linux-ext4 - Re: DIO process stuck apparently due to dioread

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Date:	Tue, 16 Aug 2011 14:15:22 +0800
From:	Tao Ma <tm@....ma>
To:	Eric Sandeen <sandeen@...hat.com>
CC:	linux-ext4@...r.kernel.org, mjt@....msk.ru
Subject: Re: DIO process stuck apparently due to dioread_nolock (3.0)

Hi Eric,
On 08/16/2011 12:08 AM, Eric Sandeen wrote:
> On 8/13/11 11:02 AM, Tao Ma wrote:
>> From: Tao Ma <boyu.mt@...bao.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?
I have decided to leave it to the next merge window. So I will re-send
this patch as a fix and then create another patch for the helper
generalization.

Thanks
Tao
> 
> -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@...bao.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@....msk.ru>
>> Signed-off-by: Eric Sandeen <sandeen@...hat.com>
>> Signed-off-by: Tao Ma <boyu.mt@...bao.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));
> 
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