Re: DIO process stuck apparently due to dioread_nolock (3.0)

[Eric Sandeen <sandeen@redhat.com>]

On 8/13/11 11:02 AM, Tao Ma wrote:
> From: Tao Ma <boyu.mt@taobao.com>
> 
> Hi Michael,
> 	could you please check whether this patch work for you?

Thanks, this is the patch I meant to send, I guess ;)  I think
I missed the "|=" case before :(

given that every place we set it requires a test and an increment
if not set, maybe a helper to do all that is in order?

-Eric

> 
> Subject: [PATCH] ext4: Set unwritten flag and increase i_aiodio_unwritten simultaneously.
> From 4f1d797973da8b5cf79f58cc1e4d22efb9d46d19 Mon Sep 17 00:00:00 2001
> From: Tao Ma <boyu.mt@taobao.com>
> Date: Sat, 13 Aug 2011 23:50:28 +0800
> Subject: [PATCH] ext4: Set unwritten flag and increase i_aiodio_unwritten simultaneously.
> 
> 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.
> http://marc.info/?l=linux-ext4&m=131316851417460&w=2
> 
> Reported-by: Michael Tokarev<mjt@tls.msk.ru>
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> Signed-off-by: Tao Ma <boyu.mt@taobao.com>
> ---
>  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));