Re: [PATCH] ext4: Create helper function for EXT4_IO_END_UNWRITTEN and i_aiodio_unwritten.

[Tao Ma <tm@tao.ma>]

On 08/16/2011 10:04 PM, Eric Sandeen wrote:
> On 8/16/11 2:06 AM, Tao Ma wrote:
>> From: Tao Ma <boyu.mt@taobao.com>
>>
>> EXT4_IO_END_UNWRITTEN flag set and the increase of i_aiodio_unwritten should
>> be done simultaneously since ext4_end_io_nolock always clear the flag and
>> decrease the counter in the same time.
>>
>> We have found some bugs that the flag is set while leaving i_aiodio_unwritten
>> unchanged. So this patch just tries to creat a helper function to wrap them
>> to avoid any future bug. The idea is inspired by Eric.
> 
> Although I like it a little less now that I see it in practice, sorry.   ;)
> 
> This:
>                 /*
>                  * Flag the inode(non aio case) or end_io struct (aio case)
>                  * that this IO needs to conversion to written when IO is
>                  * completed
>                  */
> 		if (!ext4_set_io_unwritten_flag(inode, io))
> 			ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
> 
> just reads weirdly to me.
yeah, this also looks a little bit strange. Another possible way is that
we just wrap the set of the flag and the inc of aiodio_unwritten while
leave the check there. It should look more natural and good for the reader.
> 
> It encapsulates all the steps, but it really isn't intuitive to read, I think.
> 
> "If we (can't? don't?) set the io unwritten flag, set the dio unwritten flag
> on the inode."
> 
> I wonder if changing "io" to "endio" would make it a little more obvious.
> 
> I'm not sure, maybe it's ok.  What do others think?
> 
> I also wonder about this, but I get lost in this code.  It was originally:
> 
>                 if (io && !(io->flag & EXT4_IO_END_UNWRITTEN)) {
>                         io->flag = EXT4_IO_END_UNWRITTEN;
>                         atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
>                 } else
>                         ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
> 
> That means that if it is AIO ("if (io)"), but the flag is already set
> (io->flag & EXT4_IO_END_UNWRITTEN), we don't re-set the flag or increase
> the count, which is fine - but is it then correct to set the state on the
> inode?
I will check it later.

Thanks
Tao
> 
> thanks,
> -Eric
> 
>> Cc: Eric Sandeen <sandeen@redhat.com>
>> Cc: "Theodore Ts'o" <tytso@mit.edu>
>> Signed-off-by: Tao Ma <boyu.mt@taobao.com>
>> ---
>> Ted,
>> 	This patch is based on the patch with subject "ext4: Resolve the hang
>> of direct i/o read in handling EXT4_IO_END_UNWRITTEN.". I meant it for the next
>> merge window, but if you think it is also ok for 3.1, go ahead.
>>
>>  fs/ext4/ext4.h    |   11 +++++++++++
>>  fs/ext4/extents.c |   10 ++--------
>>  fs/ext4/inode.c   |    5 +----
>>  fs/ext4/page-io.c |    6 ++----
>>  4 files changed, 16 insertions(+), 16 deletions(-)
>>
>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>> index e717dfd..514f670 100644
>> --- a/fs/ext4/ext4.h
>> +++ b/fs/ext4/ext4.h
>> @@ -1247,6 +1247,17 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
>>  		 ino <= le32_to_cpu(EXT4_SB(sb)->s_es->s_inodes_count));
>>  }
>>  
>> +static inline int ext4_set_io_unwritten_flag(struct inode *inode,
>> +					     struct ext4_io_end *io_end)
>> +{
>> +	if (io_end && !(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
>> +		io_end->flag |= EXT4_IO_END_UNWRITTEN;
>> +		atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
>> +		return 1;
>> +	}
>> +
>> +	return 0;
>> +}
>>  /*
>>   * Inode dynamic state flags
>>   */
>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>> index 57cf568..c0f8655 100644
>> --- a/fs/ext4/extents.c
>> +++ b/fs/ext4/extents.c
>> @@ -3190,10 +3190,7 @@ ext4_ext_handle_uninitialized_extents(handle_t *handle, struct inode *inode,
>>  		 * that this IO needs to conversion to written when IO is
>>  		 * completed
>>  		 */
>> -		if (io && !(io->flag & EXT4_IO_END_UNWRITTEN)) {
>> -			io->flag = EXT4_IO_END_UNWRITTEN;
>> -			atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
>> -		} else
>> +		if (!ext4_set_io_unwritten_flag(inode, io))
>>  			ext4_set_inode_state(inode, EXT4_STATE_DIO_UNWRITTEN);
>>  		if (ext4_should_dioread_nolock(inode))
>>  			map->m_flags |= EXT4_MAP_UNINIT;
>> @@ -3572,10 +3569,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
>>  		 * that we need to perform conversion when IO is done.
>>  		 */
>>  		if ((flags & EXT4_GET_BLOCKS_PRE_IO)) {
>> -			if (io && !(io->flag & EXT4_IO_END_UNWRITTEN)) {
>> -				io->flag = EXT4_IO_END_UNWRITTEN;
>> -				atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
>> -			} else
>> +			if (!ext4_set_io_unwritten_flag(inode, io))
>>  				ext4_set_inode_state(inode,
>>  						     EXT4_STATE_DIO_UNWRITTEN);
>>  		}
>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>> index 40c0b10..128493b 100644
>> --- a/fs/ext4/inode.c
>> +++ b/fs/ext4/inode.c
>> @@ -2673,10 +2673,7 @@ static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
>>  	 * but being more careful is always safe for the future change.
>>  	 */
>>  	inode = io_end->inode;
>> -	if (!(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
>> -		io_end->flag |= EXT4_IO_END_UNWRITTEN;
>> -		atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
>> -	}
>> +	ext4_set_io_unwritten_flag(inode, io_end);
>>  
>>  	/* Add the io_end to per-inode completed io list*/
>>  	spin_lock_irqsave(&EXT4_I(inode)->i_completed_io_lock, flags);
>> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
>> index 78839af..edd2f7b 100644
>> --- a/fs/ext4/page-io.c
>> +++ b/fs/ext4/page-io.c
>> @@ -334,10 +334,8 @@ submit_and_retry:
>>  	if ((io_end->num_io_pages >= MAX_IO_PAGES) &&
>>  	    (io_end->pages[io_end->num_io_pages-1] != io_page))
>>  		goto submit_and_retry;
>> -	if (buffer_uninit(bh) && !(io_end->flag & EXT4_IO_END_UNWRITTEN)) {
>> -		io_end->flag |= EXT4_IO_END_UNWRITTEN;
>> -		atomic_inc(&EXT4_I(inode)->i_aiodio_unwritten);
>> -	}
>> +	if (buffer_uninit(bh))
>> +		ext4_set_io_unwritten_flag(inode, io_end);
>>  	io->io_end->size += bh->b_size;
>>  	io->io_next_block++;
>>  	ret = bio_add_page(io->io_bio, bh->b_page, bh->b_size, bh_offset(bh));
>