Re: Racy loop device reuse logic

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On Wed, Jan 19, 2022 at 10:34:15PM +0100, Jan Kara wrote:
> On Wed 19-01-22 20:30:52, Tetsuo Handa wrote:
> > I found a way to avoid this race by splitting lo_open() into two phases
> > using task_work_add().  Christoph Hellwig is trying to take a look at
> > https://lkml.kernel.org/r/f6b947d0-1047-66b3-0243-af5017c9ab55@xxxxxxxxxxxxxxxxxxx
> > .
> 
> No, you have found a way to make the race window for mount(8) smaller. And
> I still disagree with that kernel change because it is making kernel more
> complex only to make the race window smaller. On another machine or with
> different scheduling decisions, you can still hit this race. This problem
> must be fixed in mount...

+1

I think Jan is right. In this case mount(8) is not robust enough. It
reads info about the device from /sys and then it opens the device.
Unfortunately, whatever can happen before the open() call.

    Karel

-- 
 Karel Zak  <kzak@xxxxxxxxxx>
 http://karelzak.blogspot.com




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