/*
   * linux/fs/jbd/checkpoint.c
   *
   * Written by Stephen C. Tweedie <sct@redhat.com>, 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/jbd.h>
  #include <linux/errno.h>
  #include <linux/slab.h>
  #include <linux/blkdev.h>
  #include <trace/events/jbd.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
   * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
   */
  static int __try_to_free_cp_buf(struct journal_head *jh)
  {
  	int ret = 0;
  	struct buffer_head *bh = jh2bh(jh);
  
  	if (jh->b_jlist == BJ_None && !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 = __journal_remove_checkpoint(jh) + 1;
  		jbd_unlock_bh_state(bh);
  		BUFFER_TRACE(bh, "release");
  		__brelse(bh);
  	} else {
  		jbd_unlock_bh_state(bh);
  	}
  	return ret;
  }
  
  /*
   * __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 __log_wait_for_space(journal_t *journal)
  {
  	int nblocks, space_left;
  	assert_spin_locked(&journal->j_state_lock);
  
  	nblocks = jbd_space_needed(journal);
  	while (__log_space_left(journal) < nblocks) {
  		if (journal->j_flags & JFS_ABORT)
  			return;
  		spin_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.
  		 */
  		spin_lock(&journal->j_state_lock);
  		spin_lock(&journal->j_list_lock);
  		nblocks = jbd_space_needed(journal);
  		space_left = __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);
  			spin_unlock(&journal->j_state_lock);
  			if (chkpt) {
  				log_do_checkpoint(journal);
  			} else if (cleanup_journal_tail(journal) == 0) {
  				/* We were able to recover space; yay! */
  				;
  			} else if (tid) {
  				log_wait_commit(journal, tid);
  			} else {
  				printk(KERN_ERR "%s: needed %d blocks and "
  				       "only had %d space available
  ",
  				       __func__, nblocks, space_left);
  				printk(KERN_ERR "%s: no way to get more "
  				       "journal space
  ", __func__);
  				WARN_ON(1);
  				journal_abort(journal, 0);
  			}
  			spin_lock(&journal->j_state_lock);
  		} else {
  			spin_unlock(&journal->j_list_lock);
  		}
  		mutex_unlock(&journal->j_checkpoint_mutex);
  	}
  }
  
  /*
   * We were unable to perform jbd_trylock_bh_state() inside j_list_lock.
   * The caller must restart a list walk.  Wait for someone else to run
   * jbd_unlock_bh_state().
   */
  static void jbd_sync_bh(journal_t *journal, struct buffer_head *bh)
  	__releases(journal->j_list_lock)
  {
  	get_bh(bh);
  	spin_unlock(&journal->j_list_lock);
  	jbd_lock_bh_state(bh);
  	jbd_unlock_bh_state(bh);
  	put_bh(bh);
  }
  
  /*
   * 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);
  		if (!jbd_trylock_bh_state(bh)) {
  			jbd_sync_bh(journal, bh);
  			spin_lock(&journal->j_list_lock);
  			goto restart;
  		}
  		get_bh(bh);
  		if (buffer_locked(bh)) {
  			spin_unlock(&journal->j_list_lock);
  			jbd_unlock_bh_state(bh);
  			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 = __journal_remove_checkpoint(jh);
  		jbd_unlock_bh_state(bh);
  		__brelse(bh);
  	}
  
  	return ret;
  }
  
  #define NR_BATCH	64
  
  static void
  __flush_batch(journal_t *journal, struct buffer_head **bhs, int *batch_count)
  {
  	int i;
  	struct blk_plug plug;
  
  	blk_start_plug(&plug);
  	for (i = 0; i < *batch_count; i++)
  		write_dirty_buffer(bhs[i], WRITE_SYNC);
  	blk_finish_plug(&plug);
  
  	for (i = 0; i < *batch_count; i++) {
  		struct buffer_head *bh = bhs[i];
  		clear_buffer_jwrite(bh);
  		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
   * Called under jbd_lock_bh_state(jh2bh(jh)), and drops it
   */
  static int __process_buffer(journal_t *journal, struct journal_head *jh,
  			struct buffer_head **bhs, int *batch_count)
  {
  	struct buffer_head *bh = jh2bh(jh);
  	int ret = 0;
  
  	if (buffer_locked(bh)) {
  		get_bh(bh);
  		spin_unlock(&journal->j_list_lock);
  		jbd_unlock_bh_state(bh);
  		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;
  
  		spin_unlock(&journal->j_list_lock);
  		jbd_unlock_bh_state(bh);
  		log_start_commit(journal, tid);
  		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);
  		J_ASSERT_JH(jh, !buffer_jbddirty(bh));
  		BUFFER_TRACE(bh, "remove from checkpoint");
  		__journal_remove_checkpoint(jh);
  		spin_unlock(&journal->j_list_lock);
  		jbd_unlock_bh_state(bh);
  		__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));
  		set_buffer_jwrite(bh);
  		bhs[*batch_count] = bh;
  		__buffer_relink_io(jh);
  		jbd_unlock_bh_state(bh);
  		(*batch_count)++;
  		if (*batch_count == NR_BATCH) {
  			spin_unlock(&journal->j_list_lock);
  			__flush_batch(journal, bhs, 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 log_do_checkpoint(journal_t *journal)
  {
  	transaction_t *transaction;
  	tid_t this_tid;
  	int result;
  
  	jbd_debug(1, "Start checkpoint
  ");
  
