e2fsck: decrement bad count _after_ remapping a duplicate block

Decrement the bad count *after* we've shown that (a) we can allocate a
replacement block and (b) remap the file block.  Unfortunately,
the only way to tell if the remapping succeeded is to wait until the
next clone_file_block() call or block_iterate3() returns.

Otherwise, there's a corruption error: we decrease the badcount once in
preparation to remap, then the remap fails (either we can't find a
replacement block or we have to split the extent tree and can't find a
new extent block), so we delete the file, which decreases the badcount
on the block a second time.  Later on e2fsck will think that it's
straightened out all the duplicate blocks, which isn't true.

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

e2fsck/pass1b.c

@@ -725,8 +725,30 @@ struct clone_struct {
 	char	*buf;
 	e2fsck_t ctx;
 	struct ext2_inode	*inode;
+
+	struct dup_cluster *save_dup_cluster;
+	blk64_t save_blocknr;
 };
 
+/*
+ * Decrement the bad count *after* we've shown that (a) we can allocate a
+ * replacement block and (b) remap the file blocks.  Unfortunately, there's no
+ * way to find out if the remap succeeded until either the next
+ * clone_file_block() call (an error when remapping the block after returning
+ * BLOCK_CHANGED will halt the iteration) or after block_iterate() returns.
+ * Otherwise, it's possible that we decrease the badcount once in preparation
+ * to remap, then the remap fails (either we can't find a replacement block or
+ * we have to split the extent tree and can't find a new extent block), so we
+ * delete the file, which decreases the badcount again.
+ */
+static void deferred_dec_badcount(struct clone_struct *cs)
+{
+	if (!cs->save_dup_cluster)
+		return;
+	decrement_badcount(cs->ctx, cs->save_blocknr, cs->save_dup_cluster);
+	cs->save_dup_cluster = NULL;
+}
+
 static int clone_file_block(ext2_filsys fs,
 			    blk64_t	*block_nr,
 			    e2_blkcnt_t blockcnt,
@@ -734,7 +756,7 @@ static int clone_file_block(ext2_filsys fs,
 			    int ref_offset EXT2FS_ATTR((unused)),
 			    void *priv_data)
 {
-	struct dup_cluster *p;
+	struct dup_cluster *p = NULL;
 	blk64_t	new_block;
 	errcode_t	retval;
 	struct clone_struct *cs = (struct clone_struct *) priv_data;
@@ -744,6 +766,7 @@ static int clone_file_block(ext2_filsys fs,
 	int is_meta = 0;
 
 	ctx = cs->ctx;
+	deferred_dec_badcount(cs);
 
 	if (HOLE_BLKADDR(*block_nr))
 		return 0;
@@ -768,8 +791,6 @@ static int clone_file_block(ext2_filsys fs,
 		}
 
 		p = (struct dup_cluster *) dnode_get(n);
-		if (!is_meta)
-			decrement_badcount(ctx, *block_nr, p);
 
 		cs->dup_cluster = c;
 		/*
@@ -819,6 +840,8 @@ cluster_alloc_ok:
 			cs->errcode = retval;
 			return BLOCK_ABORT;
 		}
+		cs->save_dup_cluster = (is_meta ? NULL : p);
+		cs->save_blocknr = *block_nr;
 		*block_nr = new_block;
 		ext2fs_mark_block_bitmap2(ctx->block_found_map, new_block);
 		ext2fs_mark_block_bitmap2(fs->block_map, new_block);
@@ -848,6 +871,8 @@ static errcode_t clone_file(e2fsck_t ctx, ext2_ino_t ino,
 	cs.ctx = ctx;
 	cs.ino = ino;
 	cs.inode = &dp->inode;
+	cs.save_dup_cluster = NULL;
+	cs.save_blocknr = 0;
 	retval = ext2fs_get_mem(fs->blocksize, &cs.buf);
 	if (retval)
 		return retval;
@@ -860,6 +885,7 @@ static errcode_t clone_file(e2fsck_t ctx, ext2_ino_t ino,
 	if (ext2fs_inode_has_valid_blocks2(fs, &dp->inode))
 		pctx.errcode = ext2fs_block_iterate3(fs, ino, 0, block_buf,
 						     clone_file_block, &cs);
+	deferred_dec_badcount(&cs);
 	ext2fs_mark_bb_dirty(fs);
 	if (pctx.errcode) {
 		fix_problem(ctx, PR_1B_BLOCK_ITERATE, &pctx);

tests/f_cloneblock_alloc_error/expect.1

@@ -0,0 +1,36 @@
+Pass 1: Checking inodes, blocks, and sizes
+Inode 12, i_size is 0, should be 2015232.  Fix? yes
+
+
+Running additional passes to resolve blocks claimed by more than one inode...
+Pass 1B: Rescanning for multiply-claimed blocks
+Multiply-claimed block(s) in inode 13: 8
+Multiply-claimed block(s) in inode 14: 8
+Pass 1C: Scanning directories for inodes with multiply-claimed blocks
+Pass 1D: Reconciling multiply-claimed blocks
+(There are 2 inodes containing multiply-claimed blocks.)
+
+File /b (inode #13, mod time Wed Jan 21 03:41:55 2015) 
+  has 1 multiply-claimed block(s), shared with 1 file(s):
+	/c (inode #14, mod time Wed Jan 21 03:42:37 2015)
+Clone multiply-claimed blocks? yes
+
+clone_file: Could not allocate block in ext2 filesystem returned from clone_file_block
+Couldn't clone file: Could not allocate block in ext2 filesystem
+Delete file? yes
+
+File /c (inode #14, mod time Wed Jan 21 03:42:37 2015) 
+  has 1 multiply-claimed block(s), shared with 1 file(s):
+	/b (inode #13, mod time Wed Jan 21 03:41:55 2015)
+Multiply-claimed blocks already reassigned or cloned.
+
+Pass 2: Checking directory structure
+Entry 'b' in / (2) has deleted/unused inode 13.  Clear? yes
+
+Pass 3: Checking directory connectivity
+Pass 4: Checking reference counts
+Pass 5: Checking group summary information
+
+test_filesys: ***** FILE SYSTEM WAS MODIFIED *****
+test_filesys: 13/128 files (7.7% non-contiguous), 512/512 blocks
+Exit status is 1

tests/f_cloneblock_alloc_error/expect.2

@@ -0,0 +1,7 @@
+Pass 1: Checking inodes, blocks, and sizes
+Pass 2: Checking directory structure
+Pass 3: Checking directory connectivity
+Pass 4: Checking reference counts
+Pass 5: Checking group summary information
+test_filesys: 13/128 files (7.7% non-contiguous), 512/512 blocks
+Exit status is 0

tests/f_cloneblock_alloc_error/name

@@ -0,0 +1 @@
+decrement badcount after remapping duplicate block