// SPDX-License-Identifier: GPL-2.0+
/*
 * linux/fs/jbd2/checkpoint.c
 *
 * Written by Stephen C. Tweedie <sct@redhat.com>, 1999
 *
 * Copyright 1999 Red Hat Software --- All Rights Reserved
 *
 * 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;
}

/*
 * Check a checkpoint buffer could be release or not.
 *
 * Requires j_list_lock
 */
static inline bool __cp_buffer_busy(struct journal_head *jh)
{
        struct buffer_head *bh = jh2bh(jh);

        return (jh->b_transaction || buffer_locked(bh) || buffer_dirty(bh));
}

/*
 * __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)
__acquires(&journal->j_state_lock)
__releases(&journal->j_state_lock)
{
        int nblocks, space_left;
        /* assert_spin_locked(&journal->j_state_lock); */

        nblocks = journal->j_max_transaction_buffers;
        while (jbd2_log_space_left(journal) < nblocks) {
                write_unlock(&journal->j_state_lock);
                mutex_lock_io(&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);
                if (journal->j_flags & JBD2_ABORT) {
                        mutex_unlock(&journal->j_checkpoint_mutex);
                        return;
                }
                spin_lock(&journal->j_list_lock);
                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_journal_commit_transaction() may want
                                 * to take the checkpoint_mutex if JBD2_FLUSHED
                                 * is set.  So we need to temporarily drop it.
                                 */
                                mutex_unlock(&journal->j_checkpoint_mutex);
                                jbd2_log_wait_commit(journal, tid);
                                write_lock(&journal->j_state_lock);
                                continue;
                        } 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, -EIO);
                        }
                        write_lock(&journal->j_state_lock);
                } else {
                        spin_unlock(&journal->j_list_lock);
                }
                mutex_unlock(&journal->j_checkpoint_mutex);
        }
}

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], REQ_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;
}

/*
 * 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)
{
        struct journal_head     *jh;
        struct buffer_head      *bh;
        transaction_t           *transaction;
        tid_t                   this_tid;
        int                     result, batch_count = 0;

        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.
         */
        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)
                goto out;

        /* checkpoint all of the transaction's buffers */
        while (transaction->t_checkpoint_list) {
                jh = transaction->t_checkpoint_list;
                bh = jh2bh(jh);

                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);
                        goto retry;
                }
                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);

                        if (batch_count)
                                __flush_batch(journal, &batch_count);
                        jbd2_log_start_commit(journal, tid);
                        /*
                         * jbd2_journal_commit_transaction() may want
                         * to take the checkpoint_mutex if JBD2_FLUSHED
                         * is set, jbd2_update_log_tail() called by
                         * jbd2_journal_commit_transaction() may also take
                         * checkpoint_mutex.  So we need to temporarily
                         * drop it.
                         */
                        mutex_unlock(&journal->j_checkpoint_mutex);
                        jbd2_log_wait_commit(journal, tid);
                        mutex_lock_io(&journal->j_checkpoint_mutex);
                        spin_lock(&journal->j_list_lock);
                        goto restart;
                }
                if (!buffer_dirty(bh)) {
                        BUFFER_TRACE(bh, "remove from checkpoint");
                        if (__jbd2_journal_remove_checkpoint(jh))
                                /* The transaction was released; we're done */
                                goto out;
                        continue;
                }
                /*
                 * 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++;
                if ((batch_count == JBD2_NR_BATCH) ||
                    need_resched() ||
                    spin_needbreak(&journal->j_list_lock))
                        goto unlock_and_flush;
        }

        if (batch_count) {
                unlock_and_flush:
                        spin_unlock(&journal->j_list_lock);
                retry:
                        if (batch_count)
                                __flush_batch(journal, &batch_count);
                        spin_lock(&journal->j_list_lock);
                        goto restart;
        }

        /*
         * Now we issued all of the transaction's buffers, let's deal
         * with the buffers that are out for I/O.
         */
restart2:
        /* Did somebody clean up the transaction in the meanwhile? */
        if (journal->j_checkpoint_transactions != transaction ||
            transaction->t_tid != this_tid)
                goto out;

        while (transaction->t_checkpoint_io_list) {
                jh = transaction->t_checkpoint_io_list;
                bh = jh2bh(jh);
                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);
                        spin_lock(&journal->j_list_lock);
                        goto restart2;
                }

