[PATCH 3.16 017/245] ext4: fix races of writeback with punch hole and zero range

Ben Hutchings
2020-04-23T23:06:50Z

From: Jan Kara <jack@suse.com>

commit 011278485ecc3cd2a3954b5d4c73101d919bf1fa upstream.

When doing delayed allocation, update of on-disk inode size is postponed
until IO submission time. However hole punch or zero range fallocate
calls can end up discarding the tail page cache page and thus on-disk
inode size would never be properly updated.

Make sure the on-disk inode size is updated before truncating page
cache.

Signed-off-by: Jan Kara <jack@suse.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/ext4/ext4.h | 3 +++
fs/ext4/extents.c | 5 +++++
fs/ext4/inode.c | 35 ++++++++++++++++++++++++++++++++++-
3 files changed, 42 insertions(+), 1 deletion(-)

--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -2560,6 +2560,9 @@ static inline int ext4_update_inode_size
return changed;
}

+int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
+ loff_t len);
+
struct ext4_group_info {
unsigned long bb_state;
struct rb_root bb_free_root;
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4856,6 +4856,11 @@ static long ext4_zero_range(struct file
* released from page cache.
*/
down_write(&EXT4_I(inode)->i_mmap_sem);
+ ret = ext4_update_disksize_before_punch(inode, offset, len);
+ if (ret) {
+ up_write(&EXT4_I(inode)->i_mmap_sem);
+ goto out_dio;
+ }
/* Now release the pages and zero block aligned part of pages */
truncate_pagecache_range(inode, start, end - 1);
inode->i_mtime = inode->i_ctime = ext4_current_time(inode);
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3652,6 +3652,35 @@ int ext4_can_truncate(struct inode *inod
}

/*
+ * We have to make sure i_disksize gets properly updated before we truncate
+ * page cache due to hole punching or zero range. Otherwise i_disksize update
+ * can get lost as it may have been postponed to submission of writeback but
+ * that will never happen after we truncate page cache.
+ */
+int ext4_update_disksize_before_punch(struct inode *inode, loff_t offset,
+ loff_t len)
+{
+ handle_t *handle;
+ loff_t size = i_size_read(inode);
+
+ WARN_ON(!mutex_is_locked(&inode->i_mutex));
+ if (offset > size || offset + len < size)
+ return 0;
+
+ if (EXT4_I(inode)->i_disksize >= size)
+ return 0;
+
+ handle = ext4_journal_start(inode, EXT4_HT_MISC, 1);
+ if (IS_ERR(handle))
+ return PTR_ERR(handle);
+ ext4_update_i_disksize(inode, size);
+ ext4_mark_inode_dirty(handle, inode);
+ ext4_journal_stop(handle);
+
+ return 0;
+}
+
+/*
* ext4_punch_hole: punches a hole in a file by releaseing the blocks
* associated with the given offset and length
*
@@ -3729,9 +3758,13 @@ int ext4_punch_hole(struct inode *inode,
last_block_offset = round_down((offset + length), sb->s_blocksize) - 1;

/* Now release the pages and zero block aligned part of pages*/
- if (last_block_offset > first_block_offset)
+ if (last_block_offset > first_block_offset) {
+ ret = ext4_update_disksize_before_punch(inode, offset, length);
+ if (ret)
+ goto out_dio;
truncate_pagecache_range(inode, first_block_offset,
last_block_offset);
+ }

if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
credits = ext4_writepage_trans_blocks(inode);