ext4: make the bitmap read routines return real error codes

Make the bitmap reaading routines return real error codes (EIO,
EFSCORRUPTED, EFSBADCRC) which can then be reflected back to
userspace for more precise diagnosis work.

In particular, this means that mballoc no longer claims that we're out
of memory if the block bitmaps become corrupt.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 41 insertions, 33 deletions

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 32184c16af16..ec0668a60678 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -191,6 +191,7 @@ static int ext4_init_block_bitmap(struct super_block *sb,
 	/* If checksum is bad mark all blocks used to prevent allocation
 	 * essentially implementing a per-group read-only flag. */
 	if (!ext4_group_desc_csum_verify(sb, block_group, gdp)) {
+		ext4_error(sb, "Checksum bad for group %u", block_group);
 		grp = ext4_get_group_info(sb, block_group);
 		if (!EXT4_MB_GRP_BBITMAP_CORRUPT(grp))
 			percpu_counter_sub(&sbi->s_freeclusters_counter,
@@ -360,42 +361,45 @@ static ext4_fsblk_t ext4_valid_block_bitmap(struct super_block *sb,
 	return 0;
 }
 
-static void ext4_validate_block_bitmap(struct super_block *sb,
-				       struct ext4_group_desc *desc,
-				       ext4_group_t block_group,
-				       struct buffer_head *bh)
+static int ext4_validate_block_bitmap(struct super_block *sb,
+				      struct ext4_group_desc *desc,
+				      ext4_group_t block_group,
+				      struct buffer_head *bh)
 {
 	ext4_fsblk_t	blk;
 	struct ext4_group_info *grp = ext4_get_group_info(sb, block_group);
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 
-	if (buffer_verified(bh) || EXT4_MB_GRP_BBITMAP_CORRUPT(grp))
-		return;
+	if (buffer_verified(bh))
+		return 0;
+	if (EXT4_MB_GRP_BBITMAP_CORRUPT(grp))
+		return -EFSCORRUPTED;
 
 	ext4_lock_group(sb, block_group);
-	blk = ext4_valid_block_bitmap(sb, desc, block_group, bh);
-	if (unlikely(blk != 0)) {
+	if (unlikely(!ext4_block_bitmap_csum_verify(sb, block_group,
+			desc, bh))) {
 		ext4_unlock_group(sb, block_group);
-		ext4_error(sb, "bg %u: block %llu: invalid block bitmap",
-			   block_group, blk);
+		ext4_error(sb, "bg %u: bad block bitmap checksum", block_group);
 		if (!EXT4_MB_GRP_BBITMAP_CORRUPT(grp))
 			percpu_counter_sub(&sbi->s_freeclusters_counter,
 					   grp->bb_free);
 		set_bit(EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT, &grp->bb_state);
-		return;
+		return -EFSBADCRC;
 	}
-	if (unlikely(!ext4_block_bitmap_csum_verify(sb, block_group,
-			desc, bh))) {
+	blk = ext4_valid_block_bitmap(sb, desc, block_group, bh);
+	if (unlikely(blk != 0)) {
 		ext4_unlock_group(sb, block_group);
-		ext4_error(sb, "bg %u: bad block bitmap checksum", block_group);
+		ext4_error(sb, "bg %u: block %llu: invalid block bitmap",
+			   block_group, blk);
 		if (!EXT4_MB_GRP_BBITMAP_CORRUPT(grp))
 			percpu_counter_sub(&sbi->s_freeclusters_counter,
 					   grp->bb_free);
 		set_bit(EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT, &grp->bb_state);
-		return;
+		return -EFSCORRUPTED;
 	}
 	set_buffer_verified(bh);
 	ext4_unlock_group(sb, block_group);
+	return 0;
 }
 
