ext4: fix punch hole on files with indirect mapping

Currently punch hole code on files with direct/indirect mapping has some
problems which may lead to a data loss. For example (from Jan Kara):

fallocate -n -p 10240000 4096

will punch the range 10240000 - 12632064 instead of the range 1024000 -
10244096.

Also the code is a bit weird and it's not using infrastructure provided
by indirect.c, but rather creating it's own way.

This patch fixes the issues as well as making the operation to run 4
times faster from my testing (punching out 60GB file). It uses similar
approach used in ext4_ind_truncate() which takes advantage of
ext4_free_branches() function.

Also rename the ext4_free_hole_blocks() to something more sensible, like
the equivalent we have for extent mapped files. Call it
ext4_ind_remove_space().

This has been tested mostly with fsx and some xfstests which are testing
punch hole but does not require unwritten extents which are not
supported with direct/indirect mapping. Not problems showed up even with
1024k block size.

CC: stable@vger.kernel.org
Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -2143,8 +2143,8 @@ extern ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb,
 extern int ext4_ind_calc_metadata_amount(struct inode *inode, sector_t lblock);
 extern int ext4_ind_trans_blocks(struct inode *inode, int nrblocks);
 extern void ext4_ind_truncate(handle_t *, struct inode *inode);
-extern int ext4_free_hole_blocks(handle_t *handle, struct inode *inode,
-				 ext4_lblk_t first, ext4_lblk_t stop);
+extern int ext4_ind_remove_space(handle_t *handle, struct inode *inode,
+				 ext4_lblk_t start, ext4_lblk_t end);
 
 /* ioctl.c */
 extern long ext4_ioctl(struct file *, unsigned int, unsigned long);

fs/ext4/indirect.c

@@ -1295,97 +1295,220 @@ void ext4_ind_truncate(handle_t *handle, struct inode *inode)
 	}
 }
 
-static int free_hole_blocks(handle_t *handle, struct inode *inode,
-			    struct buffer_head *parent_bh, __le32 *i_data,
-			    int level, ext4_lblk_t first,
-			    ext4_lblk_t count, int max)
+/**
+ *	ext4_ind_remove_space - remove space from the range
+ *	@handle: JBD handle for this transaction
+ *	@inode:	inode we are dealing with
+ *	@start:	First block to remove
+ *	@end:	One block after the last block to remove (exclusive)
+ *
+ *	Free the blocks in the defined range (end is exclusive endpoint of
+ *	range). This is used by ext4_punch_hole().
+ */
+int ext4_ind_remove_space(handle_t *handle, struct inode *inode,
+			  ext4_lblk_t start, ext4_lblk_t end)
 {
-	struct buffer_head *bh = NULL;
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	__le32 *i_data = ei->i_data;
 	int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
-	int ret = 0;
-	int i, inc;
-	ext4_lblk_t offset;
-	__le32 blk;
-
-	inc = 1 << ((EXT4_BLOCK_SIZE_BITS(inode->i_sb) - 2) * level);
-	for (i = 0, offset = 0; i < max; i++, i_data++, offset += inc) {
-		if (offset >= count + first)
-			break;
-		if (*i_data == 0 || (offset + inc) <= first)
-			continue;
-		blk = *i_data;
-		if (level > 0) {
-			ext4_lblk_t first2;
-			ext4_lblk_t count2;
+	ext4_lblk_t offsets[4], offsets2[4];
+	Indirect chain[4], chain2[4];
+	Indirect *partial, *partial2;
+	ext4_lblk_t max_block;
+	__le32 nr = 0, nr2 = 0;
+	int n = 0, n2 = 0;
+	unsigned blocksize = inode->i_sb->s_blocksize;
 
