drm/amdkfd: Ensure consistent barrier state saved in gfx12 trap handler

drm/amdkfd: Ensure consistent barrier state saved in gfx12 trap handler

[ Upstream commit d584198a6fe4c51f4aa88ad72f258f8961a0f11c ]

It is possible for some waves in a workgroup to finish their save
sequence before the group leader has had time to capture the workgroup
barrier state.  When this happens, having those waves exit do impact the
barrier state.  As a consequence, the state captured by the group leader
is invalid, and is eventually incorrectly restored.

This patch proposes to have all waves in a workgroup wait for each other
at the end of their save sequence (just before calling s_endpgm_saved).

Signed-off-by: Lancelot SIX <lancelot.six@amd.com>
Reviewed-by: Jay Cornwall <jay.cornwall@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org # 6.12.x
Signed-off-by: Sasha Levin <sashal@kernel.org>