checkpoint.c

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/*
 * linux/fs/jbd2/checkpoint.c
 *
 * Written by Stephen C. Tweedie <[email protected]>, 1999
 *
 * Copyright 1999 Red Hat Software --- All Rights Reserved
 *
 * This file is part of the Linux kernel and is made available under
 * the terms of the GNU General Public License, version 2, or at your
 * option, any later version, incorporated herein by reference.
 *
 * Checkpoint routines for the generic filesystem journaling code.
 * Part of the ext2fs journaling system.
 *
 * Checkpointing is the process of ensuring that a section of the log is
 * committed fully to disk, so that that portion of the log can be
 * reused.
 */

#include <linux/time.h>
#include <linux/fs.h>
#include <linux/jbd2.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <trace/events/jbd2.h>

/*
 * Unlink a buffer from a transaction checkpoint list.
 *
 * Called with j_list_lock held.
 */
static inline void __buffer_unlink_first(struct journal_head *jh)
{
    transaction_t *transaction = jh->b_cp_transaction;

    jh->b_cpnext->b_cpprev = jh->b_cpprev;
    jh->b_cpprev->b_cpnext = jh->b_cpnext;
    if (transaction->t_checkpoint_list == jh) {
        transaction->t_checkpoint_list = jh->b_cpnext;
        if (transaction->t_checkpoint_list == jh)
            transaction->t_checkpoint_list = NULL;
    }
}

/*
 * Unlink a buffer from a transaction checkpoint(io) list.
 *
 * Called with j_list_lock held.
 */
static inline void __buffer_unlink(struct journal_head *jh)
{
    transaction_t *transaction = jh->b_cp_transaction;

    __buffer_unlink_first(jh);
    if (transaction->t_checkpoint_io_list == jh) {
        transaction->t_checkpoint_io_list = jh->b_cpnext;
        if (transaction->t_checkpoint_io_list == jh)
            transaction->t_checkpoint_io_list = NULL;
    }
}

/*
 * Move a buffer from the checkpoint list to the checkpoint io list
 *
 * Called with j_list_lock held
 */
static inline void __buffer_relink_io(struct journal_head *jh)
{
    transaction_t *transaction = jh->b_cp_transaction;

    __buffer_unlink_first(jh);

    if (!transaction->t_checkpoint_io_list) {
        jh->b_cpnext = jh->b_cpprev = jh;
    } else {
        jh->b_cpnext = transaction->t_checkpoint_io_list;
        jh->b_cpprev = transaction->t_checkpoint_io_list->b_cpprev;
        jh->b_cpprev->b_cpnext = jh;
        jh->b_cpnext->b_cpprev = jh;
    }
    transaction->t_checkpoint_io_list = jh;
}

/*
 * Try to release a checkpointed buffer from its transaction.
 * Returns 1 if we released it and 2 if we also released the
 * whole transaction.
 *
 * Requires j_list_lock
 */
static int __try_to_free_cp_buf(struct journal_head *jh)
{
    int ret = 0;
    struct buffer_head *bh = jh2bh(jh);

    if (jh->b_transaction == NULL && !buffer_locked(bh) &&
        !buffer_dirty(bh) && !buffer_write_io_error(bh)) {
        /*
         * Get our reference so that bh cannot be freed before
         * we unlock it
         */
        get_bh(bh);
        JBUFFER_TRACE(jh, "remove from checkpoint list");
        ret = __jbd2_journal_remove_checkpoint(jh) + 1;
        BUFFER_TRACE(bh, "release");
        __brelse(bh);
    }
    return ret;
}

/*
 * __jbd2_log_wait_for_space: wait until there is space in the journal.
 *
 * Called under j-state_lock *only*.  It will be unlocked if we have to wait
 * for a checkpoint to free up some space in the log.
 */
void __jbd2_log_wait_for_space(journal_t *journal)
{
    int nblocks, space_left;
    /* assert_spin_locked(&journal->j_state_lock); */

    nblocks = jbd_space_needed(journal);
    while (__jbd2_log_space_left(journal) < nblocks) {
        if (journal->j_flags & JBD2_ABORT)
            return;
        write_unlock(&journal->j_state_lock);
        mutex_lock(&journal->j_checkpoint_mutex);

