drm/i915: Filter wake_flags passed to default_wake_function

(NOTE: This is the minimal backportable fix, a full fix is being
developed at https://patchwork.freedesktop.org/patch/388048/)

The flags passed to the wait_entry.func are passed onwards to
try_to_wake_up(), which has a very particular interpretation for its
wake_flags. In particular, beyond the published WF_SYNC, it has a few
internal flags as well. Since we passed the fence->error down the chain
via the flags argument, these ended up in the default_wake_function
confusing the kernel/sched.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/2110
Fixes: ef46884 ("drm/i915: Propagate fence errors")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Cc: <stable@vger.kernel.org> # v5.4+
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200728152144.1100-1-chris@chris-wilson.co.uk
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[Joonas: Rebased and reordered into drm-intel-gt-next branch]
[Joonas: Added a note and link about more complete fix]
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

drivers/gpu/drm/i915/i915_sw_fence.c

@@ -164,9 +164,13 @@ static void __i915_sw_fence_wake_up_all(struct i915_sw_fence *fence,
 
 		do {
 			list_for_each_entry_safe(pos, next, &x->head, entry) {
-				pos->func(pos,
-					  TASK_NORMAL, fence->error,
-					  &extra);
+				int wake_flags;
+
+				wake_flags = fence->error;
+				if (pos->func == autoremove_wake_function)
+					wake_flags = 0;
+
+				pos->func(pos, TASK_NORMAL, wake_flags, &extra);
 			}
 
 			if (list_empty(&extra))