ext4: fix ext4_flush_completed_IO wait semantics
BUG #1) All places where we call ext4_flush_completed_IO are broken
because buffered io and DIO/AIO goes through three stages
1) submitted io,
2) completed io (in i_completed_io_list) conversion pended
3) finished io (conversion done)
And by calling ext4_flush_completed_IO we will flush only
requests which were in (2) stage, which is wrong because:
1) punch_hole and truncate _must_ wait for all outstanding unwritten io
regardless to it's state.
2) fsync and nolock_dio_read should also wait because there is
a time window between end_page_writeback() and ext4_add_complete_io()
As result integrity fsync is broken in case of buffered write
to fallocated region:
fsync blkdev_completion
->filemap_write_and_wait_range
->ext4_end_bio
->end_page_writeback
<-- filemap_write_and_wait_range return
->ext4_flush_completed_IO
sees empty i_completed_io_list but pended
conversion still exist
->ext4_add_complete_io
BUG #2) Race window becomes wider due to the 'ext4: completed_io
locking cleanup V4' patch series
This patch make following changes:
1) ext4_flush_completed_io() now first try to flush completed io and when
wait for any outstanding unwritten io via ext4_unwritten_wait()
2) Rename function to more appropriate name.
3) Assert that all callers of ext4_flush_unwritten_io should hold i_mutex to
prevent endless wait
Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index c1fcf48..1c94cca 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4268,7 +4268,7 @@
* finish any pending end_io work so we won't run the risk of
* converting any truncated blocks to initialized later
*/
- ext4_flush_completed_IO(inode);
+ ext4_flush_unwritten_io(inode);
/*
* probably first extent we're gonna free will be last in block
@@ -4847,10 +4847,10 @@
/* Wait all existing dio workers, newcomers will block on i_mutex */
ext4_inode_block_unlocked_dio(inode);
- inode_dio_wait(inode);
- err = ext4_flush_completed_IO(inode);
+ err = ext4_flush_unwritten_io(inode);
if (err)
goto out_dio;
+ inode_dio_wait(inode);
credits = ext4_writepage_trans_blocks(inode);
handle = ext4_journal_start(inode, credits);