Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Sun, 24 Jan 2021 01:59:05 +0000
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     Andres Freund <andres@anarazel.de>
Cc:     Lennert Buytenhek <buytenh@wantstofly.org>,
        Jens Axboe <axboe@kernel.dk>, linux-kernel@vger.kernel.org,
        io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-btrfs@vger.kernel.org
Subject: Re: [RFC PATCH] io_uring: add support for IORING_OP_GETDENTS64
Message-ID: <20210124015905.GH740243@zeniv-ca>
References: <20210123114152.GA120281@wantstofly.org>
 <20210123235055.azmz5jm2lwyujygc@alap3.anarazel.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20210123235055.azmz5jm2lwyujygc@alap3.anarazel.de>
Sender: Al Viro <viro@ftp.linux.org.uk>
Precedence: bulk

On Sat, Jan 23, 2021 at 03:50:55PM -0800, Andres Freund wrote:

> As there's only a shared lock, seems like both would end up with the
> same ctx->pos and end up updating f_pos to the same offset (assuming the
> same count).
> 
> Am I missing something?

This:
        f = fdget_pos(fd);
        if (!f.file)
                return -EBADF;
in the callers.  Protection of struct file contents belongs to struct file,
*not* struct inode.  Specifically, file->f_pos_lock.  *IF* struct file
in question happens to be shared and the file is a regular or directory
(sockets don't need any exclusion on read(2), etc.)