        /*
         * Test again, another process may have checkpointed while we
         * were waiting for the checkpoint lock. If there are no
         * transactions ready to be checkpointed, try to recover
         * journal space by calling cleanup_journal_tail(), and if
         * that doesn't work, by waiting for the currently committing
         * transaction to complete.  If there is absolutely no way
         * to make progress, this is either a BUG or corrupted
         * filesystem, so abort the journal and leave a stack
         * trace for forensic evidence.
         */
        write_lock(&journal->j_state_lock);
        spin_lock(&journal->j_list_lock);
        nblocks = jbd_space_needed(journal);
        space_left = __jbd2_log_space_left(journal);
        if (space_left < nblocks) {
            int chkpt = journal->j_checkpoint_transactions != NULL;
            tid_t tid = 0;

            if (journal->j_committing_transaction)
                tid = journal->j_committing_transaction->t_tid;
            spin_unlock(&journal->j_list_lock);
            write_unlock(&journal->j_state_lock);
            if (chkpt) {
                jbd2_log_do_checkpoint(journal);
            } else if (jbd2_cleanup_journal_tail(journal) == 0) {
                /* We were able to recover space; yay! */
                ;
            } else if (tid) {
                jbd2_log_wait_commit(journal, tid);
            } else {
                printk(KERN_ERR "%s: needed %d blocks and "
                       "only had %d space available\n",
                       __func__, nblocks, space_left);
                printk(KERN_ERR "%s: no way to get more "
                       "journal space in %s\n", __func__,
                       journal->j_devname);
                WARN_ON(1);
                jbd2_journal_abort(journal, 0);
            }
            write_lock(&journal->j_state_lock);
        } else {
            spin_unlock(&journal->j_list_lock);
        }
        mutex_unlock(&journal->j_checkpoint_mutex);
    }
}

/*
 * Clean up transaction's list of buffers submitted for io.
 * We wait for any pending IO to complete and remove any clean
 * buffers. Note that we take the buffers in the opposite ordering
 * from the one in which they were submitted for IO.
 *
 * Return 0 on success, and return <0 if some buffers have failed
 * to be written out.
 *
 * Called with j_list_lock held.
 */
static int __wait_cp_io(journal_t *journal, transaction_t *transaction)
{
    struct journal_head *jh;
    struct buffer_head *bh;
    tid_t this_tid;
    int released = 0;
    int ret = 0;

    this_tid = transaction->t_tid;
restart:
    /* Did somebody clean up the transaction in the meanwhile? */
    if (journal->j_checkpoint_transactions != transaction ||
            transaction->t_tid != this_tid)
        return ret;
    while (!released && transaction->t_checkpoint_io_list) {
        jh = transaction->t_checkpoint_io_list;
        bh = jh2bh(jh);
        get_bh(bh);
        if (buffer_locked(bh)) {
            spin_unlock(&journal->j_list_lock);
            wait_on_buffer(bh);
            /* the journal_head may have gone by now */
            BUFFER_TRACE(bh, "brelse");
            __brelse(bh);
            spin_lock(&journal->j_list_lock);
            goto restart;
        }
        if (unlikely(buffer_write_io_error(bh)))
            ret = -EIO;

        /*
         * Now in whatever state the buffer currently is, we know that
         * it has been written out and so we can drop it from the list
         */
        released = __jbd2_journal_remove_checkpoint(jh);
        __brelse(bh);
    }

    return ret;
}

static void
__flush_batch(journal_t *journal, int *batch_count)
{
    int i;
    struct blk_plug plug;

    blk_start_plug(&plug);
    for (i = 0; i < *batch_count; i++)
        write_dirty_buffer(journal->j_chkpt_bhs[i], WRITE_SYNC);
    blk_finish_plug(&plug);

    for (i = 0; i < *batch_count; i++) {
        struct buffer_head *bh = journal->j_chkpt_bhs[i];
        BUFFER_TRACE(bh, "brelse");
        __brelse(bh);
    }
    *batch_count = 0;
}

/*
 * Try to flush one buffer from the checkpoint list to disk.
 *
 * Return 1 if something happened which requires us to abort the current
 * scan of the checkpoint list.  Return <0 if the buffer has failed to
 * be written out.
 *
 * Called with j_list_lock held and drops it if 1 is returned
 */
static int __process_buffer(journal_t *journal, struct journal_head *jh,
                int *batch_count, transaction_t *transaction)
{
    struct buffer_head *bh = jh2bh(jh);
    int ret = 0;

    if (buffer_locked(bh)) {
        get_bh(bh);
        spin_unlock(&journal->j_list_lock);
        wait_on_buffer(bh);
        /* the journal_head may have gone by now */
        BUFFER_TRACE(bh, "brelse");
        __brelse(bh);
        ret = 1;
    } else if (jh->b_transaction != NULL) {
        transaction_t *t = jh->b_transaction;
        tid_t tid = t->t_tid;

