Initial import

1 files changed, 1021 insertions, 0 deletions

diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
new file mode 100644
index 000000000..bb217dcb4
--- /dev/null
+++ b/fs/jbd/commit.c
@@ -0,0 +1,1021 @@
+/*
+ * linux/fs/jbd/commit.c
+ *
+ * Written by Stephen C. Tweedie <sct@redhat.com>, 1998
+ *
+ * Copyright 1998 Red Hat corp --- 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.
+ *
+ * Journal commit routines for the generic filesystem journaling code;
+ * part of the ext2fs journaling system.
+ */
+
+#include <linux/time.h>
+#include <linux/fs.h>
+#include <linux/jbd.h>
+#include <linux/errno.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <trace/events/jbd.h>
+
+/*
+ * Default IO end handler for temporary BJ_IO buffer_heads.
+ */
+static void journal_end_buffer_io_sync(struct buffer_head *bh, int uptodate)
+{
+	BUFFER_TRACE(bh, "");
+	if (uptodate)
+		set_buffer_uptodate(bh);
+	else
+		clear_buffer_uptodate(bh);
+	unlock_buffer(bh);
+}
+
+/*
+ * When an ext3-ordered file is truncated, it is possible that many pages are
+ * not successfully freed, because they are attached to a committing transaction.
+ * After the transaction commits, these pages are left on the LRU, with no
+ * ->mapping, and with attached buffers.  These pages are trivially reclaimable
+ * by the VM, but their apparent absence upsets the VM accounting, and it makes
+ * the numbers in /proc/meminfo look odd.
+ *
+ * So here, we have a buffer which has just come off the forget list.  Look to
+ * see if we can strip all buffers from the backing page.
+ *
+ * Called under journal->j_list_lock.  The caller provided us with a ref
+ * against the buffer, and we drop that here.
+ */
+static void release_buffer_page(struct buffer_head *bh)
+{
+	struct page *page;
+
+	if (buffer_dirty(bh))
+		goto nope;
+	if (atomic_read(&bh->b_count) != 1)
+		goto nope;
+	page = bh->b_page;
+	if (!page)
+		goto nope;
+	if (page->mapping)
+		goto nope;
+
+	/* OK, it's a truncated page */
+	if (!trylock_page(page))
+		goto nope;
+
+	page_cache_get(page);
+	__brelse(bh);
+	try_to_free_buffers(page);
+	unlock_page(page);
+	page_cache_release(page);
+	return;
+
+nope:
+	__brelse(bh);
+}
+
+/*
+ * Decrement reference counter for data buffer. If it has been marked
+ * 'BH_Freed', release it and the page to which it belongs if possible.
+ */
+static void release_data_buffer(struct buffer_head *bh)
+{
+	if (buffer_freed(bh)) {
+		WARN_ON_ONCE(buffer_dirty(bh));
+		clear_buffer_freed(bh);
+		clear_buffer_mapped(bh);
+		clear_buffer_new(bh);
+		clear_buffer_req(bh);
+		bh->b_bdev = NULL;
+		release_buffer_page(bh);
+	} else
+		put_bh(bh);
+}
+
+/*
+ * Try to acquire jbd_lock_bh_state() against the buffer, when j_list_lock is
+ * held.  For ranking reasons we must trylock.  If we lose, schedule away and
+ * return 0.  j_list_lock is dropped in this case.
+ */
+static int inverted_lock(journal_t *journal, struct buffer_head *bh)
+{
+	if (!jbd_trylock_bh_state(bh)) {
+		spin_unlock(&journal->j_list_lock);
+		schedule();
+		return 0;
+	}
+	return 1;
+}
+
+/* Done it all: now write the commit record.  We should have
+ * cleaned up our previous buffers by now, so if we are in abort
+ * mode we can now just skip the rest of the journal write
+ * entirely.
+ *
+ * Returns 1 if the journal needs to be aborted or 0 on success
+ */
+static int journal_write_commit_record(journal_t *journal,
+					transaction_t *commit_transaction)
+{
+	struct journal_head *descriptor;
+	struct buffer_head *bh;
+	journal_header_t *header;
+	int ret;
+
+	if (is_journal_aborted(journal))
+		return 0;
+
+	descriptor = journal_get_descriptor_buffer(journal);
+	if (!descriptor)
+		return 1;
+
+	bh = jh2bh(descriptor);
+
+	header = (journal_header_t *)(bh->b_data);
+	header->h_magic = cpu_to_be32(JFS_MAGIC_NUMBER);
+	header->h_blocktype = cpu_to_be32(JFS_COMMIT_BLOCK);
+	header->h_sequence = cpu_to_be32(commit_transaction->t_tid);
+
+	JBUFFER_TRACE(descriptor, "write commit block");
+	set_buffer_dirty(bh);
+
+	if (journal->j_flags & JFS_BARRIER)
+		ret = __sync_dirty_buffer(bh, WRITE_SYNC | WRITE_FLUSH_FUA);
+	else
+		ret = sync_dirty_buffer(bh);
+
+	put_bh(bh);		/* One for getblk() */
+	journal_put_journal_head(descriptor);
+
+	return (ret == -EIO);
+}
+
+static void journal_do_submit_data(struct buffer_head **wbuf, int bufs,
+				   int write_op)
+{
+	int i;
+
+	for (i = 0; i < bufs; i++) {
+		wbuf[i]->b_end_io = end_buffer_write_sync;
+		/*
+		 * Here we write back pagecache data that may be mmaped. Since
+		 * we cannot afford to clean the page and set PageWriteback
+		 * here due to lock ordering (page lock ranks above transaction
+		 * start), the data can change while IO is in flight. Tell the
+		 * block layer it should bounce the bio pages if stable data
+		 * during write is required.