  	/*
  	 * First thing: if there are any transactions in the log which
  	 * don't need checkpointing, just eliminate them from the
  	 * journal straight away.
  	 */
  	result = cleanup_journal_tail(journal);
  	trace_jbd_checkpoint(journal, result);
  	jbd_debug(1, "cleanup_journal_tail returned %d
  ", 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;
  	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 buffer_head *bhs[NR_BATCH];
  		struct journal_head *jh;
  		int retry = 0, err;
  
  		while (!retry && transaction->t_checkpoint_list) {
  			struct buffer_head *bh;
  
  			jh = transaction->t_checkpoint_list;
  			bh = jh2bh(jh);
  			if (!jbd_trylock_bh_state(bh)) {
  				jbd_sync_bh(journal, bh);
  				retry = 1;
  				break;
  			}
  			retry = __process_buffer(journal, jh, bhs,&batch_count);
  			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, bhs, &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)
  		journal_abort(journal, result);
  	else
  		result = 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.
   *
   * 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 cleanup_journal_tail(journal_t *journal)
  {
  	transaction_t * transaction;
  	tid_t		first_tid;
  	unsigned int	blocknr, freed;
  
  	if (is_journal_aborted(journal))
  		return 1;
  
  	/*
  	 * OK, work out the oldest transaction remaining in the log, and
  	 * the log block it starts at.
  	 *
  	 * If the log is now empty, we need to work out which is the
  	 * next transaction ID we will write, and where it will
  	 * start.
  	 */
  	spin_lock(&journal->j_state_lock);
  	spin_lock(&journal->j_list_lock);
  	transaction = journal->j_checkpoint_transactions;
  	if (transaction) {
  		first_tid = transaction->t_tid;
  		blocknr = transaction->t_log_start;
  	} else if ((transaction = journal->j_committing_transaction) != NULL) {
  		first_tid = transaction->t_tid;
  		blocknr = transaction->t_log_start;
  	} else if ((transaction = journal->j_running_transaction) != NULL) {
  		first_tid = transaction->t_tid;
  		blocknr = journal->j_head;
  	} else {
  		first_tid = journal->j_transaction_sequence;
  		blocknr = journal->j_head;
  	}
  	spin_unlock(&journal->j_list_lock);
  	J_ASSERT(blocknr != 0);
  
  	/* If the oldest pinned transaction is at the tail of the log
             already then there's not much we can do right now. */
  	if (journal->j_tail_sequence == first_tid) {
  		spin_unlock(&journal->j_state_lock);
  		return 1;
  	}
  	spin_unlock(&journal->j_state_lock);
  
  	/*
  	 * We need to make sure that any blocks that were recently written out
  	 * --- perhaps by log_do_checkpoint() --- are flushed out before we
  	 * drop the transactions from the journal. Similarly we need to be sure
  	 * superblock makes it to disk before next transaction starts reusing
  	 * freed space (otherwise we could replay some blocks of the new
  	 * transaction thinking they belong to the old one). So we use
  	 * WRITE_FLUSH_FUA. It's unlikely this will be necessary, especially
  	 * with an appropriately sized journal, but we need this to guarantee
  	 * correctness.  Fortunately cleanup_journal_tail() doesn't get called
  	 * all that often.
  	 */
  	journal_update_sb_log_tail(journal, first_tid, blocknr,
  				   WRITE_FLUSH_FUA);
  
  	spin_lock(&journal->j_state_lock);
  	/* OK, update the superblock to recover the freed space.
  	 * Physical blocks come first: have we wrapped beyond the end of
  	 * the log?  */
  	freed = blocknr - journal->j_tail;
  	if (blocknr < journal->j_tail)
  		freed = freed + journal->j_last - journal->j_first;
  
  	trace_jbd_cleanup_journal_tail(journal, first_tid, blocknr, freed);
  	jbd_debug(1,
  		  "Cleaning journal tail from %d to %d (offset %u), "
  		  "freeing %u
  ",
  		  journal->j_tail_sequence, first_tid, blocknr, freed);
  
  	journal->j_free += freed;
  	journal->j_tail_sequence = first_tid;
  	journal->j_tail = blocknr;
  	spin_unlock(&journal->j_state_lock);
  	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 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;
  		/* Use trylock because of the ranking */
  		if (jbd_trylock_bh_state(jh2bh(jh))) {
  			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 __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.
   * This function is called with jbd_lock_bh_state(jh2bh(jh))
   */
  
  int __journal_remove_checkpoint(struct journal_head *jh)
  {
  	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;
  	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 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 */
  
  	__journal_drop_transaction(journal, 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 __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 */
  	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 __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_sync_datalist == 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(transaction->t_updates == 0);
  	J_ASSERT(journal->j_committing_transaction != transaction);
  	J_ASSERT(journal->j_running_transaction != transaction);
  
  	trace_jbd_drop_transaction(journal, transaction);
  	jbd_debug(1, "Dropping transaction %d, all done
  ", transaction->t_tid);
  	kfree(transaction);
  }