Commit 51e3ae81 authored Oct 06, 2017 by Theodore Ts'o

ext4: fix interaction between i_size, fallocate, and delalloc after a crash



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>
Cc: stable@vger.kernel.org

parent 68fd9750

fs/ext4/extents.c

+4 −2

Original line number	Diff line number	Diff line
		@@ -4794,7 +4794,8 @@ static long ext4_zero_range(struct file *file, loff_t offset,
		}

		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)
		@@ -4965,7 +4966,8 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
		}

		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)

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