linux-kernel - Re: [RFC PATCH] io_uring: add support for IORING_OP

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Date:   Sun, 24 Jan 2021 01:59:05 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Andres Freund <andres@...razel.de>
Cc:     Lennert Buytenhek <buytenh@...tstofly.org>,
        Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        io-uring@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-btrfs@...r.kernel.org
Subject: Re: [RFC PATCH] io_uring: add support for IORING_OP_GETDENTS64

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.)