                /*
                 * 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
                 */
                if (__jbd2_journal_remove_checkpoint(jh))
                        break;
        }
out:
        spin_unlock(&journal->j_list_lock);
        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 -EIO;

        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);

        return __jbd2_update_log_tail(journal, first_tid, blocknr);
}


/* Checkpoint list management */

/*
 * journal_clean_one_cp_list
 *
 * Find all the written-back checkpoint buffers in the given list and
 * release them. If 'destroy' is set, clean all buffers unconditionally.
 *
 * Called with j_list_lock held.
 * Returns 1 if we freed the transaction, 0 otherwise.
 */
static int journal_clean_one_cp_list(struct journal_head *jh, bool destroy)
{
        struct journal_head *last_jh;
        struct journal_head *next_jh = jh;

        if (!jh)
                return 0;

        last_jh = jh->b_cpprev;
        do {
                jh = next_jh;
                next_jh = jh->b_cpnext;

                if (!destroy && __cp_buffer_busy(jh))
                        return 0;

                if (__jbd2_journal_remove_checkpoint(jh))
                        return 1;
                /*
                 * 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 0;
        } while (jh != last_jh);

        return 0;
}

/*
 * journal_shrink_one_cp_list
 *
 * Find 'nr_to_scan' written-back checkpoint buffers in the given list
 * and try to release them. If the whole transaction is released, set
 * the 'released' parameter. Return the number of released checkpointed
 * buffers.
 *
 * Called with j_list_lock held.
 */
static unsigned long journal_shrink_one_cp_list(struct journal_head *jh,
                                                unsigned long *nr_to_scan,
                                                bool *released)
{
        struct journal_head *last_jh;
        struct journal_head *next_jh = jh;
        unsigned long nr_freed = 0;
        int ret;

        if (!jh || *nr_to_scan == 0)
                return 0;

        last_jh = jh->b_cpprev;
        do {
                jh = next_jh;
                next_jh = jh->b_cpnext;

                (*nr_to_scan)--;
                if (__cp_buffer_busy(jh))
                        continue;

                nr_freed++;
                ret = __jbd2_journal_remove_checkpoint(jh);
                if (ret) {
                        *released = true;
                        break;
                }

                if (need_resched())
                        break;
        } while (jh != last_jh && *nr_to_scan);

        return nr_freed;
}

/*
 * jbd2_journal_shrink_checkpoint_list
 *
 * Find 'nr_to_scan' written-back checkpoint buffers in the journal
 * and try to release them. Return the number of released checkpointed
 * buffers.
 *
 * Called with j_list_lock held.
 */
unsigned long jbd2_journal_shrink_checkpoint_list(journal_t *journal,
                                                  unsigned long *nr_to_scan)
{
        transaction_t *transaction, *last_transaction, *next_transaction;
        bool released;
        tid_t first_tid = 0, last_tid = 0, next_tid = 0;
        tid_t tid = 0;
        unsigned long nr_freed = 0;
        unsigned long nr_scanned = *nr_to_scan;

again:
        spin_lock(&journal->j_list_lock);
        if (!journal->j_checkpoint_transactions) {
                spin_unlock(&journal->j_list_lock);
                goto out;
        }

        /*
         * Get next shrink transaction, resume previous scan or start
         * over again. If some others do checkpoint and drop transaction
         * from the checkpoint list, we ignore saved j_shrink_transaction
         * and start over unconditionally.
         */
        if (journal->j_shrink_transaction)
                transaction = journal->j_shrink_transaction;
        else
                transaction = journal->j_checkpoint_transactions;

        if (!first_tid)
                first_tid = transaction->t_tid;
        last_transaction = journal->j_checkpoint_transactions->t_cpprev;
        next_transaction = transaction;
        last_tid = last_transaction->t_tid;
        do {
                transaction = next_transaction;
                next_transaction = transaction->t_cpnext;
                tid = transaction->t_tid;
                released = false;