        transaction->t_chp_stats.cs_forced_to_close++;
        spin_unlock(&journal->j_list_lock);
        if (unlikely(journal->j_flags & JBD2_UNMOUNT))
            /*
             * The journal thread is dead; so starting and
             * waiting for a commit to finish will cause
             * us to wait for a _very_ long time.
             */
            printk(KERN_ERR "JBD2: %s: "
                   "Waiting for Godot: block %llu\n",
                   journal->j_devname,
                   (unsigned long long) bh->b_blocknr);
        jbd2_log_start_commit(journal, tid);
        jbd2_log_wait_commit(journal, tid);
        ret = 1;
    } else if (!buffer_dirty(bh)) {
        ret = 1;
        if (unlikely(buffer_write_io_error(bh)))
            ret = -EIO;
        get_bh(bh);
        BUFFER_TRACE(bh, "remove from checkpoint");
        __jbd2_journal_remove_checkpoint(jh);
        spin_unlock(&journal->j_list_lock);
        __brelse(bh);
    } else {
        /*
         * Important: we are about to write the buffer, and
         * possibly block, while still holding the journal lock.
         * We cannot afford to let the transaction logic start
         * messing around with this buffer before we write it to
         * disk, as that would break recoverability.
         */
        BUFFER_TRACE(bh, "queue");
        get_bh(bh);
        J_ASSERT_BH(bh, !buffer_jwrite(bh));
        journal->j_chkpt_bhs[*batch_count] = bh;
        __buffer_relink_io(jh);
        transaction->t_chp_stats.cs_written++;
        (*batch_count)++;
        if (*batch_count == JBD2_NR_BATCH) {
            spin_unlock(&journal->j_list_lock);
            __flush_batch(journal, batch_count);
            ret = 1;
        }
    }
    return ret;
}

/*
 * Perform an actual checkpoint. We take the first transaction on the
 * list of transactions to be checkpointed and send all its buffers
 * to disk. We submit larger chunks of data at once.
 *
 * The journal should be locked before calling this function.
 * Called with j_checkpoint_mutex held.
 */
int jbd2_log_do_checkpoint(journal_t *journal)
{
    transaction_t *transaction;
    tid_t this_tid;
    int result;

    jbd_debug(1, "Start checkpoint\n");

    /*
     * First thing: if there are any transactions in the log which
     * don't need checkpointing, just eliminate them from the
     * journal straight away.
     */
    result = jbd2_cleanup_journal_tail(journal);
    trace_jbd2_checkpoint(journal, result);
    jbd_debug(1, "cleanup_journal_tail returned %d\n", result);
    if (result <= 0)
        return result;

    /*
     * OK, we need to start writing disk blocks.  Take one transaction
     * and write it.
     */
    result = 0;
    spin_lock(&journal->j_list_lock);
    if (!journal->j_checkpoint_transactions)
        goto out;
    transaction = journal->j_checkpoint_transactions;
    if (transaction->t_chp_stats.cs_chp_time == 0)
        transaction->t_chp_stats.cs_chp_time = jiffies;
    this_tid = transaction->t_tid;
restart:
    /*
     * If someone cleaned up this transaction while we slept, we're
     * done (maybe it's a new transaction, but it fell at the same
     * address).
     */
    if (journal->j_checkpoint_transactions == transaction &&
            transaction->t_tid == this_tid) {
        int batch_count = 0;
        struct journal_head *jh;
        int retry = 0, err;

        while (!retry && transaction->t_checkpoint_list) {
            jh = transaction->t_checkpoint_list;
            retry = __process_buffer(journal, jh, &batch_count,
                         transaction);
            if (retry < 0 && !result)
                result = retry;
            if (!retry && (need_resched() ||
                spin_needbreak(&journal->j_list_lock))) {
                spin_unlock(&journal->j_list_lock);
                retry = 1;
                break;
            }
        }

        if (batch_count) {
            if (!retry) {
                spin_unlock(&journal->j_list_lock);
                retry = 1;
            }
            __flush_batch(journal, &batch_count);
        }

        if (retry) {
            spin_lock(&journal->j_list_lock);
            goto restart;
        }
        /*
         * Now we have cleaned up the first transaction's checkpoint
         * list. Let's clean up the second one
         */
        err = __wait_cp_io(journal, transaction);
        if (!result)
            result = err;
    }
out:
    spin_unlock(&journal->j_list_lock);
    if (result < 0)
        jbd2_journal_abort(journal, result);
    else
        result = jbd2_cleanup_journal_tail(journal);

