Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider: - [High] gpu/buddy: block_incompatible() mishandles split and mixed blocks in __alloc_range_bias() --
commit 6dff7f0e6dce9c68ecb98f2d911199843d2b4401 Author: Arunpravin Paneer Selvam <[email protected]> gpu/buddy: restore two-pass clear/dirty guard for range-biased allocation This commit introduces a two-pass search in __gpu_buddy_alloc_range_bias() using block_incompatible() in the strict pass to prevent range-restricted allocations from splitting opposite-class (clear vs. dirty) blocks unless no matching blocks exist in the range. > diff --git a/drivers/gpu/buddy.c b/drivers/gpu/buddy.c > index 503f7d5934e4b..91935c71c5255 100644 > --- a/drivers/gpu/buddy.c > +++ b/drivers/gpu/buddy.c > @@ -1240,11 +1240,19 @@ 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; > + > + return needs_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 +1304,9 @@ __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 +1324,8 @@ __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] Does calling block_incompatible() on every visited node in __alloc_range_bias() before checking whether the block is split or mixed mishandle internal GPU_BUDDY_SPLIT nodes and coalesced GPU_BLOCK_MIXED free blocks? First, when mark_split() transitions a block to GPU_BUDDY_SPLIT, it leaves the previous GPU_BUDDY_HEADER_CLEAR bit intact on the internal node: drivers/gpu/buddy.c:mark_split() { block->header &= ~GPU_BUDDY_HEADER_STATE; block->header |= GPU_BUDDY_SPLIT; ... } Because gpu_buddy_init() initializes roots as dirty, any root or ancestor split while dirty keeps gpu_buddy_block_is_clear(block) == false while any descendant remains allocated. Conversely, a clear block that is split and later has a descendant freed as dirty keeps gpu_buddy_block_is_clear(block) == true on the split ancestor. When __gpu_buddy_alloc_range_bias() runs the first pass (fallback = false), __alloc_range_bias() evaluates block_incompatible(block, flags) on those GPU_BUDDY_SPLIT ancestors and skips the entire subtree without descending into its children. If no other root satisfies the request, the first pass returns -ENOSPC and __gpu_buddy_alloc_range_bias() falls back to the second pass (fallback = true), where block_incompatible() is disabled and the clear/has_clear child-ordering preference has been removed, causing the search to split the highest-address extent regardless of class. Second, __gpu_buddy_free() coalesces adjacent clear and dirty free buddies into a single GPU_BUDDY_FREE block with state GPU_BLOCK_MIXED, which has gpu_buddy_block_is_clear(block) == false and block->has_clear == true: 1. For clear range allocations (flags & GPU_BUDDY_CLEAR_ALLOCATION), Pass 1 sees gpu_buddy_block_is_clear(block) == false on a GPU_BLOCK_MIXED block and skips it via block_incompatible() without splitting it to reach the clear sub-blocks inside. Pass 2 then splits the mixed block without clear child-steering and unconditionally visits block->right first, returning a dirty block whenever the clear half is in block->left. 2. For dirty range allocations (!(flags & GPU_BUDDY_CLEAR_ALLOCATION)), block_incompatible() returns false on a higher-order GPU_BLOCK_MIXED block because gpu_buddy_block_is_clear(block) is false. Pass 1 then calls split_block(mm, block), which reclassifies block->left and block->right via mark_free(). If the child overlapping [start, end) is clear while the dirty child lies outside [start, end), Pass 1 rejects the clear child via block_incompatible() and skips the other child without calling __gpu_buddy_undo_splits(). Wouldn't leaving that split GPU_BLOCK_MIXED block unmerged keep both children in GPU_BUDDY_FREE state, preventing ancestor coalescing on teardown and triggering gpu_buddy_assert(gpu_buddy_block_is_free(mm->roots[i])) while leaking the split child gpu_buddy_block structures in gpu_buddy_fini()? [ ... ] -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
