Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [High] gpu/buddy: leaked split on range-straddling mixed block in __alloc_range_bias() --
commit caf65a7be15ef66d98faecfc731749477d23b658 Author: Arunpravin Paneer Selvam <[email protected]> gpu/buddy: restore two-pass clear/dirty guard for range-biased allocation This commit introduces a two-pass clear/dirty eligibility check in __alloc_range_bias() via block_incompatible() so that range-biased allocations avoid splitting opposite-class extents during the initial strict pass before falling back when -ENOSPC is returned. It also accepts mixed blocks at the requested order as-is and adds a KUnit regression test for range-biased clear/dirty separation. > diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c > index 28cff97d57dc8..f2914f919b04a 100644 > --- a/drivers/gpu/buddy.c > +++ b/drivers/gpu/buddy.c > @@ -1240,11 +1240,23 @@ static void __gpu_buddy_undo_splits(struct gpu_buddy > *mm, > } > } > > +static bool block_incompatible(struct gpu_buddy_block *block, unsigned int > flags) > +{ > + bool needs_clear = flags & GPU_BUDDY_CLEAR_ALLOCATION; > + > + if (!gpu_buddy_block_is_free(block)) > + return false; > + > + return needs_clear ? !block->has_clear : > + gpu_buddy_block_is_clear(block); > +} > + > static struct gpu_buddy_block * > __alloc_range_bias(struct gpu_buddy *mm, > u64 start, u64 end, > unsigned int order, > - unsigned long flags) > + unsigned long flags, > + bool fallback) > { [ ... ] > @@ -1298,6 +1308,9 @@ __alloc_range_bias(struct gpu_buddy *mm, > continue; > } > > + if (!fallback && block_incompatible(block, flags)) > + continue; > + > if (contains(start, end, block_start, block_end) && > order == gpu_buddy_block_order(block)) { > /* > @@ -1315,38 +1328,8 @@ __alloc_range_bias(struct gpu_buddy *mm, > goto err_undo; > } > > - /* > - * Top-down is a strict address-placement policy, so when it is > - * requested we ignore clear steering and simply descend the > - * right (higher-address) child first. Only a non-top-down clear > - * request biases the descent towards clear/has_clear subtrees. > - */ > - if ((flags & GPU_BUDDY_CLEAR_ALLOCATION) && > - !(flags & GPU_BUDDY_TOPDOWN_ALLOCATION)) { > - struct gpu_buddy_block *prefer; > - > - if (gpu_buddy_block_is_clear(block->right)) > - prefer = block->right; > - else if (gpu_buddy_block_is_clear(block->left)) > - prefer = block->left; > - else if (block->right->has_clear) > - prefer = block->right; > - else if (block->left->has_clear) > - prefer = block->left; > - else > - prefer = block->right; > - > - if (prefer == block->right) { > - list_add(&block->left->tmp_link, &dfs); > - list_add(&block->right->tmp_link, &dfs); > - } else { > - list_add(&block->right->tmp_link, &dfs); > - list_add(&block->left->tmp_link, &dfs); > - } > - } else { > - list_add(&block->left->tmp_link, &dfs); > - list_add(&block->right->tmp_link, &dfs); > - } > + list_add(&block->left->tmp_link, &dfs); > + list_add(&block->right->tmp_link, &dfs); > } while (1); [Severity: High] Can __alloc_range_bias() still leave an unmerged split block (and leak the child gpu_buddy_block allocations on teardown) when a free mixed block of order greater than the target order straddles the start or end boundary of the requested [start, end) range? In __alloc_range_bias(), block_incompatible() returns false for any free mixed block because block->has_clear is true and gpu_buddy_block_is_clear() is false across the whole block span. Dropping unsplit_block() relies on the assumption that splitting a mixed block during the strict pass (fallback == false) will always find at least one compatible descendant at the target order. However, when a free mixed block with order > target order only partially overlaps [start, end), it passes the adjusted range check in __alloc_range_bias(): 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 (!fallback && block_incompatible(block, flags)) continue; ... if (!gpu_buddy_block_is_split(block)) { err = split_block(mm, block); if (unlikely(err)) goto err_undo; } If the compatible portion that made the parent mixed lies in the child outside [start, end) while the child inside [start, end) is purely opposite-class (for example, clear when a dirty allocation is requested), split_block() splits the parent into two free children, the out-of-range child is skipped by the range check, and the in-range child is rejected by block_incompatible(). When the allocation is then satisfied elsewhere in the tree, the split parent is left in GPU_BUDDY_SPLIT state with both children simultaneously in GPU_BUDDY_FREE state: 1. If the mixed block straddles end (e.g. a 4 MiB allocator with 1 MiB chunks where [0, 1M) is dirty free, [1M, 2M) is allocated, and [2M, 4M) is a coalesced free mixed block with [2M, 3M) clear and [3M, 4M) dirty), a 1 MiB dirty range allocation over [0, 3M) visits [2M, 4M) first, splits it, rejects [3M, 4M) as out of range and [2M, 3M) via block_incompatible(), and then succeeds at [0, 1M) during the strict pass without running the fallback pass. 2. If the mixed block straddles start (e.g. [0, 2M) is a free mixed block with [0, 1M) dirty and [1M, 2M) clear, and [2M, 4M) is clear free), a 1 MiB dirty range allocation over [1M, 4M) skips [2M, 4M) in the strict pass, splits [0, 2M) and rejects both halves, fails the strict pass with -ENOSPC, and then satisfies the request from [3M, 4M) in the fallback pass before visiting [0, 2M). Because neither child of the abandoned split node is allocated, freeing other blocks never coalesces across the GPU_BUDDY_SPLIT parent in __gpu_buddy_free(), leaving the buddy tree permanently fragmented and triggering gpu_buddy_assert(gpu_buddy_block_is_free(mm->roots[i])) in gpu_buddy_fini() while leaking the descendant gpu_buddy_block structures in slab_blocks. Should __alloc_range_bias() still undo rejected splits when descending blocks that are not fully contained within [start, end), or check compatibility against the in-range portion? -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
