linux-kernel - Re: [PATCH] fs: push i_mutex and filemap_write_and

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Date:	Wed, 29 Jun 2011 18:38:25 +0200
From:	Jan Kara <jack@...e.cz>
To:	Josef Bacik <josef@...hat.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	viro@...IV.linux.org.uk, hch@...radead.org
Subject: Re: [PATCH] fs: push i_mutex and filemap_write_and_wait down into
 ->fsync() handlers

On Tue 28-06-11 11:35:10, Josef Bacik wrote:
> Btrfs needs to be able to control how filemap_write_and_wait_range() is called
> in fsync to make it less of a painful operation, so push down taking i_mutex and
> the calling of filemap_write_and_wait() down into the ->fsync() handlers.  Some
> file systems can drop taking the i_mutex altogether it seems, like ext3 and
> ocfs2.  For correctness sake I just pushed everything down in all cases to make
> sure that we keep the current behavior the same for everybody, and then each
> individual fs maintainer can make up their mind about what to do from there.
> Thanks,
> 
> Signed-off-by: Josef Bacik <josef@...hat.com>
...
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 1921392..fa44df8 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -1758,7 +1758,7 @@ extern int ext4_htree_store_dirent(struct file *dir_file, __u32 hash,
>  extern void ext4_htree_free_dir_info(struct dir_private_info *p);
>  
>  /* fsync.c */
> -extern int ext4_sync_file(struct file *, int);
> +extern int ext4_sync_file(struct file *, loff_t, loff_t, int);
>  extern int ext4_flush_completed_IO(struct inode *);
>  
>  /* hash.c */
> diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
> index ce66d2f..afab2e4 100644
> --- a/fs/ext4/fsync.c
> +++ b/fs/ext4/fsync.c
> @@ -165,7 +165,7 @@ static int ext4_sync_parent(struct inode *inode)
>   * i_mutex lock is held when entering and exiting this function
>   */
>  
> -int ext4_sync_file(struct file *file, int datasync)
> +int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
>  {
>  	struct inode *inode = file->f_mapping->host;
>  	struct ext4_inode_info *ei = EXT4_I(inode);
> @@ -178,15 +178,22 @@ int ext4_sync_file(struct file *file, int datasync)
>  
>  	trace_ext4_sync_file_enter(file, datasync);
>  
> +	ret = filemap_write_and_wait_range(inode->i_mapping, start, end);
> +	if (ret)
> +		return ret;
> +	mutex_lock(&inode->i_mutex);
> +
>  	if (inode->i_sb->s_flags & MS_RDONLY)
> -		return 0;
> +		goto out;
>  
>  	ret = ext4_flush_completed_IO(inode);
>  	if (ret < 0)
>  		goto out;
>  
>  	if (!journal) {
> -		ret = generic_file_fsync(file, datasync);
> +		if (inode->i_state & I_DIRTY ||
> +		    (datasync && (inode->i_state & I_DIRTY_DATASYNC)))
> +			ret = sync_inode_metadata(inode, 1);
  Umm, how did you get to this change? It is actually wrong - ext4 in
nojournal mode really seems to need to call generic_file_fsync() (so that
sync_buffers_list() is called).

>  		if (!ret && !list_empty(&inode->i_dentry))
>  			ret = ext4_sync_parent(inode);
>  		goto out;
> @@ -220,6 +227,7 @@ int ext4_sync_file(struct file *file, int datasync)
>  	if (needs_barrier)
>  		blkdev_issue_flush(inode->i_sb->s_bdev, GFP_KERNEL, NULL);
>   out:
> +	mutex_unlock(&inode->i_mutex);
>  	trace_ext4_sync_file_exit(inode, ret);
>  	return ret;
>  }

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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