From: Eric Sandeen <sandeen@redhat.com>
Date: Thu, 19 Jun 2008 10:34:33 -0500
Subject: [fs] ext3: lighten up resize transaction requirements
Message-id: 485A7C89.5070004@redhat.com
O-Subject: [PATCH RHEL5.3] ext3: lighten up resize transaction requirements
Bugzilla: 425955
RH-Acked-by: Peter Staubach <staubach@redhat.com>
RH-Acked-by: Josef Bacik <jbacik@redhat.com>

This is for bug 425955: ext2online can't resize: No space left on device

It is a backport of a patch I wrote which has been upstream since last October.
(see git commit header below).  It is also in RHEL4.7 already.

Thanks,
-Eric

------------

From: Eric Sandeen <sandeen@redhat.com>
Date: Wed, 17 Oct 2007 06:30:28 +0000 (-0700)
Subject: ext3: lighten up resize transaction requirements
X-Git-Tag: v2.6.24-rc1~584
X-Git-Url: http://git.kernel.org/?p=linux%2Fkernel%2Fgit%2Ftorvalds%2Flinux-2.6.git;a=commitdiff_plain;h=1ad6ecf9146e85ccb4e0bce70b91a93f57145c72

ext3: lighten up resize transaction requirements

When resizing online, setup_new_group_blocks attempts to reserve a
potentially very large transaction, depending on the current filesystem
geometry.  For some journal sizes, there may not be enough room for this
transaction, and the online resize will fail.

The patch below resizes & restarts the transaction as necessary while
setting up the new group, and should work with even the smallest journal.

Tested with something like:

[root@newbox ~]# dd if=/dev/zero of=fsfile bs=1024 count=32768
[root@newbox ~]# mkfs.ext3 -b 1024 fsfile 16384
[root@newbox ~]# mount -o loop fsfile mnt/
[root@newbox ~]# resize2fs /dev/loop0
resize2fs 1.40.2 (12-Jul-2007)
Filesystem at /dev/loop0 is mounted on /root/mnt; on-line resizing required
old desc_blocks = 1, new_desc_blocks = 1
Performing an on-line resize of /dev/loop0 to 32768 (1k) blocks.
resize2fs: No space left on device While trying to add group #2
[root@newbox ~]# dmesg | tail -n 1
JBD: resize2fs wants too many credits (258 > 256)
[root@newbox ~]#

With the below change, it works.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Acked-by: Andreas Dilger <adilger@clusterfs.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/fs/ext3/resize.c b/fs/ext3/resize.c
index 11ea0f8..c1fefb9 100644
--- a/fs/ext3/resize.c
+++ b/fs/ext3/resize.c
@@ -156,6 +156,34 @@ static void mark_bitmap_end(int start_bit, int end_bit, char *bitmap)
 }
 
 /*
+ * If we have fewer than thresh credits, extend by EXT3_MAX_TRANS_DATA.
+ * If that fails, restart the transaction & regain write access for the
+ * buffer head which is used for block_bitmap modifications.
+ */
+static int extend_or_restart_transaction(handle_t *handle, int thresh,
+					 struct buffer_head *bh)
+{
+	int err;
+
+	if (handle->h_buffer_credits >= thresh)
+		return 0;
+
+	err = ext3_journal_extend(handle, EXT3_MAX_TRANS_DATA);
+	if (err < 0)
+		return err;
+	if (err) {
+		err = ext3_journal_restart(handle, EXT3_MAX_TRANS_DATA);
+		if (err)
+			return err;
+		err = ext3_journal_get_write_access(handle, bh);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+/*
  * Set up the block and inode bitmaps, and the inode table for the new group.
  * This doesn't need to be part of the main transaction, since we are only
  * changing blocks outside the actual filesystem.  We still do journaling to
@@ -177,8 +205,9 @@ static int setup_new_group_blocks(struct super_block *sb,
 	int i;
 	int err = 0, err2;
 
-	handle = ext3_journal_start_sb(sb, reserved_gdb + gdblocks +
-				       2 + sbi->s_itb_per_group);
+	/* This transaction may be extended/restarted along the way */
+	handle = ext3_journal_start_sb(sb, EXT3_MAX_TRANS_DATA);
+
 	if (IS_ERR(handle))
 		return PTR_ERR(handle);
 
@@ -205,6 +234,10 @@ static int setup_new_group_blocks(struct super_block *sb,
 
 		ext3_debug("update backup group %#04lx (+%d)\n", block, bit);
 
+		err = extend_or_restart_transaction(handle, 1, bh);
+		if (err)
+			goto exit_bh;
+
 		gdb = sb_getblk(sb, block);
 		if (!gdb) {
 			err = -EIO;
@@ -230,6 +263,10 @@ static int setup_new_group_blocks(struct super_block *sb,
 
 		ext3_debug("clear reserved block %#04lx (+%d)\n", block, bit);
 
+		err = extend_or_restart_transaction(handle, 1, bh);
+		if (err)
+			goto exit_bh;
+
 		if (IS_ERR(gdb = bclean(handle, sb, block))) {
 			err = PTR_ERR(bh);
 			goto exit_bh;
@@ -251,6 +288,11 @@ static int setup_new_group_blocks(struct super_block *sb,
 		struct buffer_head *it;
 
 		ext3_debug("clear inode block %#04lx (+%d)\n", block, bit);
+
+		err = extend_or_restart_transaction(handle, 1, bh);
+		if (err)
+			goto exit_bh;
+
 		if (IS_ERR(it = bclean(handle, sb, block))) {
 			err = PTR_ERR(it);
 			goto exit_bh;
@@ -259,6 +301,11 @@ static int setup_new_group_blocks(struct super_block *sb,
 		brelse(it);
 		ext3_set_bit(bit, bh->b_data);
 	}
+
+	err = extend_or_restart_transaction(handle, 2, bh);
+	if (err)
+		goto exit_bh;
+
 	mark_bitmap_end(input->blocks_count, EXT3_BLOCKS_PER_GROUP(sb),
 			bh->b_data);
 	ext3_journal_dirty_metadata(handle, bh);