+		 *
+		 * We use up our safety reference in submit_bh().
+		 */
+		_submit_bh(write_op, wbuf[i], 1 << BIO_SNAP_STABLE);
+	}
+}
+
+/*
+ *  Submit all the data buffers to disk
+ */
+static int journal_submit_data_buffers(journal_t *journal,
+				       transaction_t *commit_transaction,
+				       int write_op)
+{
+	struct journal_head *jh;
+	struct buffer_head *bh;
+	int locked;
+	int bufs = 0;
+	struct buffer_head **wbuf = journal->j_wbuf;
+	int err = 0;
+
+	/*
+	 * Whenever we unlock the journal and sleep, things can get added
+	 * onto ->t_sync_datalist, so we have to keep looping back to
+	 * write_out_data until we *know* that the list is empty.
+	 *
+	 * Cleanup any flushed data buffers from the data list.  Even in
+	 * abort mode, we want to flush this out as soon as possible.
+	 */
+write_out_data:
+	cond_resched();
+	spin_lock(&journal->j_list_lock);
+
+	while (commit_transaction->t_sync_datalist) {
+		jh = commit_transaction->t_sync_datalist;
+		bh = jh2bh(jh);
+		locked = 0;
+
+		/* Get reference just to make sure buffer does not disappear
+		 * when we are forced to drop various locks */
+		get_bh(bh);
+		/* If the buffer is dirty, we need to submit IO and hence
+		 * we need the buffer lock. We try to lock the buffer without
+		 * blocking. If we fail, we need to drop j_list_lock and do
+		 * blocking lock_buffer().
+		 */
+		if (buffer_dirty(bh)) {
+			if (!trylock_buffer(bh)) {
+				BUFFER_TRACE(bh, "needs blocking lock");
+				spin_unlock(&journal->j_list_lock);
+				trace_jbd_do_submit_data(journal,
+						     commit_transaction);
+				/* Write out all data to prevent deadlocks */
+				journal_do_submit_data(wbuf, bufs, write_op);
+				bufs = 0;
+				lock_buffer(bh);
+				spin_lock(&journal->j_list_lock);
+			}
+			locked = 1;
+		}
+		/* We have to get bh_state lock. Again out of order, sigh. */
+		if (!inverted_lock(journal, bh)) {
+			jbd_lock_bh_state(bh);
+			spin_lock(&journal->j_list_lock);
+		}
+		/* Someone already cleaned up the buffer? */
+		if (!buffer_jbd(bh) || bh2jh(bh) != jh
+			|| jh->b_transaction != commit_transaction
+			|| jh->b_jlist != BJ_SyncData) {
+			jbd_unlock_bh_state(bh);
+			if (locked)
+				unlock_buffer(bh);
+			BUFFER_TRACE(bh, "already cleaned up");
+			release_data_buffer(bh);
+			continue;
+		}
+		if (locked && test_clear_buffer_dirty(bh)) {
+			BUFFER_TRACE(bh, "needs writeout, adding to array");
+			wbuf[bufs++] = bh;
+			__journal_file_buffer(jh, commit_transaction,
+						BJ_Locked);
+			jbd_unlock_bh_state(bh);
+			if (bufs == journal->j_wbufsize) {
+				spin_unlock(&journal->j_list_lock);
+				trace_jbd_do_submit_data(journal,
+						     commit_transaction);
+				journal_do_submit_data(wbuf, bufs, write_op);
+				bufs = 0;
+				goto write_out_data;
+			}
+		} else if (!locked && buffer_locked(bh)) {
+			__journal_file_buffer(jh, commit_transaction,
+						BJ_Locked);
+			jbd_unlock_bh_state(bh);
+			put_bh(bh);
+		} else {
+			BUFFER_TRACE(bh, "writeout complete: unfile");
+			if (unlikely(!buffer_uptodate(bh)))
+				err = -EIO;
+			__journal_unfile_buffer(jh);
+			jbd_unlock_bh_state(bh);
+			if (locked)
+				unlock_buffer(bh);
+			release_data_buffer(bh);
+		}
+
+		if (need_resched() || spin_needbreak(&journal->j_list_lock)) {
+			spin_unlock(&journal->j_list_lock);
+			goto write_out_data;
+		}
+	}
+	spin_unlock(&journal->j_list_lock);
+	trace_jbd_do_submit_data(journal, commit_transaction);
+	journal_do_submit_data(wbuf, bufs, write_op);
+
+	return err;
+}
+
+/*
+ * journal_commit_transaction
+ *
+ * The primary function for committing a transaction to the log.  This
+ * function is called by the journal thread to begin a complete commit.
