Re: RFC: hold i_rwsem until aio completes

[Dave Chinner]

On Mon, Feb 03, 2020 at 06:46:41PM +0100, Christoph Hellwig wrote:
> On Sat, Jan 18, 2020 at 08:28:38PM +1100, Dave Chinner wrote:
> > I think it's pretty gross, actually. It  makes the same mistake made
> > with locking in the old direct IO code - it encodes specific lock
> > operations via flags into random locations in the DIO path. This is
> > a very slippery slope, and IMO it is an layering violation to encode
> > specific filesystem locking smeantics into a layer that is supposed
> > to be generic and completely filesystem agnostic. i.e.  this
> > mechanism breaks if a filesystem moves to a different type of lock
> > (e.g. range locks), and history teaches us that we'll end up making
> > a horrible, unmaintainable mess to support different locking
> > mechanisms and contexts.
> > 
> > I think that we should be moving to a model where the filesystem
> > provides an unlock method in the iomap operations structure, and if
> > the method is present in iomap_dio_complete() it gets called for the
> > filesystem to unlock the inode at the appropriate point. This also
> > allows the filesystem to provide a different method for read or
> > write unlock, depending on what type of lock it held at submission.
> > This gets rid of the need for the iomap code to know what type of
> > lock the caller holds, too.
> 
> I'd rather avoid yet another method.  But I think with a little
> tweaking we can move the unlock into the ->end_io method.

That would work, too :)

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx