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

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Message-ID: <a54329d5-a128-3ccd-7a12-f6cadaa20dbf@kernel.dk>
Date:   Fri, 18 Oct 2019 08:37:37 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Jann Horn <jannh@...gle.com>
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 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;                                   
}

-- 
Jens Axboe