    return (result < 0) ? result : 0;
}

/*
 * Check the list of checkpoint transactions for the journal to see if
 * we have already got rid of any since the last update of the log tail
 * in the journal superblock.  If so, we can instantly roll the
 * superblock forward to remove those transactions from the log.
 *
 * Return <0 on error, 0 on success, 1 if there was nothing to clean up.
 *
 * Called with the journal lock held.
 *
 * This is the only part of the journaling code which really needs to be
 * aware of transaction aborts.  Checkpointing involves writing to the
 * main filesystem area rather than to the journal, so it can proceed
 * even in abort state, but we must not update the super block if
 * checkpointing may have failed.  Otherwise, we would lose some metadata
 * buffers which should be written-back to the filesystem.
 */

int jbd2_cleanup_journal_tail(journal_t *journal)
{
    tid_t       first_tid;
    unsigned long   blocknr;

    if (is_journal_aborted(journal))
        return 1;

    if (!jbd2_journal_get_log_tail(journal, &first_tid, &blocknr))
        return 1;
    J_ASSERT(blocknr != 0);

    /*
     * We need to make sure that any blocks that were recently written out
     * --- perhaps by jbd2_log_do_checkpoint() --- are flushed out before
     * we drop the transactions from the journal. It's unlikely this will
     * be necessary, especially with an appropriately sized journal, but we
     * need this to guarantee correctness.  Fortunately
     * jbd2_cleanup_journal_tail() doesn't get called all that often.
     */
    if (journal->j_flags & JBD2_BARRIER)
        blkdev_issue_flush(journal->j_fs_dev, GFP_KERNEL, NULL);

    __jbd2_update_log_tail(journal, first_tid, blocknr);
    return 0;
}


/* Checkpoint list management */

/*
 * journal_clean_one_cp_list
 *
 * Find all the written-back checkpoint buffers in the given list and
 * release them.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 * Returns number of buffers reaped (for debug)
 */

static int journal_clean_one_cp_list(struct journal_head *jh, int *released)
{
    struct journal_head *last_jh;
    struct journal_head *next_jh = jh;
    int ret, freed = 0;

    *released = 0;
    if (!jh)
        return 0;

    last_jh = jh->b_cpprev;
    do {
        jh = next_jh;
        next_jh = jh->b_cpnext;
        ret = __try_to_free_cp_buf(jh);
        if (ret) {
            freed++;
            if (ret == 2) {
                *released = 1;
                return freed;
            }
        }
        /*
         * This function only frees up some memory
         * if possible so we dont have an obligation
         * to finish processing. Bail out if preemption
         * requested:
         */
        if (need_resched())
            return freed;
    } while (jh != last_jh);

    return freed;
}

/*
 * journal_clean_checkpoint_list
 *
 * Find all the written-back checkpoint buffers in the journal and release them.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 * Returns number of buffers reaped (for debug)
 */

int __jbd2_journal_clean_checkpoint_list(journal_t *journal)
{
    transaction_t *transaction, *last_transaction, *next_transaction;
    int ret = 0;
    int released;

    transaction = journal->j_checkpoint_transactions;
    if (!transaction)
        goto out;

    last_transaction = transaction->t_cpprev;
    next_transaction = transaction;
    do {
        transaction = next_transaction;
        next_transaction = transaction->t_cpnext;
        ret += journal_clean_one_cp_list(transaction->
                t_checkpoint_list, &released);
        /*
         * This function only frees up some memory if possible so we
         * dont have an obligation to finish processing. Bail out if
         * preemption requested:
         */
        if (need_resched())
            goto out;
        if (released)
            continue;
        /*
         * It is essential that we are as careful as in the case of
         * t_checkpoint_list with removing the buffer from the list as
         * we can possibly see not yet submitted buffers on io_list
         */
        ret += journal_clean_one_cp_list(transaction->
                t_checkpoint_io_list, &released);
        if (need_resched())
            goto out;
    } while (transaction != last_transaction);
out:
    return ret;
}

/*
 * journal_remove_checkpoint: called after a buffer has been committed
 * to disk (either by being write-back flushed to disk, or being
 * committed to the log).
 *
 * We cannot safely clean a transaction out of the log until all of the
 * buffer updates committed in that transaction have safely been stored
 * elsewhere on disk.  To achieve this, all of the buffers in a
 * transaction need to be maintained on the transaction's checkpoint
 * lists until they have been rewritten, at which point this function is
 * called to remove the buffer from the existing transaction's
 * checkpoint lists.
 *
 * The function returns 1 if it frees the transaction, 0 otherwise.
 * The function can free jh and bh.
 *
 * This function is called with j_list_lock held.
 */
int __jbd2_journal_remove_checkpoint(struct journal_head *jh)
{
    struct transaction_chp_stats_s *stats;
    transaction_t *transaction;
    journal_t *journal;
    int ret = 0;

