netdev - Re: [PATCH 1/3] io_uring: add support for async work inheriting files table

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Date:   Fri, 18 Oct 2019 16:40:17 +0200
From:   Jann Horn <jannh@...gle.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/3] io_uring: add support for async work inheriting files table

On Fri, Oct 18, 2019 at 4:37 PM Jens Axboe <axboe@...nel.dk> wrote:
>
> On 10/18/19 8:34 AM, Jann Horn wrote:
> > On Fri, Oct 18, 2019 at 4:01 PM Jens Axboe <axboe@...nel.dk> wrote:
> >> On 10/17/19 8:41 PM, Jann Horn wrote:
> >>> On Fri, Oct 18, 2019 at 4:01 AM Jens Axboe <axboe@...nel.dk> wrote:
> >>>> This is in preparation for adding opcodes that need to modify files
> >>>> in a process file table, either adding new ones or closing old ones.
> > [...]
> >> Updated patch1:
> >>
> >> http://git.kernel.dk/cgit/linux-block/commit/?h=for-5.5/io_uring-test&id=df6caac708dae8ee9a74c9016e479b02ad78d436
> >
> > I don't understand what you're doing with old_files in there. In the
> > "s->files && !old_files" branch, "current->files = s->files" happens
> > without holding task_lock(), but current->files and s->files are also
> > the same already at that point anyway. And what's the intent behind
> > assigning stuff to old_files inside the loop? Isn't that going to
> > cause the workqueue to keep a modified current->files beyond the
> > runtime of the work?
>
> I simply forgot to remove the old block, it should only have this one:
>
> if (s->files && s->files != cur_files) {
>         task_lock(current);
>         current->files = s->files;
>         task_unlock(current);
>         if (cur_files)
>                 put_files_struct(cur_files);
>         cur_files = s->files;
> }

Don't you still need a put_files_struct() in the case where "s->files
== cur_files"?