linux-kernel - Re: [PATCH] fuse: hold i_mutex in fuse_file_fallocate()

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Date:	Thu, 13 Jun 2013 07:46:00 -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() - v2

On 06/13/2013 04:16 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' calls ftruncate(2) shrinking the file. fuse_do_setattr()
> sends shrinking FUSE_SETATTR request to the server and updates local i_size
> by i_size_write(inode, outarg.attr.size).
> 3. Process 'A' resumes execution of fuse_file_fallocate() and calls
> fuse_write_update_size(inode, offset + length). But 'offset + length' was
> obsoleted by ftruncate from previous step.
> 
> Changed in v2 (thanks Brian and Anand for suggestions):
>  - made relation between mutex_lock() and fuse_set_nowrite(inode) more
>    explicit and clear.
>  - updated patch description to use ftruncate(2) in example
> 
> Signed-off-by: Maxim V. Patlasov <MPatlasov@...allels.com>
> ---

Makes more sense and I like the cleanup... thanks.

Reviewed-by: Brian Foster <bfoster@...hat.com>

>  fs/fuse/file.c |   12 ++++++++----
>  1 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index e570081..35f2810 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -2470,13 +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);
> -		fuse_set_nowrite(inode);
> +		if (mode & FALLOC_FL_PUNCH_HOLE)
> +			fuse_set_nowrite(inode);
>  	}
>  
>  	req = fuse_get_req_nopages(fc);
> @@ -2511,8 +2514,9 @@ static long fuse_file_fallocate(struct file *file, int mode, loff_t offset,
>  	fuse_invalidate_attr(inode);
>  
>  out:
> -	if (mode & FALLOC_FL_PUNCH_HOLE) {
> -		fuse_release_nowrite(inode);
> +	if (lock_inode) {
> +		if (mode & FALLOC_FL_PUNCH_HOLE)
> +			fuse_release_nowrite(inode);
>  		mutex_unlock(&inode->i_mutex);
>  	}
>  
> 

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