linux-ext4 - Re: [PATCH]ext4: Add checks whether two inodes are different

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Date:	Fri, 25 Sep 2009 04:34:53 -0600
From:	Andreas Dilger <adilger@....com>
To:	Akira Fujita <a-fujita@...jp.nec.com>
Cc:	Theodore Tso <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH]ext4: Add checks whether two inodes are different

On Sep 25, 2009  17:31 +0900, Akira Fujita wrote:
> ext4: Add checks whether two inodes are different to move_extent.c
> 
> From: Akira Fujita <a-fujita@...jp.nec.com>
> 
> If same inode is set to orig and donor in ext4_move_extensts(),
> this leads to the deadlock in mext_double_down_{read, write}.
> This patch adds checks to mext_double_{down, up}_{read, write}
> and if inodes are same, we take/release one semaphore from them.

Wouldn't it make more sense to just return an error (or no error
but do nothing) in the case of source/target inode being the same?
I don't see how that would be good to "defragment" the inode onto
itself, just like "cp f f" and "rename f f" don't make sense either.

> Signed-off-by: Akira Fujita <a-fujita@...jp.nec.com>
> ---
>  fs/ext4/move_extent.c |   14 +++++++++-----
>  1 files changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
> index c07a291..e1346cb 100644
> --- a/fs/ext4/move_extent.c
> +++ b/fs/ext4/move_extent.c
> @@ -177,7 +177,8 @@ mext_double_down_read(struct inode *orig_inode, struct inode *donor_inode)
>  	}
> 
>  	down_read(&EXT4_I(first)->i_data_sem);
> -	down_read(&EXT4_I(second)->i_data_sem);
> +	if (first != second)
> +		down_read(&EXT4_I(second)->i_data_sem);
>  }
> 
>  /**
> @@ -203,7 +204,8 @@ mext_double_down_write(struct inode *orig_inode, struct inode *donor_inode)
>  	}
> 
>  	down_write(&EXT4_I(first)->i_data_sem);
> -	down_write(&EXT4_I(second)->i_data_sem);
> +	if (first != second)
> +		down_write(&EXT4_I(second)->i_data_sem);
>  }
> 
>  /**
> @@ -217,7 +219,8 @@ static void
>  mext_double_up_read(struct inode *orig_inode, struct inode *donor_inode)
>  {
>  	up_read(&EXT4_I(orig_inode)->i_data_sem);
> -	up_read(&EXT4_I(donor_inode)->i_data_sem);
> +	if (orig_inode != donor_inode)
> +		up_read(&EXT4_I(donor_inode)->i_data_sem);
>  }
> 
>  /**
> @@ -231,7 +234,8 @@ static void
>  mext_double_up_write(struct inode *orig_inode, struct inode *donor_inode)
>  {
>  	up_write(&EXT4_I(orig_inode)->i_data_sem);
> -	up_write(&EXT4_I(donor_inode)->i_data_sem);
> +	if (orig_inode != donor_inode)
> +		up_write(&EXT4_I(donor_inode)->i_data_sem);
>  }
> 
>  /**
> @@ -1002,7 +1006,7 @@ mext_check_arguments(struct inode *orig_inode,
>  	}
> 
>  	/* orig and donor should be different file */
> -	if (orig_inode->i_ino == donor_inode->i_ino) {
> +	if (orig_inode == donor_inode) {
>  		ext4_debug("ext4 move extent: The argument files should not "
>  			"be same file [ino:orig %lu, donor %lu]\n",
>  			orig_inode->i_ino, donor_inode->i_ino);
> 
> --
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Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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