+ */
+void journal_commit_transaction(journal_t *journal)
+{
+	transaction_t *commit_transaction;
+	struct journal_head *jh, *new_jh, *descriptor;
+	struct buffer_head **wbuf = journal->j_wbuf;
+	int bufs;
+	int flags;
+	int err;
+	unsigned int blocknr;
+	ktime_t start_time;
+	u64 commit_time;
+	char *tagp = NULL;
+	journal_header_t *header;
+	journal_block_tag_t *tag = NULL;
+	int space_left = 0;
+	int first_tag = 0;
+	int tag_flag;
+	int i;
+	struct blk_plug plug;
+	int write_op = WRITE;
+
+	/*
+	 * First job: lock down the current transaction and wait for
+	 * all outstanding updates to complete.
+	 */
+
+	/* Do we need to erase the effects of a prior journal_flush? */
+	if (journal->j_flags & JFS_FLUSHED) {
+		jbd_debug(3, "super block updated\n");
+		mutex_lock(&journal->j_checkpoint_mutex);
+		/*
+		 * We hold j_checkpoint_mutex so tail cannot change under us.
+		 * We don't need any special data guarantees for writing sb
+		 * since journal is empty and it is ok for write to be
+		 * flushed only with transaction commit.
+		 */
+		journal_update_sb_log_tail(journal, journal->j_tail_sequence,
+					   journal->j_tail, WRITE_SYNC);
+		mutex_unlock(&journal->j_checkpoint_mutex);
+	} else {
+		jbd_debug(3, "superblock not updated\n");
+	}
+
+	J_ASSERT(journal->j_running_transaction != NULL);
+	J_ASSERT(journal->j_committing_transaction == NULL);
+
+	commit_transaction = journal->j_running_transaction;
+
+	trace_jbd_start_commit(journal, commit_transaction);
+	jbd_debug(1, "JBD: starting commit of transaction %d\n",
+			commit_transaction->t_tid);
+
+	spin_lock(&journal->j_state_lock);
+	J_ASSERT(commit_transaction->t_state == T_RUNNING);
+	commit_transaction->t_state = T_LOCKED;
+
+	trace_jbd_commit_locking(journal, commit_transaction);
+	spin_lock(&commit_transaction->t_handle_lock);
+	while (commit_transaction->t_updates) {
+		DEFINE_WAIT(wait);
+
+		prepare_to_wait(&journal->j_wait_updates, &wait,
+					TASK_UNINTERRUPTIBLE);
+		if (commit_transaction->t_updates) {
+			spin_unlock(&commit_transaction->t_handle_lock);
+			spin_unlock(&journal->j_state_lock);
+			schedule();
+			spin_lock(&journal->j_state_lock);
+			spin_lock(&commit_transaction->t_handle_lock);
+		}
+		finish_wait(&journal->j_wait_updates, &wait);
+	}
+	spin_unlock(&commit_transaction->t_handle_lock);
+
+	J_ASSERT (commit_transaction->t_outstanding_credits <=
+			journal->j_max_transaction_buffers);
+
+	/*
+	 * First thing we are allowed to do is to discard any remaining
+	 * BJ_Reserved buffers.  Note, it is _not_ permissible to assume
+	 * that there are no such buffers: if a large filesystem
+	 * operation like a truncate needs to split itself over multiple
+	 * transactions, then it may try to do a journal_restart() while
+	 * there are still BJ_Reserved buffers outstanding.  These must
+	 * be released cleanly from the current transaction.
+	 *
+	 * In this case, the filesystem must still reserve write access
+	 * again before modifying the buffer in the new transaction, but
+	 * we do not require it to remember exactly which old buffers it
+	 * has reserved.  This is consistent with the existing behaviour
+	 * that multiple journal_get_write_access() calls to the same
+	 * buffer are perfectly permissible.
+	 */
+	while (commit_transaction->t_reserved_list) {
+		jh = commit_transaction->t_reserved_list;
+		JBUFFER_TRACE(jh, "reserved, unused: refile");
+		/*
+		 * A journal_get_undo_access()+journal_release_buffer() may
+		 * leave undo-committed data.
