Index: linux-stage/fs/ext4/ext4.h
===================================================================
--- linux-stage.orig/fs/ext4/ext4.h	2011-03-14 16:18:28.300241437 +0800
+++ linux-stage/fs/ext4/ext4.h	2011-03-14 16:33:17.056087375 +0800
@@ -1770,6 +1770,7 @@
 	ext4_grpblk_t	bb_free;	/* total free blocks */
 	ext4_grpblk_t	bb_fragments;	/* nr of freespace fragments */
 	struct          list_head bb_prealloc_list;
+	unsigned long   bb_prealloc_nr;
 #ifdef DOUBLE_CHECK
 	void            *bb_bitmap;
 #endif
Index: linux-stage/fs/ext4/mballoc.c
===================================================================
--- linux-stage.orig/fs/ext4/mballoc.c	2011-03-14 16:18:28.336242149 +0800
+++ linux-stage/fs/ext4/mballoc.c	2011-03-14 16:33:27.072292006 +0800
@@ -337,7 +337,7 @@
 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);
@@ -659,7 +659,7 @@
 }
 
 static noinline_for_stack
-void ext4_mb_generate_buddy(struct super_block *sb,
+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);
@@ -691,14 +691,13 @@
 	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",
-			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_error(sb, "group %lu: %u blocks in bitmap, %u in bb, "
+			"%u in gd, %lu pa's\n", (long unsigned int)group,
+			free, grp->bb_free, ext4_free_blks_count(sb, gdp),
+			grp->bb_prealloc_nr);
+		return -EIO;
 	}
 
 	clear_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &(grp->bb_state));
@@ -708,6 +707,8 @@
 	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
@@ -839,7 +840,7 @@
 	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;
 
@@ -874,7 +875,7 @@
 			 * 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 {
@@ -888,7 +889,7 @@
 			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);
 
@@ -898,7 +899,8 @@
 			incore = data;
 		}
 	}
-	SetPageUptodate(page);
+	if (likely(err == 0))
+		SetPageUptodate(page);
 
 out:
 	if (bh) {
@@ -2142,9 +2144,11 @@
 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;
+	int free = 0;
 	struct ext4_buddy e4b;
 	struct sg {
 		struct ext4_group_info info;
@@ -2153,10 +2157,10 @@
 
 	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");
 
@@ -2167,13 +2171,20 @@
 		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,
-			sg.info.bb_fragments, sg.info.bb_first_free);
+	seq_printf(seq, "#%-5lu: %-5u %-5u %-5u %-5u %-5lu [",
+			(long unsigned int)group, sg.info.bb_free, free,
+			sg.info.bb_fragments, sg.info.bb_first_free,
+			sg.info.bb_prealloc_nr);
 	for (i = 0; i <= 13; i++)
 		seq_printf(seq, " %-5u", i <= sb->s_blocksize_bits + 1 ?
 				sg.info.bb_counters[i] : 0);
@@ -3354,23 +3365,68 @@
 }
 
 /*
+ * 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, "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 held
  */
 static noinline_for_stack
-void ext4_mb_generate_from_pa(struct super_block *sb, void *bitmap,
+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
@@ -3386,14 +3442,23 @@
 					     &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(bitmap, start, len);
 		preallocated += len;
 		count++;
 	}
+	if (count + skip != grp->bb_prealloc_nr) {
+		ext4_error(sb, "lost preallocations: "
+			   "count %d, bb_prealloc_nr %lu, skip %d\n",
+			   count, grp->bb_prealloc_nr, skip);
+		return -EIO;
+	}
 	mb_debug(1, "prellocated %u for group %u\n", preallocated, group);
+	return 0;
 }
 
 static void ext4_mb_pa_callback(struct rcu_head *head)
@@ -3452,6 +3517,7 @@
 	 */
 	ext4_lock_group(sb, grp);
 	list_del(&pa->pa_group_list);
+	ext4_get_group_info(sb, grp)->bb_prealloc_nr--;
 	ext4_unlock_group(sb, grp);
 
 	spin_lock(pa->pa_obj_lock);
@@ -3543,6 +3609,7 @@
 
 	ext4_lock_group(sb, ac->ac_b_ex.fe_group);
 	list_add(&pa->pa_group_list, &grp->bb_prealloc_list);
+	grp->bb_prealloc_nr++;
 	ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
 
 	spin_lock(pa->pa_obj_lock);
@@ -3604,6 +3671,7 @@
 
 	ext4_lock_group(sb, ac->ac_b_ex.fe_group);
 	list_add(&pa->pa_group_list, &grp->bb_prealloc_list);
+	grp->bb_prealloc_nr++;
 	ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
 
 	/*
@@ -3802,6 +3870,8 @@
 
 		spin_unlock(&pa->pa_lock);
 
+		BUG_ON(grp->bb_prealloc_nr == 0);
+		grp->bb_prealloc_nr--;
 		list_del(&pa->pa_group_list);
 		list_add(&pa->u.pa_tmp_list, &list);
 	}
@@ -3942,7 +4012,7 @@
 		if (err) {
 			ext4_error(sb, "Error loading buddy information for %u",
 					group);
-			continue;
+			return;
 		}
 
 		bitmap_bh = ext4_read_block_bitmap(sb, group);
@@ -3954,6 +4024,8 @@
 		}
 
 		ext4_lock_group(sb, group);
+		BUG_ON(e4b.bd_info->bb_prealloc_nr == 0);
+		e4b.bd_info->bb_prealloc_nr--;
 		list_del(&pa->pa_group_list);
 		ext4_mb_release_inode_pa(&e4b, bitmap_bh, pa, ac);
 		ext4_unlock_group(sb, group);
@@ -4227,6 +4299,7 @@
 		}
 		ext4_lock_group(sb, group);
 		list_del(&pa->pa_group_list);
+		ext4_get_group_info(sb, group)->bb_prealloc_nr--;
 		ext4_mb_release_group_pa(&e4b, pa, ac);
 		ext4_unlock_group(sb, group);
 
Index: linux-stage/fs/ext4/mballoc.h
===================================================================
--- linux-stage.orig/fs/ext4/mballoc.h	2011-03-14 16:18:26.670209322 +0800
+++ linux-stage/fs/ext4/mballoc.h	2011-03-14 16:32:50.859552482 +0800
@@ -88,7 +88,7 @@
 /*
  * 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