Re: [RFC PATCH-tip v4 02/10] locking/rwsem: Stop active read lock ASAP

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:

quoted

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