+		 */
+		if (jh->b_committed_data) {
+			struct buffer_head *bh = jh2bh(jh);
+
+			jbd_lock_bh_state(bh);
+			jbd_free(jh->b_committed_data, bh->b_size);
+			jh->b_committed_data = NULL;
+			jbd_unlock_bh_state(bh);
+		}
+		journal_refile_buffer(journal, jh);
+	}
+
+	/*
+	 * Now try to drop any written-back buffers from the journal's
+	 * checkpoint lists.  We do this *before* commit because it potentially
+	 * frees some memory
+	 */
+	spin_lock(&journal->j_list_lock);
+	__journal_clean_checkpoint_list(journal);
+	spin_unlock(&journal->j_list_lock);
+
+	jbd_debug (3, "JBD: commit phase 1\n");
+
+	/*
+	 * Clear revoked flag to reflect there is no revoked buffers
+	 * in the next transaction which is going to be started.
+	 */
+	journal_clear_buffer_revoked_flags(journal);
+
+	/*
+	 * Switch to a new revoke table.
+	 */
+	journal_switch_revoke_table(journal);
+
+	trace_jbd_commit_flushing(journal, commit_transaction);
+	commit_transaction->t_state = T_FLUSH;
+	journal->j_committing_transaction = commit_transaction;
+	journal->j_running_transaction = NULL;
+	start_time = ktime_get();
+	commit_transaction->t_log_start = journal->j_head;
+	wake_up(&journal->j_wait_transaction_locked);
+	spin_unlock(&journal->j_state_lock);
+
+	jbd_debug (3, "JBD: commit phase 2\n");
+
+	if (tid_geq(journal->j_commit_waited, commit_transaction->t_tid))
+		write_op = WRITE_SYNC;
+
+	/*
+	 * Now start flushing things to disk, in the order they appear
+	 * on the transaction lists.  Data blocks go first.
+	 */
+	blk_start_plug(&plug);
+	err = journal_submit_data_buffers(journal, commit_transaction,
+					  write_op);
+	blk_finish_plug(&plug);
+
+	/*
+	 * Wait for all previously submitted IO to complete.
+	 */
+	spin_lock(&journal->j_list_lock);
+	while (commit_transaction->t_locked_list) {
+		struct buffer_head *bh;
+
+		jh = commit_transaction->t_locked_list->b_tprev;
+		bh = jh2bh(jh);
+		get_bh(bh);
+		if (buffer_locked(bh)) {
+			spin_unlock(&journal->j_list_lock);
+			wait_on_buffer(bh);
+			spin_lock(&journal->j_list_lock);
+		}
+		if (unlikely(!buffer_uptodate(bh))) {
+			if (!trylock_page(bh->b_page)) {
+				spin_unlock(&journal->j_list_lock);
+				lock_page(bh->b_page);
+				spin_lock(&journal->j_list_lock);
+			}
+			if (bh->b_page->mapping)
+				set_bit(AS_EIO, &bh->b_page->mapping->flags);
+
+			unlock_page(bh->b_page);
+			SetPageError(bh->b_page);
+			err = -EIO;
+		}
+		if (!inverted_lock(journal, bh)) {
+			put_bh(bh);
+			spin_lock(&journal->j_list_lock);
+			continue;
+		}
+		if (buffer_jbd(bh) && bh2jh(bh) == jh &&
+		    jh->b_transaction == commit_transaction &&
+		    jh->b_jlist == BJ_Locked)
+			__journal_unfile_buffer(jh);
+		jbd_unlock_bh_state(bh);
+		release_data_buffer(bh);
+		cond_resched_lock(&journal->j_list_lock);
+	}
+	spin_unlock(&journal->j_list_lock);
+
+	if (err) {
+		char b[BDEVNAME_SIZE];
+
+		printk(KERN_WARNING
+			"JBD: Detected IO errors while flushing file data "
+			"on %s\n", bdevname(journal->j_fs_dev, b));
+		if (journal->j_flags & JFS_ABORT_ON_SYNCDATA_ERR)
+			journal_abort(journal, err);
+		err = 0;
+	}
+
+	blk_start_plug(&plug);
+
+	journal_write_revoke_records(journal, commit_transaction, write_op);
+
+	/*
+	 * If we found any dirty or locked buffers, then we should have
+	 * looped back up to the write_out_data label.  If there weren't
+	 * any then journal_clean_data_list should have wiped the list
+	 * clean by now, so check that it is in fact empty.
