linux-kernel - Re: [PATCH 1/2] LSEEK: BTRFS: Avoid i_mutex for SEEK

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Date:	Wed, 2 Nov 2011 04:29:15 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Andres Freund <andres@...razel.de>
Cc:	Andi Kleen <andi@...stfloor.org>, robertmhaas@...il.com,
	viro@...iv.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, chris.mason@...cle.com,
	linux-btrfs@...r.kernel.org
Subject: Re: [PATCH 1/2] LSEEK: BTRFS: Avoid i_mutex for SEEK_{CUR,SET,END}

Andres, can you check with Chris that the btrfs changes made it to
his tree?  The core lseek changes from Andi are in mainline now, but
I think these bits are better off going through Chrises btrfs tree.

On Sat, Oct 01, 2011 at 10:49:27PM +0200, Andres Freund wrote:
> 
> Don't need the i_mutex for those cases, only for SEEK_HOLE/DATA.
> 
> Really-From: Andi Kleen <ak@...ux.intel.com>
> Signed-off-by: Andi Kleen <ak@...ux.intel.com>
> Signed-off-by: Andres Freund <andres@...razel.de>
> ---
>  fs/btrfs/file.c |   27 +++++++++++----------------
>  1 files changed, 11 insertions(+), 16 deletions(-)
> 
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 7a13337..5bc7116 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1809,24 +1809,19 @@ static loff_t btrfs_file_llseek(struct file *file, loff_t offset, int origin)
>  	struct inode *inode = file->f_mapping->host;
>  	int ret;
>  
> +	if (origin != SEEK_DATA && origin != SEEK_HOLE)
> +		return generic_file_llseek(file, offset, origin);
> +
>  	mutex_lock(&inode->i_mutex);
> -	switch (origin) {
> -	case SEEK_END:
> -	case SEEK_CUR:
> -		offset = generic_file_llseek(file, offset, origin);
> -		goto out;
> -	case SEEK_DATA:
> -	case SEEK_HOLE:
> -		if (offset >= i_size_read(inode)) {
> -			mutex_unlock(&inode->i_mutex);
> -			return -ENXIO;
> -		}
> +	if (offset >= i_size_read(inode)) {
> +		mutex_unlock(&inode->i_mutex);
> +		return -ENXIO;
> +	}
>  
> -		ret = find_desired_extent(inode, &offset, origin);
> -		if (ret) {
> -			mutex_unlock(&inode->i_mutex);
> -			return ret;
> -		}
> +	ret = find_desired_extent(inode, &offset, origin);
> +	if (ret) {
> +		mutex_unlock(&inode->i_mutex);
> +		return ret;
>  	}
>  
>  	if (offset < 0 && !(file->f_mode & FMODE_UNSIGNED_OFFSET)) {
> -- 
> 1.7.6.409.ge7a85.dirty
> 
> --
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