Date: Mon, 10 Oct 2016 17:07:45 +1100
From: Dave Chinner <david@fromorbit.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>, Waiman Long <Waiman.Long@hpe.com>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        linux-alpha@vger.kernel.org, linux-ia64@vger.kernel.org,
        linux-s390@vger.kernel.org, linux-arch@vger.kernel.org,
        linux-doc@vger.kernel.org, Jason Low <jason.low2@hp.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Scott J Norton <scott.norton@hpe.com>,
        Douglas Hatch <doug.hatch@hpe.com>
Subject: Re: [RFC PATCH-tip v4 02/10] locking/rwsem: Stop active read lock
 ASAP
Message-ID: <20161010060745.GA27872@dastard>
References: <1471554672-38662-1-git-send-email-Waiman.Long@hpe.com>
 <1471554672-38662-3-git-send-email-Waiman.Long@hpe.com>
 <20161006181718.GA14967@linux-80c1.suse>
 <20161006214751.GU27872@dastard>
 <20161009151748.GA29102@infradead.org>
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On Sun, Oct 09, 2016 at 08:17:48AM -0700, Christoph Hellwig wrote:
> On Fri, Oct 07, 2016 at 08:47:51AM +1100, Dave Chinner wrote:
> > Except that it's DAX, and in 4.7-rc1 that used shared locking at the
> > XFS level and never took exclusive locks.
> > 
> > *However*, the DAX IO path locking in XFS  has changed in 4.9-rc1 to
> > match the buffered IO single writer POSIX semantics - the test is a
> > bad test based on the fact it exercised a path that is under heavy
> > development and so can't be used as a regression test across
> > multiple kernels.
> 
> That being said - I wonder if we should allow the shared lock on DAX
> files IFF the user is specifying O_DIRECT in the open mode..

It should do - if it doesn't then we screwed up the IO path
selection logic in XFS and we'll need to fix it.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com