tree cd99c51628ae8ca73fdc34674f139d516215c61d
parent 4dda41d3d76747414586a4bad5615b550e0986b1
author Alex Elder <elder@inktank.com> 1361463006 -0600
committer Alex Elder <elder@inktank.com> 1361828210 -0600

rbd: barriers are hard

Let's go shopping!

I'm afraid this may not have gotten it right:
    07741308  rbd: add barriers near done flag operations

The smp_wmb() should have been done *before* setting the done flag,
to ensure all other data was valid before marking the object request
done.

Switch to use atomic_inc_return() here to set the done flag, which
allows us to verify we don't mark something done more than once.
Doing this also implies general barriers before and after the call.

And although a read memory barrier might have been sufficient before
reading the done flag, convert this to a full memory barrier just
to put this issue to bed.

This resolves:
    http://tracker.ceph.com/issues/4238

Signed-off-by: Alex Elder <elder@inktank.com>
Reviewed-by: Josh Durgin <josh.durgin@inktank.com>