 /**
@@ -414,17 +418,18 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 	struct ext4_group_desc *desc;
 	struct buffer_head *bh;
 	ext4_fsblk_t bitmap_blk;
+	int err;
 
 	desc = ext4_get_group_desc(sb, block_group, NULL);
 	if (!desc)
-		return NULL;
+		return ERR_PTR(-EFSCORRUPTED);
 	bitmap_blk = ext4_block_bitmap(sb, desc);
 	bh = sb_getblk(sb, bitmap_blk);
 	if (unlikely(!bh)) {
 		ext4_error(sb, "Cannot get buffer for block bitmap - "
 			   "block_group = %u, block_bitmap = %llu",
 			   block_group, bitmap_blk);
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 	}
 
 	if (bitmap_uptodate(bh))
@@ -437,7 +442,6 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 	}
 	ext4_lock_group(sb, block_group);
 	if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
-		int err;
 
 		err = ext4_init_block_bitmap(sb, bh, block_group, desc);
 		set_bitmap_uptodate(bh);
@@ -445,7 +449,7 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 		ext4_unlock_group(sb, block_group);
 		unlock_buffer(bh);
 		if (err)
-			ext4_error(sb, "Checksum bad for grp %u", block_group);
+			goto out;
 		goto verify;
 	}
 	ext4_unlock_group(sb, block_group);
@@ -468,11 +472,13 @@ ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
 	submit_bh(READ | REQ_META | REQ_PRIO, bh);
 	return bh;
 verify:
-	ext4_validate_block_bitmap(sb, desc, block_group, bh);
-	if (buffer_verified(bh))
-		return bh;
+	err = ext4_validate_block_bitmap(sb, desc, block_group, bh);
+	if (err)
+		goto out;
+	return bh;
+out:
 	put_bh(bh);
-	return NULL;
+	return ERR_PTR(err);
 }
 
 /* Returns 0 on success, 1 on error */
@@ -485,32 +491,32 @@ int ext4_wait_block_bitmap(struct super_block *sb, ext4_group_t block_group,
 		return 0;
 	desc = ext4_get_group_desc(sb, block_group, NULL);
 	if (!desc)
-		return 1;
+		return -EFSCORRUPTED;
 	wait_on_buffer(bh);
 	if (!buffer_uptodate(bh)) {
 		ext4_error(sb, "Cannot read block bitmap - "
 			   "block_group = %u, block_bitmap = %llu",
 			   block_group, (unsigned long long) bh->b_blocknr);
-		return 1;
+		return -EIO;
 	}
 	clear_buffer_new(bh);
 	/* Panic or remount fs read-only if block bitmap is invalid */
-	ext4_validate_block_bitmap(sb, desc, block_group, bh);
-	/* ...but check for error just in case errors=continue. */
-	return !buffer_verified(bh);
+	return ext4_validate_block_bitmap(sb, desc, block_group, bh);
 }
 
 struct buffer_head *
 ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
 {
 	struct buffer_head *bh;
+	int err;
 
 	bh = ext4_read_block_bitmap_nowait(sb, block_group);
-	if (!bh)
-		return NULL;
-	if (ext4_wait_block_bitmap(sb, block_group, bh)) {
+	if (IS_ERR(bh))
+		return bh;
+	err = ext4_wait_block_bitmap(sb, block_group, bh);
+	if (err) {
 		put_bh(bh);
-		return NULL;
+		return ERR_PTR(err);
 	}
 	return bh;
 }
@@ -681,8 +687,10 @@ ext4_fsblk_t ext4_count_free_clusters(struct super_block *sb)
 			desc_count += ext4_free_group_clusters(sb, gdp);
 		brelse(bitmap_bh);
 		bitmap_bh = ext4_read_block_bitmap(sb, i);
-		if (bitmap_bh == NULL)
+		if (IS_ERR(bitmap_bh)) {
+			bitmap_bh = NULL;
 			continue;
+		}
 
 		x = ext4_count_free(bitmap_bh->b_data,
 				    EXT4_CLUSTERS_PER_GROUP(sb) / 8);