Commit c278531d authored by Dmitry Monakhov's avatar Dmitry Monakhov Committed by Theodore Ts'o
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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: default avatarDmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
parent 041bbb6d

fs/ext4/ext4.h

+2 −1
Original line number Diff line number Diff line
@@ -1947,7 +1947,7 @@ extern void ext4_htree_free_dir_info(struct dir_private_info *p); 


/* fsync.c */

extern int ext4_sync_file(struct file *, loff_t, loff_t, int);

extern int ext4_flush_completed_IO(struct inode *);

extern int ext4_flush_unwritten_io(struct inode *);



/* hash.c */

extern int ext4fs_dirhash(const char *name, int len, struct
@@ -2371,6 +2371,7 @@ extern const struct file_operations ext4_dir_operations; 
extern const struct inode_operations ext4_file_inode_operations;

extern const struct file_operations ext4_file_operations;

extern loff_t ext4_llseek(struct file *file, loff_t offset, int origin);

extern void ext4_unwritten_wait(struct inode *inode);



/* namei.c */

extern const struct inode_operations ext4_dir_inode_operations;

fs/ext4/extents.c

+3 −3
Original line number Diff line number Diff line
@@ -4268,7 +4268,7 @@ void ext4_ext_truncate(struct inode *inode) 
	 * 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 @@ int ext4_ext_punch_hole(struct file *file, loff_t offset, loff_t length) 


	/* 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);

fs/ext4/file.c

+1 −1
Original line number Diff line number Diff line
@@ -55,7 +55,7 @@ static int ext4_release_file(struct inode *inode, struct file *filp) 
	return 0;

}



static void ext4_unwritten_wait(struct inode *inode)

void ext4_unwritten_wait(struct inode *inode)

{

	wait_queue_head_t *wq = ext4_ioend_wq(inode);

fs/ext4/fsync.c

+1 −1
Original line number Diff line number Diff line
@@ -138,7 +138,7 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync) 
	if (inode->i_sb->s_flags & MS_RDONLY)

		goto out;



	ret = ext4_flush_completed_IO(inode);

	ret = ext4_flush_unwritten_io(inode);

	if (ret < 0)

		goto out;

fs/ext4/indirect.c

+5 −3
Original line number Diff line number Diff line
@@ -807,9 +807,11 @@ ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb, 


retry:

	if (rw == READ && ext4_should_dioread_nolock(inode)) {

		if (unlikely(!list_empty(&ei->i_completed_io_list)))

			ext4_flush_completed_IO(inode);



		if (unlikely(atomic_read(&EXT4_I(inode)->i_unwritten))) {

			mutex_lock(&inode->i_mutex);

			ext4_flush_unwritten_io(inode);

			mutex_unlock(&inode->i_mutex);

		}

		/*

		 * Nolock dioread optimization may be dynamically disabled

		 * via ext4_inode_block_unlocked_dio(). Check inode's state

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