Index: linux-2.6.27.21-0.1/fs/ext4/mballoc.c
===================================================================
--- linux-2.6.27.21-0.1.orig/fs/ext4/mballoc.c
+++ linux-2.6.27.21-0.1/fs/ext4/mballoc.c
@@ -333,7 +333,7 @@
 static struct kmem_cache *ext4_pspace_cachep;
 static struct kmem_cache *ext4_ac_cachep;
 static struct kmem_cache *ext4_free_ext_cachep;
-static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
+static int ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
 					ext4_group_t group);
 static void ext4_mb_generate_from_freelist(struct super_block *sb, void *bitmap,
 						ext4_group_t group);
@@ -672,7 +672,7 @@ static void ext4_mb_mark_free_simple(str
 	}
 }
 
-static void ext4_mb_generate_buddy(struct super_block *sb,
+static int ext4_mb_generate_buddy(struct super_block *sb,
 				void *buddy, void *bitmap, ext4_group_t group)
 {
 	struct ext4_group_info *grp = ext4_get_group_info(sb, group);
@@ -704,14 +704,13 @@ static void ext4_mb_generate_buddy(struc
 	grp->bb_fragments = fragments;
 
 	if (free != grp->bb_free) {
-		ext4_grp_locked_error(sb, group,  __func__,
-			"EXT4-fs: group %u: %u blocks in bitmap, %u in gd\n",
-			group, free, grp->bb_free);
-		/*
-		 * If we intent to continue, we consider group descritor
-		 * corrupt and update bb_free using bitmap value
-		 */
-		grp->bb_free = free;
+		struct ext4_group_desc *gdp;
+		gdp = ext4_get_group_desc (sb, group, NULL);
+		ext4_grp_locked_error(sb, group, __func__,
+			"group %u: %u blocks in bitmap, %u in bb, "
+			"%u in gd\n", group, free, grp->bb_free,
+			ext4_free_blks_count(sb, gdp));
+		return -EIO;
 	}
 
 	clear_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &(grp->bb_state));
@@ -721,6 +720,8 @@ static void ext4_mb_generate_buddy(struc
 	EXT4_SB(sb)->s_mb_buddies_generated++;
 	EXT4_SB(sb)->s_mb_generation_time += period;
 	spin_unlock(&EXT4_SB(sb)->s_bal_lock);
+
+	return 0;
 }
 
 /* The buddy information is attached the buddy cache inode
@@ -850,7 +851,7 @@ static int ext4_mb_init_cache(struct pag
 	first_block = page->index * blocks_per_page;
 	/* init the page  */
 	memset(page_address(page), 0xff, PAGE_CACHE_SIZE);
-	for (i = 0; i < blocks_per_page; i++) {
+	for (i = 0; i < blocks_per_page && err == 0; i++) {
 		int group;
 		struct ext4_group_info *grinfo;
 
@@ -884,7 +885,7 @@ static int ext4_mb_init_cache(struct pag
 			 * incore got set to the group block bitmap below
 			 */
 			ext4_lock_group(sb, group);
-			ext4_mb_generate_buddy(sb, data, incore, group);
+			err = ext4_mb_generate_buddy(sb, data, incore, group);
 			ext4_unlock_group(sb, group);
 			incore = NULL;
 		} else {
@@ -898,7 +899,7 @@ static int ext4_mb_init_cache(struct pag
 			memcpy(data, bitmap, blocksize);
 
 			/* mark all preallocated blks used in in-core bitmap */
-			ext4_mb_generate_from_pa(sb, data, group);
+			err = ext4_mb_generate_from_pa(sb, data, group);
 			ext4_mb_generate_from_freelist(sb, data, group);
 			ext4_unlock_group(sb, group);
 
