linux-ext4 - Re: [PATCH 5/7] ext4: serialize unlocked dio reads with truncate

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Date:	Mon, 10 Sep 2012 11:54:50 +0200
From:	Jan Kara <jack@...e.cz>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz,
	wenqing.lz@...bao.com
Subject: Re: [PATCH 5/7] ext4: serialize unlocked dio reads with truncate

On Sun 09-09-12 21:27:12, Dmitry Monakhov wrote:
> Current serialization will works only for DIO which holds
> i_mutex, but nonlocked DIO following race is possible:
> 
> dio_nolock_read_task            truncate_task
> 				->ext4_setattr()
> 				 ->inode_dio_wait()
> ->ext4_ext_direct_IO
>   ->ext4_ind_direct_IO
>     ->__blockdev_direct_IO
>       ->ext4_get_block
> 				 ->truncate_setsize()
> 				 ->ext4_truncate()
> 				 #alloc truncated blocks
> 				 #to other inode
>       ->submit_io()
>      #INFORMATION LEAK
> 
> In order to serialize with unlocked DIO reads we have to
> rearrange wait sequence
> 1) update i_size first
> 2) if i_size about to be reduced wait for outstanding DIO requests
> 3) and only after that truncate inode blocks
  Looks good. You can add:
Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
> 
> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
> ---
>  fs/ext4/inode.c |    7 +++++--
>  1 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index ffb4a27..93e6b09 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -4283,7 +4283,6 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
>  	}
>  
>  	if (attr->ia_valid & ATTR_SIZE) {
> -		inode_dio_wait(inode);
>  
>  		if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
>  			struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);
> @@ -4332,8 +4331,12 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
>  	}
>  
>  	if (attr->ia_valid & ATTR_SIZE) {
> -		if (attr->ia_size != i_size_read(inode))
> +		if (attr->ia_size != inode->i_size) {
>  			truncate_setsize(inode, attr->ia_size);
> +			/* Inode size will be reduced, wait for dio in flight */
> +			if (orphan)
> +				inode_dio_wait(inode);
> +		}
>  		ext4_truncate(inode);
>  	}
>  
> -- 
> 1.7.7.6
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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