Re: [RFC PATCH 03/11] vfs: Use init_kiocb() to initialise new IOCBs

From: Jens Axboe <axboe@kernel.dk>
To: David Howells <dhowells@redhat.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@infradead.org>
Cc: Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
	Jeff Layton <jlayton@kernel.org>,
	David Hildenbrand <david@redhat.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	Logan Gunthorpe <logang@deltatee.com>,
	Hillf Danton <hdanton@sina.com>,
	Christian Brauner <brauner@kernel.org>,
	linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Christoph Hellwig <hch@lst.de>,
	Christian Brauner <christian@brauner.io>
Subject: Re: [RFC PATCH 03/11] vfs: Use init_kiocb() to initialise new IOCBs
Date: Fri, 30 Jun 2023 09:39:30 -0600	[thread overview]
Message-ID: <36eda01e-502e-b93d-9098-77ed5a16f33c@kernel.dk> (raw)
In-Reply-To: <20230630152524.661208-4-dhowells@redhat.com>

On 6/30/23 9:25?AM, David Howells wrote:
> diff --git a/io_uring/rw.c b/io_uring/rw.c
> index 1bce2208b65c..1cade1567162 100644
> --- a/io_uring/rw.c
> +++ b/io_uring/rw.c
> @@ -655,12 +655,13 @@ static bool need_complete_io(struct io_kiocb *req)
>  		S_ISBLK(file_inode(req->file)->i_mode);
>  }
>  
> -static int io_rw_init_file(struct io_kiocb *req, fmode_t mode)
> +static int io_rw_init_file(struct io_kiocb *req, unsigned int io_direction)
>  {
>  	struct io_rw *rw = io_kiocb_to_cmd(req, struct io_rw);
>  	struct kiocb *kiocb = &rw->kiocb;
>  	struct io_ring_ctx *ctx = req->ctx;
>  	struct file *file = req->file;
> +	fmode_t mode = (io_direction == WRITE) ? FMODE_WRITE : FMODE_READ;
>  	int ret;
>  
>  	if (unlikely(!file || !(file->f_mode & mode)))

Not ideal to add a branch here, probably better to just pass in both?

> @@ -870,7 +871,7 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
>  		iov_iter_restore(&s->iter, &s->iter_state);
>  		iovec = NULL;
>  	}
> -	ret = io_rw_init_file(req, FMODE_WRITE);
> +	ret = io_rw_init_file(req, WRITE);
>  	if (unlikely(ret)) {
>  		kfree(iovec);
>  		return ret;
> @@ -914,7 +915,6 @@ int io_write(struct io_kiocb *req, unsigned int issue_flags)
>  		__sb_writers_release(file_inode(req->file)->i_sb,
>  					SB_FREEZE_WRITE);
>  	}
> -	kiocb->ki_flags |= IOCB_WRITE;
>  
>  	if (likely(req->file->f_op->write_iter))
>  		ret2 = call_write_iter(req->file, kiocb, &s->iter);
> 

One concern here is that we're using IOCB_WRITE here to tell if
sb_start_write() has been done or not, and hence whether
kiocb_end_write() needs to be called. You know set it earlier, which
means if we get a failure if we need to setup async data, then we know
have IOCB_WRITE set at that point even though we did not call
sb_start_write().

-- 
Jens Axboe