                nr_freed += journal_shrink_one_cp_list(transaction->t_checkpoint_list,
                                                       nr_to_scan, &released);
                if (*nr_to_scan == 0)
                        break;
                if (need_resched() || spin_needbreak(&journal->j_list_lock))
                        break;
                if (released)
                        continue;

                nr_freed += journal_shrink_one_cp_list(transaction->t_checkpoint_io_list,
                                                       nr_to_scan, &released);
                if (*nr_to_scan == 0)
                        break;
                if (need_resched() || spin_needbreak(&journal->j_list_lock))
                        break;
        } while (transaction != last_transaction);

        if (transaction != last_transaction) {
                journal->j_shrink_transaction = next_transaction;
                next_tid = next_transaction->t_tid;
        } else {
                journal->j_shrink_transaction = NULL;
                next_tid = 0;
        }

        spin_unlock(&journal->j_list_lock);
        cond_resched();

        if (*nr_to_scan && next_tid)
                goto again;
out:
        nr_scanned -= *nr_to_scan;
        trace_jbd2_shrink_checkpoint_list(journal, first_tid, tid, last_tid,
                                          nr_freed, nr_scanned, next_tid);

        return nr_freed;
}

/*
 * journal_clean_checkpoint_list
 *
 * Find all the written-back checkpoint buffers in the journal and release them.
 * If 'destroy' is set, release all buffers unconditionally.
 *
 * Called with j_list_lock held.
 */
void __jbd2_journal_clean_checkpoint_list(journal_t *journal, bool destroy)
{
        transaction_t *transaction, *last_transaction, *next_transaction;
        int ret;

        transaction = journal->j_checkpoint_transactions;
        if (!transaction)
                return;

        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,
                                                destroy);
                /*
                 * 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;
                if (ret)
                        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, destroy);
                if (need_resched())
                        return;
                /*
                 * Stop scanning if we couldn't free the transaction. This
                 * avoids pointless scanning of transactions which still
                 * weren't checkpointed.
                 */
                if (!ret)
                        return;
        } while (transaction != last_transaction);
}

/*
 * Remove buffers from all checkpoint lists as journal is aborted and we just
 * need to free memory
 */
void jbd2_journal_destroy_checkpoint(journal_t *journal)
{
        /*
         * We loop because __jbd2_journal_clean_checkpoint_list() may abort
         * early due to a need of rescheduling.
         */
        while (1) {
                spin_lock(&journal->j_list_lock);
                if (!journal->j_checkpoint_transactions) {
                        spin_unlock(&journal->j_list_lock);
                        break;
                }
                __jbd2_journal_clean_checkpoint_list(journal, true);
                spin_unlock(&journal->j_list_lock);
                cond_resched();
        }
}

/*
 * 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;
        struct buffer_head *bh = jh2bh(jh);

        JBUFFER_TRACE(jh, "entry");

        transaction = jh->b_cp_transaction;
        if (!transaction) {
                JBUFFER_TRACE(jh, "not on transaction");
                return 0;
        }
        journal = transaction->t_journal;

        JBUFFER_TRACE(jh, "removing from transaction");

        /*
         * If we have failed to write the buffer out to disk, the filesystem
         * may become inconsistent. We cannot abort the journal here since
         * we hold j_list_lock and we have to be careful about races with
         * jbd2_journal_destroy(). So mark the writeback IO error in the
         * journal here and we abort the journal later from a better context.
         */
        if (buffer_write_io_error(bh))
                set_bit(JBD2_CHECKPOINT_IO_ERROR, &journal->j_atomic_flags);

        __buffer_unlink(jh);
        jh->b_cp_transaction = NULL;
        percpu_counter_dec(&journal->j_checkpoint_jh_count);
        jbd2_journal_put_journal_head(jh);

        /* Is this transaction empty? */
        if (transaction->t_checkpoint_list || transaction->t_checkpoint_io_list)
                return 0;

        /*
         * 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)
                return 0;

        /*
         * 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);
        return 1;
}

/*
 * 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;
        percpu_counter_inc(&transaction->t_journal->j_checkpoint_jh_count);
}

/*
 * 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);

        journal->j_shrink_transaction = NULL;
        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_shadow_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);
}