@@ -908,6 +909,7 @@ static int ext4_mb_init_cache(struct pag
 			incore = data;
 		}
 	}
+	if (likely(err == 0))
 	SetPageUptodate(page);
 
 out:
@@ -2217,7 +2219,10 @@ static int ext4_mb_seq_history_show(stru
 			hs->result.fe_start, hs->result.fe_len);
 		seq_printf(seq, "%-5u %-8u %-23s free\n",
 				hs->pid, hs->ino, buf2);
+	} else {
+		seq_printf(seq, "unknown op %d\n", hs->op);
 	}
+
 	return 0;
 }
 
@@ -2345,9 +2350,11 @@ static void *ext4_mb_seq_groups_next(str
 static int ext4_mb_seq_groups_show(struct seq_file *seq, void *v)
 {
 	struct super_block *sb = seq->private;
+	struct ext4_group_desc *gdp;
 	ext4_group_t group = (ext4_group_t) ((unsigned long) v);
 	int i;
 	int err;
+	unsigned free = 0;
 	struct ext4_buddy e4b;
 	struct sg {
 		struct ext4_group_info info;
@@ -2356,10 +2363,10 @@ static int ext4_mb_seq_groups_show(struc
 
 	group--;
 	if (group == 0)
-		seq_printf(seq, "#%-5s: %-5s %-5s %-5s "
+		seq_printf(seq, "#%-5s: %-5s %-5s %-5s %-5s %-5s"
 				"[ %-5s %-5s %-5s %-5s %-5s %-5s %-5s "
 				  "%-5s %-5s %-5s %-5s %-5s %-5s %-5s ]\n",
-			   "group", "free", "frags", "first",
+			   "group", "free", "frags", "first", "first", "pa",
 			   "2^0", "2^1", "2^2", "2^3", "2^4", "2^5", "2^6",
 			   "2^7", "2^8", "2^9", "2^10", "2^11", "2^12", "2^13");
 
@@ -2371,12 +2378,18 @@ static int ext4_mb_seq_groups_show(struc
 		seq_printf(seq, "#%-5u: I/O error\n", group);
 		return 0;
 	}
+
+	gdp = ext4_get_group_desc(sb, group, NULL);
+	if (gdp != NULL)
+		free = ext4_free_blks_count(sb, gdp);
+
 	ext4_lock_group(sb, group);
 	memcpy(&sg, ext4_get_group_info(sb, group), i);
 	ext4_unlock_group(sb, group);
 	ext4_mb_release_desc(&e4b);
 
-	seq_printf(seq, "#%-5u: %-5u %-5u %-5u [", group, sg.info.bb_free,
+	seq_printf(seq, "#%-5u: %-5u %-5u %-5u %-5u [", group,
+			sg.info.bb_free, free,
 			sg.info.bb_fragments, sg.info.bb_first_free);
 	for (i = 0; i <= 13; i++)
 		seq_printf(seq, " %-5u", i <= sb->s_blocksize_bits + 1 ?
@@ -2474,6 +2487,7 @@ ext4_mb_store_history(struct ext4_alloca
 	h.tail = ac->ac_tail;
 	h.buddy = ac->ac_buddy;
 	h.merged = 0;
+	h.cr = ac->ac_criteria;
 	if (ac->ac_op == EXT4_MB_HISTORY_ALLOC) {
 		if (ac->ac_g_ex.fe_start == ac->ac_b_ex.fe_start &&
 				ac->ac_g_ex.fe_group == ac->ac_b_ex.fe_group)
@@ -3695,22 +3709,67 @@ static void ext4_mb_generate_from_freeli
 }
 