-			bh = sb_bread(inode->i_sb, le32_to_cpu(blk));
-			if (!bh) {
-				EXT4_ERROR_INODE_BLOCK(inode, le32_to_cpu(blk),
-						       "Read failure");
-				return -EIO;
-			}
-			if (first > offset) {
-				first2 = first - offset;
-				count2 = count;
+	max_block = (EXT4_SB(inode->i_sb)->s_bitmap_maxbytes + blocksize-1)
+					>> EXT4_BLOCK_SIZE_BITS(inode->i_sb);
+	if (end >= max_block)
+		end = max_block;
+	if ((start >= end) || (start > max_block))
+		return 0;
+
+	n = ext4_block_to_path(inode, start, offsets, NULL);
+	n2 = ext4_block_to_path(inode, end, offsets2, NULL);
+
+	BUG_ON(n > n2);
+
+	if ((n == 1) && (n == n2)) {
+		/* We're punching only within direct block range */
+		ext4_free_data(handle, inode, NULL, i_data + offsets[0],
+			       i_data + offsets2[0]);
+		return 0;
+	} else if (n2 > n) {
+		/*
+		 * Start and end are on a different levels so we're going to
+		 * free partial block at start, and partial block at end of
+		 * the range. If there are some levels in between then
+		 * do_indirects label will take care of that.
+		 */
+
+		if (n == 1) {
+			/*
+			 * Start is at the direct block level, free
+			 * everything to the end of the level.
+			 */
+			ext4_free_data(handle, inode, NULL, i_data + offsets[0],
+				       i_data + EXT4_NDIR_BLOCKS);
+			goto end_range;
+		}
+
+
+		partial = ext4_find_shared(inode, n, offsets, chain, &nr);
+		if (nr) {
+			if (partial == chain) {
+				/* Shared branch grows from the inode */
+				ext4_free_branches(handle, inode, NULL,
+					   &nr, &nr+1, (chain+n-1) - partial);
+				*partial->p = 0;
 			} else {
-				first2 = 0;
-				count2 = count - (offset - first);
+				/* Shared branch grows from an indirect block */
+				BUFFER_TRACE(partial->bh, "get_write_access");
+				ext4_free_branches(handle, inode, partial->bh,
+					partial->p,
+					partial->p+1, (chain+n-1) - partial);
 			}
-			ret = free_hole_blocks(handle, inode, bh,
-					       (__le32 *)bh->b_data, level - 1,
-					       first2, count2,
-					       inode->i_sb->s_blocksize >> 2);
-			if (ret) {
-				brelse(bh);
-				goto err;
+		}
+
+		/*
+		 * Clear the ends of indirect blocks on the shared branch
+		 * at the start of the range
+		 */
+		while (partial > chain) {
+			ext4_free_branches(handle, inode, partial->bh,
+				partial->p + 1,
+				(__le32 *)partial->bh->b_data+addr_per_block,
+				(chain+n-1) - partial);
+			BUFFER_TRACE(partial->bh, "call brelse");
+			brelse(partial->bh);
+			partial--;
+		}
+
+end_range:
+		partial2 = ext4_find_shared(inode, n2, offsets2, chain2, &nr2);
+		if (nr2) {
+			if (partial2 == chain2) {
+				/*
+				 * Remember, end is exclusive so here we're at
+				 * the start of the next level we're not going
+				 * to free. Everything was covered by the start
+				 * of the range.
+				 */
+				return 0;
+			} else {
+				/* Shared branch grows from an indirect block */
+				partial2--;
 			}
+		} else {
+			/*
+			 * ext4_find_shared returns Indirect structure which
+			 * points to the last element which should not be
+			 * removed by truncate. But this is end of the range
+			 * in punch_hole so we need to point to the next element
+			 */
+			partial2->p++;
 		}
-		if (level == 0 ||
-		    (bh && all_zeroes((__le32 *)bh->b_data,
-				      (__le32 *)bh->b_data + addr_per_block))) {
-			ext4_free_data(handle, inode, parent_bh,
-				       i_data, i_data + 1);
+
+		/*
+		 * Clear the ends of indirect blocks on the shared branch
+		 * at the end of the range
+		 */
+		while (partial2 > chain2) {
+			ext4_free_branches(handle, inode, partial2->bh,
+					   (__le32 *)partial2->bh->b_data,
+					   partial2->p,
+					   (chain2+n2-1) - partial2);
+			BUFFER_TRACE(partial2->bh, "call brelse");
+			brelse(partial2->bh);
+			partial2--;
 		}
-		brelse(bh);
-		bh = NULL;
+		goto do_indirects;
 	}
 
