linux-ext4 - Re: [PATCH] ext4: queue conversion after adding to inode's completed IO list

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Message-ID: <4CAE022C.7050504@redhat.com>
Date:	Thu, 07 Oct 2010 12:23:56 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	ext4 development <linux-ext4@...r.kernel.org>
CC:	Jiaying Zhang <jiayingz@...gle.com>
Subject: Re: [PATCH] ext4: queue conversion after adding to inode's completed
 IO list

On 08/06/2010 02:52 PM, Eric Sandeen wrote:
> By queuing the io end on the unwritten workqueue before adding it
> to our inode's list of completed IOs, I think we run the risk
> of the work getting completed, and the IO freed, before we try
> to add it to the inode's i_completed_io_list.
> 
> It should be safe to add it to the inode's list of completed
> IOs, and -then- queue it for completion, I think.

Ping? would be good to fix this race, this has jiaying's ack too.

> Thanks to Dave Chinner for pointing out the race.
> 
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
> ---
> 
> (At least I think this is right; I haven't actually demonstrated a race...)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 0afc8c1..7f56c48 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3804,14 +3804,14 @@ static void ext4_end_io_dio(struct kiocb *iocb, loff_t offset,
>  	io_end->flag = EXT4_IO_UNWRITTEN;
>  	wq = EXT4_SB(io_end->inode->i_sb)->dio_unwritten_wq;
>  
> -	/* queue the work to convert unwritten extents to written */
> -	queue_work(wq, &io_end->work);
> -
>  	/* Add the io_end to per-inode completed aio dio list*/
>  	ei = EXT4_I(io_end->inode);
>  	spin_lock_irqsave(&ei->i_completed_io_lock, flags);
>  	list_add_tail(&io_end->list, &ei->i_completed_io_list);
>  	spin_unlock_irqrestore(&ei->i_completed_io_lock, flags);
> +
> +	/* queue the work to convert unwritten extents to written */
> +	queue_work(wq, &io_end->work);
>  	iocb->private = NULL;
>  out:
>  	if (is_async)
> 
> --
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