pag->pag_ici_lock);
        if (!radix_tree_delete(&pag->pag_ici_root,
                                XFS_INO_TO_AGINO(ip->i_mount, ip->i_ino)))
                ASSERT(0);
        __xfs_inode_clear_reclaim(pag, ip);
        spin_unlock(&pag->pag_ici_lock);

        /*
         * Here we do an (almost) spurious inode lock in order to coordinate
         * with inode cache radix tree lookups.  This is because the lookup
         * can reference the inodes in the cache without taking references.
         *
         * We make that OK here by ensuring that we wait until the inode is
         * unlocked after the lookup before we go ahead and free it.  We get
         * both the ilock and the iolock because the code may need to drop the
         * ilock one but will still hold the iolock.
         */
        xfs_ilock(ip, XFS_ILOCK_EXCL | XFS_IOLOCK_EXCL);
        xfs_qm_dqdetach(ip);
        xfs_iunlock(ip, XFS_ILOCK_EXCL | XFS_IOLOCK_EXCL);

        xfs_inode_free(ip);
        return error;

}

/*
 * Walk the AGs and reclaim the inodes in them. Even if the filesystem is
 * corrupted, we still want to try to reclaim all the inodes. If we don't,
 * then a shut down during filesystem unmount reclaim walk leak all the
 * unreclaimed inodes.
 */
int
xfs_reclaim_inodes_ag(
        struct xfs_mount        *mp,
        int                     flags,
        int                     *nr_to_scan)
{
        struct xfs_perag        *pag;
        int                     error = 0;
        int                     last_error = 0;
        xfs_agnumber_t          ag;
        int                     trylock = flags & SYNC_TRYLOCK;
        int                     skipped;

restart:
        ag = 0;
        skipped = 0;
        while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
                unsigned long   first_index = 0;
                int             done = 0;
                int             nr_found = 0;

                ag = pag->pag_agno + 1;

                if (trylock) {
                        if (!mutex_trylock(&pag->pag_ici_reclaim_lock)) {
                                skipped++;
                                xfs_perag_put(pag);
                                continue;
                        }
                        first_index = pag->pag_ici_reclaim_cursor;
                } else
                        mutex_lock(&pag->pag_ici_reclaim_lock);

                do {
                        struct xfs_inode *batch[XFS_LOOKUP_BATCH];
                        int     i;

                        rcu_read_lock();
                        nr_found = radix_tree_gang_lookup_tag(
                                        &pag->pag_ici_root,
                                        (void **)batch, first_index,
                                        XFS_LOOKUP_BATCH,
                                        XFS_ICI_RECLAIM_TAG);
                        if (!nr_found) {
                                done = 1;
                                rcu_read_unlock();
                                break;
                        }

                        /*
                         * Grab the inodes before we drop the lock. if we found
                         * nothing, nr == 0 and the loop will be skipped.
                         */
                        for (i = 0; i < nr_found; i++) {
                                struct xfs_inode *ip = batch[i];

                                if (done || xfs_reclaim_inode_grab(ip, flags))
                                        batch[i] = NULL;

                                /*
                                 * Update the index for the next lookup. Catch
                                 * overflows into the next AG range which can
                                 * occur if we have inodes in the last block of
                                 * the AG and we are currently pointing to the
                                 * last inode.
                                 *
                                 * Because we may see inodes that are from the
                                 * wrong AG due to RCU freeing and
                                 * reallocation, only update the index if it
                                 * lies in this AG. It was a race that lead us
                                 * to see this inode, so another lookup from
                                 * the same index will not find it again.
                                 */
                                if (XFS_INO_TO_AGNO(mp, ip->i_ino) !=
                                                                pag->pag_agno)
                                        continue;
                                first_index = XFS_INO_TO_AGINO(mp, ip->i_ino + 1);
                                if (first_index < XFS_INO_TO_AGINO(mp, ip->i_ino))
                                        done = 1;
                        }

                        /* unlock now we've grabbed the inodes. */
                        rcu_read_unlock();

                        for (i = 0; i < nr_found; i++) {
                                if (!batch[i])
                                        continue;
                                error = xfs_reclaim_inode(batch[i], pag, flags);
                                if (error && last_error != EFSCORRUPTED)
                                        last_error = error;
                        }

                        *nr_to_scan -= XFS_LOOKUP_BATCH;

                        cond_resched();

                } while (nr_found && !done && *nr_to_scan > 0);

                if (trylock && !done)
                        pag->pag_ici_reclaim_cursor = first_index;
                else
                        pag->pag_ici_reclaim_cursor = 0;
                mutex_unlock(&pag->pag_ici_reclaim_lock);
                xfs_perag_put(pag);
        }

        /*
         * if we skipped any AG, and we still have scan count remaining, do
         * another pass this time using blocking reclaim semantics (i.e
         * waiting on the reclaim locks and ignoring the reclaim cursors). This
         * ensure that when we get more reclaimers than AGs we block rather
         * than spin trying to execute reclaim.
         */
        if (skipped && (flags & SYNC_WAIT) && *nr_to_scan > 0) {
                trylock = 0;
                goto restart;
        }
        return XFS_ERROR(last_error);
}

int
xfs_reclaim_inodes(
        xfs_mount_t     *mp,
        int             mode)
{
        int             nr_to_scan = INT_MAX;

        return xfs_reclaim_inodes_ag(mp, mode, &nr_to_scan);
}

/*
 * Scan a certain number of inodes for reclaim.
 *
 * When called we make sure that there is a background (fast) inode reclaim in
 * progress, while we will throttle the speed of reclaim via doing synchronous
 * reclaim of inodes. That means if we come across dirty inodes, we wait for
 * them to be cleaned, which we hope will not be very long due to the
 * background walker having already kicked the IO off on those dirty inodes.
 */
void
xfs_reclaim_inodes_nr(
        struct xfs_mount        *mp,
        int                     nr_to_scan)
{
        /* kick background reclaimer and push the AIL */
        xfs_syncd_queue_reclaim(mp);
        xfs_ail_push_all(mp->m_ail);

        xfs_reclaim_inodes_ag(mp, SYNC_TRYLOCK | SYNC_WAIT, &nr_to_scan);
}

/*
 * Return the number of reclaimable inodes in the filesystem for
 * the shrinker to determine how much to reclaim.
 */
int
xfs_reclaim_inodes_count(
        struct xfs_mount        *mp)
{
        struct xfs_perag        *pag;
        xfs_agnumber_t          ag = 0;
        int                     reclaimable = 0;

        while ((pag = xfs_perag_get_tag(mp, ag, XFS_ICI_RECLAIM_TAG))) {
                ag = pag->pag_agno + 1;
                reclaimable += pag->pag_ici_reclaimable;
                xfs_perag_put(pag);
        }
        return reclaimable;
}