linux-ext4 - Re: [PATCH] ext4: use directio end_io error status to finish unwritten aio dio correctly

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Date:	Fri, 19 Feb 2016 09:02:32 +1100
From:	Dave Chinner <david@...morbit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	"Darrick J. Wong" <darrick.wong@...cle.com>,
	Theodore Ts'o <tytso@....edu>,
	linux-ext4 <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: use directio end_io error status to finish
 unwritten aio dio correctly

On Wed, Feb 17, 2016 at 10:01:48PM -0800, Christoph Hellwig wrote:
> Might help to tell that this is on top of a direct-io.c patch from the
> XFS tree.
> 
> I don't think clearing any flags is the right thing - now that we
> always call ->end_io the code dealing with it in ext4_ext_direct_IO
> can simply be moved to the ->end_io handler.
> 
> Something like the untested patch below:
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 9db04dd..b741c79 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3166,23 +3166,25 @@ static int ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
>  {
>          ext4_io_end_t *io_end = iocb->private;
>  
> -	if (size <= 0)
> -		return 0;
> -
>  	/* if not async direct IO just return */
>  	if (!io_end)
>  		return 0;
>  
> +	if (size <= 0) {
> +		WARN_ON(io_end->flag & EXT4_IO_END_UNWRITTEN);
> +		goto out;
> +	}

That will still issue a warning when an I/O error occurs on an
unwritten extent.

> +
>  	ext_debug("ext4_end_io_dio(): io_end 0x%p "
>  		  "for inode %lu, iocb 0x%p, offset %llu, size %zd\n",
>   		  iocb->private, io_end->inode->i_ino, iocb, offset,
>  		  size);
>  
> -	iocb->private = NULL;
>  	io_end->offset = offset;
>  	io_end->size = size;
> +out:
>  	ext4_put_io_end(io_end);

Won't that now call ext4_put_io_end() ->
ext4_convert_unwritten_extents() with an uninitialised offset and
size?

i.e. I don't think this prevents warnings, and may make things
worse when real errors occur....

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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