+	 */
+	J_ASSERT (commit_transaction->t_sync_datalist == NULL);
+
+	jbd_debug (3, "JBD: commit phase 3\n");
+
+	/*
+	 * Way to go: we have now written out all of the data for a
+	 * transaction!  Now comes the tricky part: we need to write out
+	 * metadata.  Loop over the transaction's entire buffer list:
+	 */
+	spin_lock(&journal->j_state_lock);
+	commit_transaction->t_state = T_COMMIT;
+	spin_unlock(&journal->j_state_lock);
+
+	trace_jbd_commit_logging(journal, commit_transaction);
+	J_ASSERT(commit_transaction->t_nr_buffers <=
+		 commit_transaction->t_outstanding_credits);
+
+	descriptor = NULL;
+	bufs = 0;
+	while (commit_transaction->t_buffers) {
+
+		/* Find the next buffer to be journaled... */
+
+		jh = commit_transaction->t_buffers;
+
+		/* If we're in abort mode, we just un-journal the buffer and
+		   release it. */
+
+		if (is_journal_aborted(journal)) {
+			clear_buffer_jbddirty(jh2bh(jh));
+			JBUFFER_TRACE(jh, "journal is aborting: refile");
+			journal_refile_buffer(journal, jh);
+			/* If that was the last one, we need to clean up
+			 * any descriptor buffers which may have been
+			 * already allocated, even if we are now
+			 * aborting. */
+			if (!commit_transaction->t_buffers)
+				goto start_journal_io;
+			continue;
+		}
+
+		/* Make sure we have a descriptor block in which to
+		   record the metadata buffer. */
+
+		if (!descriptor) {
+			struct buffer_head *bh;
+
+			J_ASSERT (bufs == 0);
+
+			jbd_debug(4, "JBD: get descriptor\n");
+
+			descriptor = journal_get_descriptor_buffer(journal);
+			if (!descriptor) {
+				journal_abort(journal, -EIO);
+				continue;
+			}
+
+			bh = jh2bh(descriptor);
+			jbd_debug(4, "JBD: got buffer %llu (%p)\n",
+				(unsigned long long)bh->b_blocknr, bh->b_data);
+			header = (journal_header_t *)&bh->b_data[0];
+			header->h_magic     = cpu_to_be32(JFS_MAGIC_NUMBER);
+			header->h_blocktype = cpu_to_be32(JFS_DESCRIPTOR_BLOCK);
+			header->h_sequence  = cpu_to_be32(commit_transaction->t_tid);
+
+			tagp = &bh->b_data[sizeof(journal_header_t)];
+			space_left = bh->b_size - sizeof(journal_header_t);
+			first_tag = 1;
+			set_buffer_jwrite(bh);
+			set_buffer_dirty(bh);
+			wbuf[bufs++] = bh;
+
+			/* Record it so that we can wait for IO
+                           completion later */
+			BUFFER_TRACE(bh, "ph3: file as descriptor");
+			journal_file_buffer(descriptor, commit_transaction,
+					BJ_LogCtl);
+		}
+
+		/* Where is the buffer to be written? */
+
+		err = journal_next_log_block(journal, &blocknr);
+		/* If the block mapping failed, just abandon the buffer
+		   and repeat this loop: we'll fall into the
+		   refile-on-abort condition above. */
+		if (err) {
+			journal_abort(journal, err);
+			continue;
+		}
+
+		/*
+		 * start_this_handle() uses t_outstanding_credits to determine
+		 * the free space in the log, but this counter is changed
+		 * by journal_next_log_block() also.
+		 */
+		commit_transaction->t_outstanding_credits--;
+
+		/* Bump b_count to prevent truncate from stumbling over
+                   the shadowed buffer!  @@@ This can go if we ever get
+                   rid of the BJ_IO/BJ_Shadow pairing of buffers. */
+		get_bh(jh2bh(jh));
+
+		/* Make a temporary IO buffer with which to write it out
+                   (this will requeue both the metadata buffer and the
+                   temporary IO buffer). new_bh goes on BJ_IO*/
+
+		set_buffer_jwrite(jh2bh(jh));
+		/*
+		 * akpm: journal_write_metadata_buffer() sets
+		 * new_bh->b_transaction to commit_transaction.