 /*
+ * check free blocks in bitmap match free block in group descriptor
+ * do this before taking preallocated blocks into account to be able
+ * to detect on-disk corruptions. The group lock should be hold by the
+ * caller.
+ */
+int ext4_mb_check_ondisk_bitmap(struct super_block *sb, void *bitmap,
+				struct ext4_group_desc *gdp, int group)
+{
+	unsigned short max = EXT4_BLOCKS_PER_GROUP(sb);
+	unsigned short i, first, free = 0;
+
+	i = mb_find_next_zero_bit(bitmap, max, 0);
+
+	while (i < max) {
+		first = i;
+		i = mb_find_next_bit(bitmap, max, i);
+		if (i > max)
+			i = max;
+		free += i - first;
+		if (i < max)
+			i = mb_find_next_zero_bit(bitmap, max, i);
+	}
+
+	if (free != ext4_free_blks_count(sb, gdp)) {
+		ext4_error(sb, __FUNCTION__, "on-disk bitmap for group %d"
+			"corrupted: %u blocks free in bitmap, %u - in gd\n",
+			group, free, ext4_free_blks_count(sb, gdp));
+		return -EIO;
+	}
+	return 0;
+}
+
+/*
  * the function goes through all preallocation in this group and marks them
  * used in in-core bitmap. buddy must be generated from this bitmap
  * Need to be called with ext4 group lock (ext4_lock_group)
  */
-static void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
+static int ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
 					ext4_group_t group)
 {
 	struct ext4_group_info *grp = ext4_get_group_info(sb, group);
 	struct ext4_prealloc_space *pa;
+	struct ext4_group_desc *gdp;
 	struct list_head *cur;
 	ext4_group_t groupnr;
 	ext4_grpblk_t start;
 	int preallocated = 0;
 	int count = 0;
+	int skip = 0;
+	int err;
 	int len;
 
+	gdp = ext4_get_group_desc (sb, group, NULL);
+	if (gdp == NULL)
+		return -EIO;
+
+	/* before applying preallocations, check bitmap consistency */
+	err = ext4_mb_check_ondisk_bitmap(sb, bitmap, gdp, group);
+	if (err)
+		return err;
+
 	/* all form of preallocation discards first load group,
 	 * so the only competing code is preallocation use.
 	 * we don't need any locking here
@@ -3720,8 +3778,10 @@ static void ext4_mb_generate_from_pa(str
 					     &groupnr, &start);
 		len = pa->pa_len;
 		spin_unlock(&pa->pa_lock);
-		if (unlikely(len == 0))
+		if (unlikely(len == 0)) {
+			skip++;
 			continue;
+		}
 		BUG_ON(groupnr != group);
 		mb_set_bits(sb_bgl_lock(EXT4_SB(sb), group),
 						bitmap, start, len);
@@ -3729,6 +3789,7 @@ static void ext4_mb_generate_from_pa(str
 		count++;
 	}
 	mb_debug("prellocated %u for group %u\n", preallocated, group);
+	return 0;
 }
 
 static void ext4_mb_pa_callback(struct rcu_head *head)
@@ -3978,6 +4039,7 @@ ext4_mb_release_inode_pa(struct ext4_bud
 		ac->ac_sb = sb;
 		ac->ac_inode = pa->pa_inode;
 		ac->ac_op = EXT4_MB_HISTORY_DISCARD;
+		ac->ac_o_ex.fe_len = 1;
 	}
 
 	while (bit < end) {
@@ -4260,7 +4322,7 @@ repeat:
 			__release(e4b->alloc_semp);
 			ext4_error(sb, __func__, "Error in loading buddy "
 					"information for %u\n", group);
-			continue;
+			return;
 		}
 
 		bitmap_bh = ext4_read_block_bitmap(sb, group);
Index: linux-2.6.27.21-0.1/fs/ext4/mballoc.h
===================================================================
--- linux-2.6.27.21-0.1.orig/fs/ext4/mballoc.h
+++ linux-2.6.27.21-0.1/fs/ext4/mballoc.h
@@ -92,7 +92,7 @@
 /*
  * for which requests use 2^N search using buddies
  */
-#define MB_DEFAULT_ORDER2_REQS		2
+#define MB_DEFAULT_ORDER2_REQS		8

 /*
  * default group prealloc size 512 blocks
@@ -219,7 +219,7 @@ struct ext4_mb_history {
 	__u16 tail;	/* what tail broke some buddy */
 	__u16 buddy;	/* buddy the tail ^^^ broke */
 	__u16 flags;
-	__u8 cr:3;	/* which phase the result extent was found at */
+	__u8 cr:8;	/* which phase the result extent was found at */
 	__u8 op:4;
 	__u8 merged:1;
 };