drm/buddy: Fix the range bias clear memory allocation issue

Problem statement: During the system boot time, an application request
for the bulk volume of cleared range bias memory when the clear_avail
is zero, we dont fallback into normal allocation method as we had an
unnecessary clear_avail check which prevents the fallback method leads
to fb allocation failure following system goes into unresponsive state.

Solution: Remove the unnecessary clear_avail check in the range bias
allocation function.

v2: add a kunit for this corner case (Daniel Vetter)
Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Fixes: 96950929 ("drm/buddy: Implement tracking clear page feature")
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240514145636.16253-1-Arunpravin.PaneerSelvam@amd.com

drivers/gpu/drm/drm_buddy.c

@@ -249,6 +249,7 @@ int drm_buddy_init(struct drm_buddy *mm, u64 size, u64 chunk_size)
 
 	mm->size = size;
 	mm->avail = size;
+	mm->clear_avail = 0;
 	mm->chunk_size = chunk_size;
 	mm->max_order = ilog2(size) - ilog2(chunk_size);
 
@@ -574,7 +575,7 @@ __drm_buddy_alloc_range_bias(struct drm_buddy *mm,
 
 	block = __alloc_range_bias(mm, start, end, order,
 				   flags, fallback);
-	if (IS_ERR(block) && mm->clear_avail)
+	if (IS_ERR(block))
 		return __alloc_range_bias(mm, start, end, order,
 					  flags, !fallback);