+		 * We need to clean this up before we release new_bh
+		 * (which is of type BJ_IO)
+		 */
+		JBUFFER_TRACE(jh, "ph3: write metadata");
+		flags = journal_write_metadata_buffer(commit_transaction,
+						      jh, &new_jh, blocknr);
+		set_buffer_jwrite(jh2bh(new_jh));
+		wbuf[bufs++] = jh2bh(new_jh);
+
+		/* Record the new block's tag in the current descriptor
+                   buffer */
+
+		tag_flag = 0;
+		if (flags & 1)
+			tag_flag |= JFS_FLAG_ESCAPE;
+		if (!first_tag)
+			tag_flag |= JFS_FLAG_SAME_UUID;
+
+		tag = (journal_block_tag_t *) tagp;
+		tag->t_blocknr = cpu_to_be32(jh2bh(jh)->b_blocknr);
+		tag->t_flags = cpu_to_be32(tag_flag);
+		tagp += sizeof(journal_block_tag_t);
+		space_left -= sizeof(journal_block_tag_t);
+
+		if (first_tag) {
+			memcpy (tagp, journal->j_uuid, 16);
+			tagp += 16;
+			space_left -= 16;
+			first_tag = 0;
+		}
+
+		/* If there's no more to do, or if the descriptor is full,
+		   let the IO rip! */
+
+		if (bufs == journal->j_wbufsize ||
+		    commit_transaction->t_buffers == NULL ||
+		    space_left < sizeof(journal_block_tag_t) + 16) {
+
+			jbd_debug(4, "JBD: Submit %d IOs\n", bufs);
+
+			/* Write an end-of-descriptor marker before
+                           submitting the IOs.  "tag" still points to
+                           the last tag we set up. */
+
+			tag->t_flags |= cpu_to_be32(JFS_FLAG_LAST_TAG);
+
+start_journal_io:
+			for (i = 0; i < bufs; i++) {
+				struct buffer_head *bh = wbuf[i];
+				lock_buffer(bh);
+				clear_buffer_dirty(bh);
+				set_buffer_uptodate(bh);
+				bh->b_end_io = journal_end_buffer_io_sync;
+				/*
+				 * In data=journal mode, here we can end up
+				 * writing pagecache data that might be
+				 * mmapped. Since we can't afford to clean the
+				 * page and set PageWriteback (see the comment
+				 * near the other use of _submit_bh()), the
+				 * data can change while the write is in
+				 * flight.  Tell the block layer to bounce the
+				 * bio pages if stable pages are required.
+				 */
+				_submit_bh(write_op, bh, 1 << BIO_SNAP_STABLE);
+			}
+			cond_resched();
+
+			/* Force a new descriptor to be generated next
+                           time round the loop. */
+			descriptor = NULL;
+			bufs = 0;
+		}
+	}
+
+	blk_finish_plug(&plug);
+
+	/* Lo and behold: we have just managed to send a transaction to
+           the log.  Before we can commit it, wait for the IO so far to
+           complete.  Control buffers being written are on the
+           transaction's t_log_list queue, and metadata buffers are on
+           the t_iobuf_list queue.
+
+	   Wait for the buffers in reverse order.  That way we are
+	   less likely to be woken up until all IOs have completed, and
+	   so we incur less scheduling load.
+	*/
+
+	jbd_debug(3, "JBD: commit phase 4\n");
+
+	/*
+	 * akpm: these are BJ_IO, and j_list_lock is not needed.
+	 * See __journal_try_to_free_buffer.
+	 */
+wait_for_iobuf:
+	while (commit_transaction->t_iobuf_list != NULL) {
+		struct buffer_head *bh;
+
+		jh = commit_transaction->t_iobuf_list->b_tprev;
+		bh = jh2bh(jh);
+		if (buffer_locked(bh)) {
+			wait_on_buffer(bh);
+			goto wait_for_iobuf;
+		}
+		if (cond_resched())
+			goto wait_for_iobuf;
+
+		if (unlikely(!buffer_uptodate(bh)))
+			err = -EIO;
+
+		clear_buffer_jwrite(bh);
+
+		JBUFFER_TRACE(jh, "ph4: unfile after journal write");
+		journal_unfile_buffer(journal, jh);
+
+		/*
+		 * ->t_iobuf_list should contain only dummy buffer_heads
+		 * which were created by journal_write_metadata_buffer().
+		 */
+		BUFFER_TRACE(bh, "dumping temporary bh");
+		journal_put_journal_head(jh);
+		__brelse(bh);
+		J_ASSERT_BH(bh, atomic_read(&bh->b_count) == 0);
+		free_buffer_head(bh);
+
+		/* We also have to unlock and free the corresponding
+                   shadowed buffer */
+		jh = commit_transaction->t_shadow_list->b_tprev;
+		bh = jh2bh(jh);
+		clear_buffer_jwrite(bh);
+		J_ASSERT_BH(bh, buffer_jbddirty(bh));
+
+		/* The metadata is now released for reuse, but we need
+                   to remember it against this transaction so that when
+                   we finally commit, we can do any checkpointing
+                   required. */
+		JBUFFER_TRACE(jh, "file as BJ_Forget");
+		journal_file_buffer(jh, commit_transaction, BJ_Forget);
+		/*
+		 * Wake up any transactions which were waiting for this
+		 * IO to complete. The barrier must be here so that changes
+		 * by journal_file_buffer() take effect before wake_up_bit()
+		 * does the waitqueue check.