-err:
-	return ret;
-}
-
-int ext4_free_hole_blocks(handle_t *handle, struct inode *inode,
-			  ext4_lblk_t first, ext4_lblk_t stop)
-{
-	int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
-	int level, ret = 0;
-	int num = EXT4_NDIR_BLOCKS;
-	ext4_lblk_t count, max = EXT4_NDIR_BLOCKS;
-	__le32 *i_data = EXT4_I(inode)->i_data;
-
-	count = stop - first;
-	for (level = 0; level < 4; level++, max *= addr_per_block) {
-		if (first < max) {
-			ret = free_hole_blocks(handle, inode, NULL, i_data,
-					       level, first, count, num);
-			if (ret)
-				goto err;
-			if (count > max - first)
-				count -= max - first;
-			else
-				break;
-			first = 0;
-		} else {
-			first -= max;
+	/* Punch happened within the same level (n == n2) */
+	partial = ext4_find_shared(inode, n, offsets, chain, &nr);
+	partial2 = ext4_find_shared(inode, n2, offsets2, chain2, &nr2);
+	/*
+	 * ext4_find_shared returns Indirect structure which
+	 * points to the last element which should not be
+	 * removed by truncate. But this is end of the range
+	 * in punch_hole so we need to point to the next element
+	 */
+	partial2->p++;
+	while ((partial > chain) || (partial2 > chain2)) {
+		/* We're at the same block, so we're almost finished */
+		if ((partial->bh && partial2->bh) &&
+		    (partial->bh->b_blocknr == partial2->bh->b_blocknr)) {
+			if ((partial > chain) && (partial2 > chain2)) {
+				ext4_free_branches(handle, inode, partial->bh,
+						   partial->p + 1,
+						   partial2->p,
+						   (chain+n-1) - partial);
+				BUFFER_TRACE(partial->bh, "call brelse");
+				brelse(partial->bh);
+				BUFFER_TRACE(partial2->bh, "call brelse");
+				brelse(partial2->bh);
+			}
+			return 0;
 		}
-		i_data += num;
-		if (level == 0) {
-			num = 1;
-			max = 1;
+		/*
+		 * Clear the ends of indirect blocks on the shared branch
+		 * at the start of the range
+		 */
+		if (partial > chain) {
+			ext4_free_branches(handle, inode, partial->bh,
+				   partial->p + 1,
+				   (__le32 *)partial->bh->b_data+addr_per_block,
+				   (chain+n-1) - partial);
+			BUFFER_TRACE(partial->bh, "call brelse");
+			brelse(partial->bh);
+			partial--;
+		}
+		/*
+		 * Clear the ends of indirect blocks on the shared branch
+		 * at the end of the range
+		 */
+		if (partial2 > chain2) {
+			ext4_free_branches(handle, inode, partial2->bh,
+					   (__le32 *)partial2->bh->b_data,
+					   partial2->p,
+					   (chain2+n-1) - partial2);
+			BUFFER_TRACE(partial2->bh, "call brelse");
+			brelse(partial2->bh);
+			partial2--;
 		}
 	}
 
-err:
-	return ret;
+do_indirects:
+	/* Kill the remaining (whole) subtrees */
+	switch (offsets[0]) {
+	default:
+		if (++n >= n2)
+			return 0;
+		nr = i_data[EXT4_IND_BLOCK];
+		if (nr) {
+			ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 1);
+			i_data[EXT4_IND_BLOCK] = 0;
+		}
+	case EXT4_IND_BLOCK:
+		if (++n >= n2)
+			return 0;
+		nr = i_data[EXT4_DIND_BLOCK];
+		if (nr) {
+			ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 2);
+			i_data[EXT4_DIND_BLOCK] = 0;
+		}
+	case EXT4_DIND_BLOCK:
+		if (++n >= n2)
+			return 0;
+		nr = i_data[EXT4_TIND_BLOCK];
+		if (nr) {
+			ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 3);
+			i_data[EXT4_TIND_BLOCK] = 0;
+		}
+	case EXT4_TIND_BLOCK:
+		;
+	}
+	return 0;
 }
-

fs/ext4/inode.c

@@ -3506,7 +3506,7 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
 		ret = ext4_ext_remove_space(inode, first_block,
 					    stop_block - 1);
 	else
-		ret = ext4_free_hole_blocks(handle, inode, first_block,
+		ret = ext4_ind_remove_space(handle, inode, first_block,
 					    stop_block);
 
 	up_write(&EXT4_I(inode)->i_data_sem);