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ext4: fix ext4_flush_completed_IO wait semantics

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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>
This commit is contained in:
Dmitry Monakhov 2012-10-05 11:31:55 -04:00 committed by Theodore Ts'o
parent 041bbb6d36
commit c278531d39
6 changed files with 19 additions and 13 deletions
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3
fs/ext4/ext4.h
View File

@ -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;

6
fs/ext4/extents.c
View File

@ -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);

2
fs/ext4/file.c
View File

@ -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);

2
fs/ext4/fsync.c
View File

@ -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;

8
fs/ext4/indirect.c
View File

@ -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

11
fs/ext4/page-io.c
View File

@ -189,8 +189,6 @@ static int ext4_do_flush_completed_IO(struct inode *inode,
list_add_tail(&io->list, &complete);
}
/* It is important to update all flags for all end_io in one shot w/o
* dropping the lock.*/
spin_lock_irqsave(&ei->i_completed_io_lock, flags);
while (!list_empty(&complete)) {
io = list_entry(complete.next, ext4_io_end_t, list);
@ -228,9 +226,14 @@ static void ext4_end_io_work(struct work_struct *work)
ext4_do_flush_completed_IO(io->inode, io);
}
int ext4_flush_completed_IO(struct inode *inode)
int ext4_flush_unwritten_io(struct inode *inode)
{
return ext4_do_flush_completed_IO(inode, NULL);
int ret;
WARN_ON_ONCE(!mutex_is_locked(&inode->i_mutex) &&
!(inode->i_state & I_FREEING));
ret = ext4_do_flush_completed_IO(inode, NULL);
ext4_unwritten_wait(inode);
return ret;
}
ext4_io_end_t *ext4_init_io_end(struct inode *inode, gfp_t flags)