+		 */
+		smp_mb();
+		wake_up_bit(&bh->b_state, BH_Unshadow);
+		JBUFFER_TRACE(jh, "brelse shadowed buffer");
+		__brelse(bh);
+	}
+
+	J_ASSERT (commit_transaction->t_shadow_list == NULL);
+
+	jbd_debug(3, "JBD: commit phase 5\n");
+
+	/* Here we wait for the revoke record and descriptor record buffers */
+ wait_for_ctlbuf:
+	while (commit_transaction->t_log_list != NULL) {
+		struct buffer_head *bh;
+
+		jh = commit_transaction->t_log_list->b_tprev;
+		bh = jh2bh(jh);
+		if (buffer_locked(bh)) {
+			wait_on_buffer(bh);
+			goto wait_for_ctlbuf;
+		}
+		if (cond_resched())
+			goto wait_for_ctlbuf;
+
+		if (unlikely(!buffer_uptodate(bh)))
+			err = -EIO;
+
+		BUFFER_TRACE(bh, "ph5: control buffer writeout done: unfile");
+		clear_buffer_jwrite(bh);
+		journal_unfile_buffer(journal, jh);
+		journal_put_journal_head(jh);
+		__brelse(bh);		/* One for getblk */
+		/* AKPM: bforget here */
+	}
+
+	if (err)
+		journal_abort(journal, err);
+
+	jbd_debug(3, "JBD: commit phase 6\n");
+
+	/* All metadata is written, now write commit record and do cleanup */
+	spin_lock(&journal->j_state_lock);
+	J_ASSERT(commit_transaction->t_state == T_COMMIT);
+	commit_transaction->t_state = T_COMMIT_RECORD;
+	spin_unlock(&journal->j_state_lock);
+
+	if (journal_write_commit_record(journal, commit_transaction))
+		err = -EIO;
+
+	if (err)
+		journal_abort(journal, err);
+
+	/* End of a transaction!  Finally, we can do checkpoint
+           processing: any buffers committed as a result of this
+           transaction can be removed from any checkpoint list it was on
+           before. */
+
+	jbd_debug(3, "JBD: commit phase 7\n");
+
+	J_ASSERT(commit_transaction->t_sync_datalist == NULL);
+	J_ASSERT(commit_transaction->t_buffers == NULL);
+	J_ASSERT(commit_transaction->t_checkpoint_list == NULL);
+	J_ASSERT(commit_transaction->t_iobuf_list == NULL);
+	J_ASSERT(commit_transaction->t_shadow_list == NULL);
+	J_ASSERT(commit_transaction->t_log_list == NULL);
+
+restart_loop:
+	/*
+	 * As there are other places (journal_unmap_buffer()) adding buffers
+	 * to this list we have to be careful and hold the j_list_lock.
+	 */
+	spin_lock(&journal->j_list_lock);
+	while (commit_transaction->t_forget) {
+		transaction_t *cp_transaction;
+		struct buffer_head *bh;
+		int try_to_free = 0;
+
+		jh = commit_transaction->t_forget;
+		spin_unlock(&journal->j_list_lock);
+		bh = jh2bh(jh);
+		/*
+		 * Get a reference so that bh cannot be freed before we are
+		 * done with it.
+		 */
+		get_bh(bh);
+		jbd_lock_bh_state(bh);
+		J_ASSERT_JH(jh,	jh->b_transaction == commit_transaction ||
+			jh->b_transaction == journal->j_running_transaction);
+
+		/*
+		 * If there is undo-protected committed data against
+		 * this buffer, then we can remove it now.  If it is a
+		 * buffer needing such protection, the old frozen_data
+		 * field now points to a committed version of the
+		 * buffer, so rotate that field to the new committed
+		 * data.
+		 *
+		 * Otherwise, we can just throw away the frozen data now.
+		 */
+		if (jh->b_committed_data) {
+			jbd_free(jh->b_committed_data, bh->b_size);
+			jh->b_committed_data = NULL;
+			if (jh->b_frozen_data) {
+				jh->b_committed_data = jh->b_frozen_data;
+				jh->b_frozen_data = NULL;
+			}
+		} else if (jh->b_frozen_data) {
+			jbd_free(jh->b_frozen_data, bh->b_size);
+			jh->b_frozen_data = NULL;
+		}
+
+		spin_lock(&journal->j_list_lock);
+		cp_transaction = jh->b_cp_transaction;
+		if (cp_transaction) {
+			JBUFFER_TRACE(jh, "remove from old cp transaction");
+			__journal_remove_checkpoint(jh);
+		}
+
+		/* Only re-checkpoint the buffer_head if it is marked
+		 * dirty.  If the buffer was added to the BJ_Forget list
+		 * by journal_forget, it may no longer be dirty and
+		 * there's no point in keeping a checkpoint record for
+		 * it. */
+
+		/*
+		 * A buffer which has been freed while still being journaled by
+		 * a previous transaction.
+		 */
+		if (buffer_freed(bh)) {
+			/*
+			 * If the running transaction is the one containing
+			 * "add to orphan" operation (b_next_transaction !=
+			 * NULL), we have to wait for that transaction to
+			 * commit before we can really get rid of the buffer.
