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Date: Thu, 7 Feb 2013 18:32:38 +0400
Message-ID: <CAKywueTmU_L5cwwJSoUY6753eHf_38VtHadZGt9tcLS59sqmOA@mail.gmail.com>
Subject: Re: [PATCH v2 3/8] vfs: Add O_DENYREAD/WRITE flags support for open syscall
From: Pavel Shilovsky <piastry@etersoft.ru>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org,
        wine-devel@winehq.org
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Sender: linux-nfs-owner@vger.kernel.org

2013/2/7 J. Bruce Fields <bfields@fieldses.org>:
> On Thu, Feb 07, 2013 at 01:53:46PM +0400, Pavel Shilovsky wrote:
>> Nothing prevents it. If somebody grabbed a share mode lock on a file
>> before we call deny_lock_file, we simply close this file and return
>> -ETXTBSY.
>
> But leave the newly-created file there--ugh.
>
>> We can't grab it before atomic_open because we don't have an
>> inode there.
>
> If you can get the lock while still holding the directory i_mutex can't
> you prevent anyone else from looking up the new file until you've gotten
> the lock?
>

Hm..., seems you are right, I missed this part:
mutex_lock
lookup_open -> atomic_open -> deny_lock_file
mutex_unlock

that means that nobody can open and of course set flock on the newly
created file (because flock is done through file descriptor). So, it
should be fine to call flock after f_ops->atomic_open in atomic_open
function. Thanks.

-- 
Best regards,
Pavel Shilovsky.