Re: [PATCH RFC] fuse: Prevent background write requests increase inode size

[Kirill Tkhai]

Hi, Miklos,

please take a look into two problems this patch points:

1)we have to set "io->async = false" in fuse_direct_IO(),
  when inode size is changed (we mustn't increase inode
  size in background);
2)we have to increment fi->writectr on all background requests.

Thanks,
Kirill

On 06.11.2018 17:02, Kirill Tkhai wrote:
> Hi, Miklos,
> 
> this is not a well-tested patch, this is a concept,
> showing the places, where it looks we have a problem.
> 
> Commit 7879c4e58b7c made io->async careless about inode size,
> and this is wrong. Asyncronuos background requests may be sent
> to userspace after inode becomes unlocked, when background
> queue is throttled. In this case we execute a write request
> extending inode size without any protection, and this ruines
> everything. Fix that.
> 
> Also, some write background requests do not increment fi->writectr,
> e.g.:
> 	fuse_direct_IO()
> 	  fuse_direct_io()
> 	    fuse_send_write()
> 	      fuse_async_req_send()
> 	        fuse_request_send_background()
> 
> This is a reason fuse_sync_writes() does not work as expected.
> Fix that too.
> 
> Signed-off-by: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx>
> ---
>  fs/fuse/file.c |   20 ++++++++++++++++++--
>  1 file changed, 18 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/fuse/file.c b/fs/fuse/file.c
> index cc2121b37bf5..0b71a3c96168 100644
> --- a/fs/fuse/file.c
> +++ b/fs/fuse/file.c
> @@ -610,6 +610,9 @@ static void fuse_aio_complete(struct fuse_io_priv *io, int err, ssize_t pos)
>  static void fuse_aio_complete_req(struct fuse_conn *fc, struct fuse_req *req)
>  {
>  	struct fuse_io_priv *io = req->io;
> +	struct kiocb *iocb = io->iocb;
> +	struct file *file = iocb->ki_filp;
> +	struct fuse_inode *fi = get_fuse_inode(file_inode(file));
>  	ssize_t pos = -1;
>  
>  	fuse_release_user_pages(req, io->should_dirty);
> @@ -625,6 +628,12 @@ static void fuse_aio_complete_req(struct fuse_conn *fc, struct fuse_req *req)
>  	}
>  
>  	fuse_aio_complete(io, req->out.h.error, pos);
> +
> +	if (io->write) {
> +		spin_lock(&fc->lock);
> +		fi->writectr--;
> +		spin_unlock(&fc->lock);
> +	}
>  }
>  
>  static size_t fuse_async_req_send(struct fuse_conn *fc, struct fuse_req *req,
> @@ -966,6 +975,7 @@ static size_t fuse_send_write(struct fuse_req *req, struct fuse_io_priv *io,
>  {
>  	struct kiocb *iocb = io->iocb;
>  	struct file *file = iocb->ki_filp;
> +	struct fuse_inode *fi = get_fuse_inode(file_inode(file));
>  	struct fuse_file *ff = file->private_data;
>  	struct fuse_conn *fc = ff->fc;
>  	struct fuse_write_in *inarg = &req->misc.write.in;
> @@ -981,8 +991,12 @@ static size_t fuse_send_write(struct fuse_req *req, struct fuse_io_priv *io,
>  		inarg->lock_owner = fuse_lock_owner_id(fc, owner);
>  	}
>  
> -	if (io->async)
> +	if (io->async) {
> +		spin_lock(&fc->lock);
> +		fi->writectr++;
> +		spin_unlock(&fc->lock);
>  		return fuse_async_req_send(fc, req, count, io);
> +	}
>  
>  	fuse_request_send(fc, req);
>  	return req->misc.write.out.size;
> @@ -2904,8 +2918,10 @@ fuse_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>  	 * We cannot asynchronously extend the size of a file.
>  	 * In such case the aio will behave exactly like sync io.
>  	 */
> -	if ((offset + count > i_size) && iov_iter_rw(iter) == WRITE)
> +	if ((offset + count > i_size) && iov_iter_rw(iter) == WRITE) {
>  		io->blocking = true;
> +		io->async = false;
> +	}
>  
>  	if (io->async && io->blocking) {
>  		/*
>