linux-kernel - Re: [PATCH v2 13/17] locks: remove i_have_this_lease check from __break

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Date:	Thu, 4 Sep 2014 14:03:03 -0400
From:	Jeff Layton <jeff.layton@...marydata.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org,
	"J. Bruce Fields" <bfields@...ldses.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 13/17] locks: remove i_have_this_lease check from
 __break_lease

On Thu, 4 Sep 2014 10:51:32 -0700
Christoph Hellwig <hch@...radead.org> wrote:

> On Thu, Sep 04, 2014 at 08:38:39AM -0400, Jeff Layton wrote:
> > I think that the intent of this code was to ensure that a process won't
> > deadlock if it has one fd open with a lease on it and then breaks that
> > lease by opening another fd. In that case it'll treat the __break_lease
> > call as if it were non-blocking.
> > 
> > This seems wrong -- the process could (for instance) be multithreaded
> > and managing different fds via different threads. I also don't see any
> > mention of this limitation in the (somewhat sketchy) documentation.
> > 
> > Remove the check and the non-blocking behavior when i_have_this_lease
> > is true.
> 
> This looks reasonable to me, but I'm always very worried about changing
> userspace exposed behavior..
> 

Yeah, me too, but I think the behavior in this case is just plain
wrong. It's really hard to understand how anyone would rely on this to
avoid deadlocking, but you never know...

I want to phase this out, but I'm certainly open to doing this in a
smoother fashion if anyone has suggestions on how to do so.

Thanks,
-- 
Jeff Layton <jlayton@...marydata.com>
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