Commit 4c546592 authored Apr 25, 2016 by Daeho Jeong Committed by Theodore Ts'o Apr 25, 2016

ext4: handle unwritten or delalloc buffers before enabling data journaling



We already allocate delalloc blocks before changing the inode mode into
"per-file data journal" mode to prevent delalloc blocks from remaining
not allocated, but another issue concerned with "BH_Unwritten" status
still exists. For example, by fallocate(), several buffers' status
change into "BH_Unwritten", but these buffers cannot be processed by
ext4_alloc_da_blocks(). So, they still remain in unwritten status after
per-file data journaling is enabled and they cannot be changed into
written status any more and, if they are journaled and eventually
checkpointed, these unwritten buffer will cause a kernel panic by the
below BUG_ON() function of submit_bh_wbc() when they are submitted
during checkpointing.

static int submit_bh_wbc(int rw, struct buffer_head *bh,...
{
        ...
        BUG_ON(buffer_unwritten(bh));

Moreover, when "dioread_nolock" option is enabled, the status of a
buffer is changed into "BH_Unwritten" after write_begin() completes and
the "BH_Unwritten" status will be cleared after I/O is done. Therefore,
if a buffer's status is changed into unwrutten but the buffer's I/O is
not submitted and completed, it can cause the same problem after
enabling per-file data journaling. You can easily generate this bug by
executing the following command.

./kvm-xfstests -C 10000 -m nodelalloc,dioread_nolock generic/269

To resolve these problems and define a boundary between the previous
mode and per-file data journaling mode, we need to flush and wait all
the I/O of buffers of a file before enabling per-file data journaling
of the file.

Signed-off-by: Daeho Jeong <daeho.jeong@samsung.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

parent 7b808191

fs/ext4/inode.c

+20 −11

Original line number	Diff line number	Diff line
		@@ -5452,22 +5452,29 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
		return 0;
		if (is_journal_aborted(journal))
		return -EROFS;
		/* We have to allocate physical blocks for delalloc blocks
		* before flushing journal. otherwise delalloc blocks can not
		* be allocated any more. even more truncate on delalloc blocks
		* could trigger BUG by flushing delalloc blocks in journal.
		* There is no delalloc block in non-journal data mode.
		*/
		if (val && test_opt(inode->i_sb, DELALLOC)) {
		err = ext4_alloc_da_blocks(inode);
		if (err < 0)
		return err;
		}

		/* Wait for all existing dio workers */
		ext4_inode_block_unlocked_dio(inode);
		inode_dio_wait(inode);

		/*
		* Before flushing the journal and switching inode's aops, we have
		* to flush all dirty data the inode has. There can be outstanding
		* delayed allocations, there can be unwritten extents created by
		* fallocate or buffered writes in dioread_nolock mode covered by
		* dirty data which can be converted only after flushing the dirty
		* data (and journalled aops don't know how to handle these cases).
		*/
		if (val) {
		down_write(&EXT4_I(inode)->i_mmap_sem);
		err = filemap_write_and_wait(inode->i_mapping);
		if (err < 0) {
		up_write(&EXT4_I(inode)->i_mmap_sem);
		ext4_inode_resume_unlocked_dio(inode);
		return err;
		}
		}

		jbd2_journal_lock_updates(journal);

		/*
		@@ -5492,6 +5499,8 @@ int ext4_change_inode_journal_flag(struct inode *inode, int val)
		ext4_set_aops(inode);

		jbd2_journal_unlock_updates(journal);
		if (val)
		up_write(&EXT4_I(inode)->i_mmap_sem);
		ext4_inode_resume_unlocked_dio(inode);

		/* Finally we can mark the inode as dirty. */