[PATCH 3.13 077/187] ext4: fix punch hole on files with indirect mapping

Kamal Mostafa
2014-09-15T22:17:10Z

From: Lukas Czerner <lczerner@redhat.com>

commit 4f579ae7de560e5f449587a6c3f02594d53d4d51 upstream.

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.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
fs/ext4/ext4.h | 4 +-
fs/ext4/indirect.c | 281 ++++++++++++++++++++++++++++++++++++++---------------
fs/ext4/inode.c | 2 +-
3 files changed, 205 insertions(+), 82 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 62f024c..e531054 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2151,8 +2151,8 @@ 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);
diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
index c30cbe2..4353522 100644
--- a/fs/ext4/indirect.c
+++ b/fs/ext4/indirect.c
@@ -1297,97 +1297,220 @@ do_indirects:
}
}

-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;
}
-
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 0fc189b..23e8c80 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3629,7 +3629,7 @@ 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);

ext4_discard_preallocations(inode);
--
1.9.1