    JBUFFER_TRACE(jh, "entry");

    if ((transaction = jh->b_cp_transaction) == NULL) {
        JBUFFER_TRACE(jh, "not on transaction");
        goto out;
    }
    journal = transaction->t_journal;

    JBUFFER_TRACE(jh, "removing from transaction");
    __buffer_unlink(jh);
    jh->b_cp_transaction = NULL;
    jbd2_journal_put_journal_head(jh);

    if (transaction->t_checkpoint_list != NULL ||
        transaction->t_checkpoint_io_list != NULL)
        goto out;

    /*
     * There is one special case to worry about: if we have just pulled the
     * buffer off a running or committing transaction's checkpoing list,
     * then even if the checkpoint list is empty, the transaction obviously
     * cannot be dropped!
     *
     * The locking here around t_state is a bit sleazy.
     * See the comment at the end of jbd2_journal_commit_transaction().
     */
    if (transaction->t_state != T_FINISHED)
        goto out;

    /* OK, that was the last buffer for the transaction: we can now
       safely remove this transaction from the log */
    stats = &transaction->t_chp_stats;
    if (stats->cs_chp_time)
        stats->cs_chp_time = jbd2_time_diff(stats->cs_chp_time,
                            jiffies);
    trace_jbd2_checkpoint_stats(journal->j_fs_dev->bd_dev,
                    transaction->t_tid, stats);

    __jbd2_journal_drop_transaction(journal, transaction);
    jbd2_journal_free_transaction(transaction);

    /* Just in case anybody was waiting for more transactions to be
           checkpointed... */
    wake_up(&journal->j_wait_logspace);
    ret = 1;
out:
    return ret;
}

/*
 * journal_insert_checkpoint: put a committed buffer onto a checkpoint
 * list so that we know when it is safe to clean the transaction out of
 * the log.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 */
void __jbd2_journal_insert_checkpoint(struct journal_head *jh,
                   transaction_t *transaction)
{
    JBUFFER_TRACE(jh, "entry");
    J_ASSERT_JH(jh, buffer_dirty(jh2bh(jh)) || buffer_jbddirty(jh2bh(jh)));
    J_ASSERT_JH(jh, jh->b_cp_transaction == NULL);

    /* Get reference for checkpointing transaction */
    jbd2_journal_grab_journal_head(jh2bh(jh));
    jh->b_cp_transaction = transaction;

    if (!transaction->t_checkpoint_list) {
        jh->b_cpnext = jh->b_cpprev = jh;
    } else {
        jh->b_cpnext = transaction->t_checkpoint_list;
        jh->b_cpprev = transaction->t_checkpoint_list->b_cpprev;
        jh->b_cpprev->b_cpnext = jh;
        jh->b_cpnext->b_cpprev = jh;
    }
    transaction->t_checkpoint_list = jh;
}

/*
 * We've finished with this transaction structure: adios...
 *
 * The transaction must have no links except for the checkpoint by this
 * point.
 *
 * Called with the journal locked.
 * Called with j_list_lock held.
 */

void __jbd2_journal_drop_transaction(journal_t *journal, transaction_t *transaction)
{
    assert_spin_locked(&journal->j_list_lock);
    if (transaction->t_cpnext) {
        transaction->t_cpnext->t_cpprev = transaction->t_cpprev;
        transaction->t_cpprev->t_cpnext = transaction->t_cpnext;
        if (journal->j_checkpoint_transactions == transaction)
            journal->j_checkpoint_transactions =
                transaction->t_cpnext;
        if (journal->j_checkpoint_transactions == transaction)
            journal->j_checkpoint_transactions = NULL;
    }

    J_ASSERT(transaction->t_state == T_FINISHED);
    J_ASSERT(transaction->t_buffers == NULL);
    J_ASSERT(transaction->t_forget == NULL);
    J_ASSERT(transaction->t_iobuf_list == NULL);
    J_ASSERT(transaction->t_shadow_list == NULL);
    J_ASSERT(transaction->t_log_list == NULL);
    J_ASSERT(transaction->t_checkpoint_list == NULL);
    J_ASSERT(transaction->t_checkpoint_io_list == NULL);
    J_ASSERT(atomic_read(&transaction->t_updates) == 0);
    J_ASSERT(journal->j_committing_transaction != transaction);
    J_ASSERT(journal->j_running_transaction != transaction);

    trace_jbd2_drop_transaction(journal, transaction);

    jbd_debug(1, "Dropping transaction %d, all done\n", transaction->t_tid);
}