+			 * So just clear b_modified to not confuse transaction
+			 * credit accounting and refile the buffer to
+			 * BJ_Forget of the running transaction. If the just
+			 * committed transaction contains "add to orphan"
+			 * operation, we can completely invalidate the buffer
+			 * now. We are rather throughout in that since the
+			 * buffer may be still accessible when blocksize <
+			 * pagesize and it is attached to the last partial
+			 * page.
+			 */
+			jh->b_modified = 0;
+			if (!jh->b_next_transaction) {
+				clear_buffer_freed(bh);
+				clear_buffer_jbddirty(bh);
+				clear_buffer_mapped(bh);
+				clear_buffer_new(bh);
+				clear_buffer_req(bh);
+				bh->b_bdev = NULL;
+			}
+		}
+
+		if (buffer_jbddirty(bh)) {
+			JBUFFER_TRACE(jh, "add to new checkpointing trans");
+			__journal_insert_checkpoint(jh, commit_transaction);
+			if (is_journal_aborted(journal))
+				clear_buffer_jbddirty(bh);
+		} else {
+			J_ASSERT_BH(bh, !buffer_dirty(bh));
+			/*
+			 * The buffer on BJ_Forget list and not jbddirty means
+			 * it has been freed by this transaction and hence it
+			 * could not have been reallocated until this
+			 * transaction has committed. *BUT* it could be
+			 * reallocated once we have written all the data to
+			 * disk and before we process the buffer on BJ_Forget
+			 * list.
+			 */
+			if (!jh->b_next_transaction)
+				try_to_free = 1;
+		}
+		JBUFFER_TRACE(jh, "refile or unfile freed buffer");
+		__journal_refile_buffer(jh);
+		jbd_unlock_bh_state(bh);
+		if (try_to_free)
+			release_buffer_page(bh);
+		else
+			__brelse(bh);
+		cond_resched_lock(&journal->j_list_lock);
+	}
+	spin_unlock(&journal->j_list_lock);
+	/*
+	 * This is a bit sleazy.  We use j_list_lock to protect transition
+	 * of a transaction into T_FINISHED state and calling
+	 * __journal_drop_transaction(). Otherwise we could race with
+	 * other checkpointing code processing the transaction...
+	 */
+	spin_lock(&journal->j_state_lock);
+	spin_lock(&journal->j_list_lock);
+	/*
+	 * Now recheck if some buffers did not get attached to the transaction
+	 * while the lock was dropped...
+	 */
+	if (commit_transaction->t_forget) {
+		spin_unlock(&journal->j_list_lock);
+		spin_unlock(&journal->j_state_lock);
+		goto restart_loop;
+	}
+
+	/* Done with this transaction! */
+
+	jbd_debug(3, "JBD: commit phase 8\n");
+
+	J_ASSERT(commit_transaction->t_state == T_COMMIT_RECORD);
+
+	commit_transaction->t_state = T_FINISHED;
+	J_ASSERT(commit_transaction == journal->j_committing_transaction);
+	journal->j_commit_sequence = commit_transaction->t_tid;
+	journal->j_committing_transaction = NULL;
+	commit_time = ktime_to_ns(ktime_sub(ktime_get(), start_time));
+
+	/*
+	 * weight the commit time higher than the average time so we don't
+	 * react too strongly to vast changes in commit time
+	 */
+	if (likely(journal->j_average_commit_time))
+		journal->j_average_commit_time = (commit_time*3 +
+				journal->j_average_commit_time) / 4;
+	else
+		journal->j_average_commit_time = commit_time;
+
+	spin_unlock(&journal->j_state_lock);
+
+	if (commit_transaction->t_checkpoint_list == NULL &&
+	    commit_transaction->t_checkpoint_io_list == NULL) {
+		__journal_drop_transaction(journal, commit_transaction);
+	} else {
+		if (journal->j_checkpoint_transactions == NULL) {
+			journal->j_checkpoint_transactions = commit_transaction;
+			commit_transaction->t_cpnext = commit_transaction;
+			commit_transaction->t_cpprev = commit_transaction;
+		} else {
+			commit_transaction->t_cpnext =
+				journal->j_checkpoint_transactions;
+			commit_transaction->t_cpprev =
+				commit_transaction->t_cpnext->t_cpprev;
+			commit_transaction->t_cpnext->t_cpprev =
+				commit_transaction;
+			commit_transaction->t_cpprev->t_cpnext =
+				commit_transaction;
+		}
+	}
+	spin_unlock(&journal->j_list_lock);
+
+	trace_jbd_end_commit(journal, commit_transaction);
+	jbd_debug(1, "JBD: commit %d complete, head %d\n",
+		  journal->j_commit_sequence, journal->j_tail_sequence);
+
+	wake_up(&journal->j_wait_done_commit);
+}