[PATCH 4.4 31/96] ext4: fix interaction between i_size, fallocate, and delalloc after a crash

Greg Kroah-Hartman
2017-11-28T10:22:40Z

From: Theodore Ts'o <tytso@mit.edu>

commit 51e3ae81ec58e95f10a98ef3dd6d7bce5d8e35a2 upstream.

If there are pending writes subject to delayed allocation, then i_size
will show size after the writes have completed, while i_disksize
contains the value of i_size on the disk (since the writes have not
been persisted to disk).

If fallocate(2) is called with the FALLOC_FL_KEEP_SIZE flag, either
with or without the FALLOC_FL_ZERO_RANGE flag set, and the new size
after the fallocate(2) is between i_size and i_disksize, then after a
crash, if a journal commit has resulted in the changes made by the
fallocate() call to be persisted after a crash, but the delayed
allocation write has not resolved itself, i_size would not be updated,
and this would cause the following e2fsck complaint:

Inode 12, end of extent exceeds allowed value
(logical block 33, physical block 33441, len 7)

This can only take place on a sparse file, where the fallocate(2) call
is allocating blocks in a range which is before a pending delayed
allocation write which is extending i_size. Since this situation is
quite rare, and the window in which the crash must take place is
typically < 30 seconds, in practice this condition will rarely happen.

Nevertheless, it can be triggered in testing, and in particular by
xfstests generic/456.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reported-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/ext4/extents.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4818,7 +4818,8 @@ static long ext4_zero_range(struct file
}

if (!(mode & FALLOC_FL_KEEP_SIZE) &&
- offset + len > i_size_read(inode)) {
+ (offset + len > i_size_read(inode) ||
+ offset + len > EXT4_I(inode)->i_disksize)) {
new_size = offset + len;
ret = inode_newsize_ok(inode, new_size);
if (ret)
@@ -4994,7 +4995,8 @@ long ext4_fallocate(struct file *file, i
}

if (!(mode & FALLOC_FL_KEEP_SIZE) &&
- offset + len > i_size_read(inode)) {
+ (offset + len > i_size_read(inode) ||
+ offset + len > EXT4_I(inode)->i_disksize)) {
new_size = offset + len;
ret = inode_newsize_ok(inode, new_size);
if (ret)