linux-ext4 - Re: [PATCH] ext4: Resolve the hang of direct i/o read in handling EXT4_IO_END

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Message-ID: <4E4A7954.8030603@redhat.com>
Date:	Tue, 16 Aug 2011 09:06:12 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Tao Ma <tm@....ma>
CC:	linux-ext4@...r.kernel.org, mjt@....msk.ru, tytso@....edu
Subject: Re: [PATCH] ext4: Resolve the hang of direct i/o read in handling
 EXT4_IO_END_UNWRITTEN.

On 8/16/11 1:37 AM, Tao Ma wrote:
> From: Tao Ma <boyu.mt@...bao.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 don't increase i_aiodio_unwritten when setting EXT4_IO_END_UNWRITTEN so
> it will go nagative and causes some process to wait forever.
> 
> Part of the patch came from Eric in his e-mail, but it doesn't fix the problem
> met by Michael actually.
> http://marc.info/?l=linux-ext4&m=131316851417460&w=2
> 
> Reported-and-Tested-by: Michael Tokarev<mjt@....msk.ru>
> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
> Signed-off-by: Tao Ma <boyu.mt@...bao.com>

Yes, this looks right to me.  It's the patch I meant to send, but
I missed one spot in my haste.  ;)  Thanks.

-Eric

> ---
> Eric talked about creating a helper for this and I feel that it looks
> like a new functionality not a bug fix and decided to leave it to the
> next merge window.
> 
>  fs/ext4/inode.c   |    9 ++++++++-
>  fs/ext4/page-io.c |    6 ++++--
>  2 files changed, 12 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index d47264c..40c0b10 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -2668,8 +2668,15 @@ static void ext4_end_io_buffer_write(struct buffer_head *bh, int uptodate)
>  		goto out;
>  	}
>  
> -	io_end->flag = EXT4_IO_END_UNWRITTEN;
> +	/*
> +	 * It may be over-defensive here to check EXT4_IO_END_UNWRITTEN now,
> +	 * 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);
> +	}
>  
>  	/* 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 430c401..78839af 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -334,8 +334,10 @@ 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->io_end->flag |= EXT4_IO_END_UNWRITTEN;
> +	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);
> +	}
>  	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));

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