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

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Date:	Fri, 6 Aug 2010 13:45:10 -0700
From:	Jiaying Zhang <jiayingz@...gle.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH] ext4: queue conversion after adding to inode's completed 
	IO list

Lgtm. Thanks for the fixing patch.

Jiaying

On Fri, Aug 6, 2010 at 12:52 PM, Eric Sandeen <sandeen@...hat.com> 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.
>
> 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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