[PATCH v2 1/3] drm/buddy: fix range bias

[Matthew Auld]

There is a corner case here where start/end is after/before the block
range we are currently checking. If so we need to be sure that splitting
the block will eventually give use the block size we need. To do that we
should adjust the block range to account for the start/end, and only
continue with the split if the size/alignment will fit the requested
size. Not doing so can result in leaving split blocks unmerged when it
eventually fails.

Fixes: afea229fe102 ("drm: improve drm_buddy_alloc function")
Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam at amd.com>
Cc: Christian König <christian.koenig at amd.com>
Cc: <stable at vger.kernel.org> # v5.18+
Reviewed-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam at amd.com>
---
 drivers/gpu/drm/drm_buddy.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/gpu/drm/drm_buddy.c b/drivers/gpu/drm/drm_buddy.c
index c4222b886db7..f3a6ac908f81 100644
--- a/drivers/gpu/drm/drm_buddy.c
+++ b/drivers/gpu/drm/drm_buddy.c
@@ -332,6 +332,7 @@ alloc_range_bias(struct drm_buddy *mm,
 		 u64 start, u64 end,
 		 unsigned int order)
 {
+	u64 req_size = mm->chunk_size << order;
 	struct drm_buddy_block *block;
 	struct drm_buddy_block *buddy;
 	LIST_HEAD(dfs);
@@ -367,6 +368,15 @@ alloc_range_bias(struct drm_buddy *mm,
 		if (drm_buddy_block_is_allocated(block))
 			continue;
 
+		if (block_start < start || block_end > end) {
+			u64 adjusted_start = max(block_start, start);
+			u64 adjusted_end = min(block_end, end);
+
+			if (round_down(adjusted_end + 1, req_size) <=
+			    round_up(adjusted_start, req_size))
+				continue;
+		}
+
 		if (contains(start, end, block_start, block_end) &&
 		    order == drm_buddy_block_order(block)) {
 			/*
-- 
2.43.0