linux-kernel - Re: [PATCH] fuse: hold i_mutex in fuse_file

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Date:	Wed, 12 Jun 2013 07:40:22 -0400
From:	Brian Foster <bfoster@...hat.com>
To:	Maxim Patlasov <MPatlasov@...allels.com>
CC:	miklos@...redi.hu, fuse-devel@...ts.sourceforge.net,
	avati@...hat.com, linux-kernel@...r.kernel.org, devel@...nvz.org
Subject: Re: [PATCH] fuse: hold i_mutex in fuse_file_fallocate()

On 06/11/2013 06:59 AM, Maxim Patlasov wrote:
> Changing size of a file on server and local update (fuse_write_update_size)
> should be always protected by inode->i_mutex. Otherwise a race like this is
> possible:
> 
> 1. Process 'A' calls fallocate(2) to extend file (~FALLOC_FL_KEEP_SIZE).
> fuse_file_fallocate() sends FUSE_FALLOCATE request to the server.
> 2. Process 'B' performs ordinary buffered write(2) with a length big enough
> to extend the file beyond "offset + length" of fallocate call.
> 3. Process 'A' resumes execution of fuse_file_fallocate() and calls
> fuse_write_update_size(inode, offset + length). But 'offset + length' was
> obsoleted by write from previous step.
> 

Hi Maxim,

Doesn't fuse_write_update_size() already handle this particular case by
only ever extending the size?

Brian

> Signed-off-by: Maxim V. Patlasov <MPatlasov@...allels.com>
> ---
>  fs/fuse/file.c |   10 ++++++----
>  1 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index e570081..8dfbf7d 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -2470,14 +2470,16 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
>  		.mode = mode
>  	};
>  	int err;
> +	bool lock_inode = !(mode & FALLOC_FL_KEEP_SIZE) ||
> +			   (mode & FALLOC_FL_PUNCH_HOLE);
>  
>  	if (fc->no_fallocate)
>  		return -EOPNOTSUPP;
>  
> -	if (mode & FALLOC_FL_PUNCH_HOLE) {
> +	if (lock_inode)
>  		mutex_lock(&inode->i_mutex);
> +	if (mode & FALLOC_FL_PUNCH_HOLE)
>  		fuse_set_nowrite(inode);
> -	}
>  
>  	req = fuse_get_req_nopages(fc);
>  	if (IS_ERR(req)) {
> @@ -2511,10 +2513,10 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
>  	fuse_invalidate_attr(inode);
>  
>  out:
> -	if (mode & FALLOC_FL_PUNCH_HOLE) {
> +	if (mode & FALLOC_FL_PUNCH_HOLE)
>  		fuse_release_nowrite(inode);
> +	if (lock_inode)
>  		mutex_unlock(&inode->i_mutex);
> -	}
>  
>  	return err;
>  }
> 

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