loader/dri3: Do not wait for source buffer for prefilling unless front.

The source buffer should have been just swapped off and should already
be okay to blit from without any further synchronization unless it is
the front buffer.

If the server has flipped the buffer instead of copied it, then the fence
is not triggered until the frame is idled after the next frame is displayed.
However, the next frame cannot be presented since the back buffer preparation
is blocked on the source fence and deadlock occurs.

Signed-off-by: David Riley <davidriley@chromium.org>
47 jobs for !4718 with flip-deadlock
latest detached
Status Job ID Name Coverage
  Container
manual arm_build #2458276
aarch64 manual
manual arm_test #2458278
aarch64 manual
manual windows_build_vs2019 #2458280
windows shell 1809 mesa manual
manual x86_build #2458269
manual
manual x86_build_old #2458274
manual
manual x86_test-gl #2458271
manual
manual x86_test-vk #2458272
manual
 
  Meson X86 64
created meson-clang #2458287
created meson-classic #2458285
created meson-clover #2458288
created meson-clover-old-llvm #2458290
created meson-gallium #2458283
created meson-testing #2458282
created meson-vulkan #2458291
 
  Scons
created scons-win64 #2458293
allowed to fail
 
  Meson Misc
created meson-arm64 #2458297
aarch64
created meson-arm64-build-test #2458299
aarch64
created meson-armhf #2458295
aarch64
created meson-i386 #2458302
created meson-mingw32-x86_64 #2458305
created meson-ppc64el #2458304
kvm
created meson-s390x #2458303
kvm
created meson-windows-vs2019 #2458301
windows docker 1809 mesa
 
  Llvmpipe
created llvmpipe-gles2 #2458309
created llvmpipe-traces #2458310
created piglit-glslparser #2458307
created piglit-quick_gl #2458306
created piglit-quick_shader #2458308
 
  Softpipe
created softpipe-gles2 #2458311
created softpipe-gles31 1/4 #2458314
created softpipe-gles3 1/2 #2458312
created softpipe-gles31 2/4 #2458315
created softpipe-gles31 3/4 #2458316
created softpipe-gles31 4/4 #2458317
created softpipe-gles3 2/2 #2458313
 
  Freedreno
created arm64_a306_gles2 #2458321
google-freedreno-db410c
created arm64_a530_gles2 #2458322
google-freedreno-db820c
created arm64_a630_gles2 #2458318
mesa-cheza
created arm64_a630_gles3 #2458320
mesa-cheza
created arm64_a630_gles31 #2458319
mesa-cheza
 
  Panfrost
created panfrost-t720-gles2:arm64 #2458323
mesa-ci-aarch64-lava-collabora
created panfrost-t760-gles2:armhf #2458324
mesa-ci-aarch64-lava-collabora
created panfrost-t860-gles2:arm64 #2458325
mesa-ci-aarch64-lava-collabora
created panfrost-t860-gles3:arm64 #2458326
mesa-ci-aarch64-lava-collabora
 
  Radv
created radv-fossils #2458327
 
  Virgl
created virgl-gles2 #2458328
created virgl-gles3 #2458329