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>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 17bfa42ac97132dff751baace2e73c4c9de3d120..779ef4c11bc17c66620aa2f5facd86a15779409a 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -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. */