On Tue, Mar 14, 2017 at 10:13:37AM +0100, Christian König wrote: > Am 14.03.2017 um 09:45 schrieb Daniel Vetter: > >On Tue, Mar 14, 2017 at 10:50:51AM +1000, Dave Airlie wrote: > >>From: Dave Airlie <airlied at redhat.com> > >> > >>This isn't needed currently, but to reuse sync file for Vulkan > >>permanent shared semaphore semantics, we need to be able to swap > >>the fence backing a sync file. This patch adds a mutex to the > >>sync file and uses to protect accesses to the fence and cb members. > >> > >>Signed-off-by: Dave Airlie <airlied at redhat.com> > >We've gone to pretty great lengths to rcu-protect all the fence stuff, so > >that a peek-only is entirely lockless. Can we haz the same for this pls? > > Yes, just wanted to suggest the same thing. > > Basically you just need the following to retrieve the fence: > > while (sync_file->fence && !(fence = fence_get_rcu(sync_file->fence)); We even have a helper for that: fence = dma_fence_get_rcu_safe(&sync_file->fence); (Still going to suggest using a reservation_object rather than an exclusive-only implementation.) -Chris -- Chris Wilson, Intel Open Source Technology Centre
