mas_skip_node() is used to move the maple state to the node with a higher limit. It does this by walking up the tree and increasing the slot count. Since slot count may not be able to be increased, it may need to walk up multiple times to find room to walk right to a higher limit node. The limit of slots that was being used was the node limit and not the last location of data in the node. This would cause the maple state to be shifted outside actual data and enter an error state, thus returning -EBUSY. The result of the incorrect error state means that mas_awalk() would return an error instead of finding the allocation space. The fix is to use mas_data_end() in mas_skip_node() to detect the nodes data end point and continue walking the tree up until it is safe to move to a node with a higher limit. The walk up the tree also sets the maple state limits so remove the buggy code from mas_skip_node(). Setting the limits had the unfortunate side effect of triggering another bug if the parent node was full and the there was no suitable gap in the second last child, but room in the next child. mas_skip_node() may also be passed a maple state in an error state from mas_anode_descend() when no allocations are available. Return on such an error state immediately. Reported-by: Snild Dolkow <snild@xxxxxxxx> Link: https://lore.kernel.org/linux-mm/cb8dc31a-fef2-1d09-f133-e9f7b9f9e77a@xxxxxxxx/ Cc: <Stable@xxxxxxxxxxxxxxx> Cc: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> Fixes: 54a611b60590 ("Maple Tree: add new data structure") Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> --- lib/maple_tree.c | 24 +++++------------------- 1 file changed, 5 insertions(+), 19 deletions(-) diff --git a/lib/maple_tree.c b/lib/maple_tree.c index 2be86368237d..b1db0bd71aed 100644 --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -5188,35 +5188,21 @@ static inline bool mas_rewind_node(struct ma_state *mas) */ static inline bool mas_skip_node(struct ma_state *mas) { - unsigned char slot, slot_count; - unsigned long *pivots; - enum maple_type mt; + if (mas_is_err(mas)) + return false; - mt = mte_node_type(mas->node); - slot_count = mt_slots[mt] - 1; do { if (mte_is_root(mas->node)) { - slot = mas->offset; - if (slot > slot_count) { + if (mas->offset >= mas_data_end(mas)) { mas_set_err(mas, -EBUSY); return false; } } else { mas_ascend(mas); - slot = mas->offset; - mt = mte_node_type(mas->node); - slot_count = mt_slots[mt] - 1; } - } while (slot > slot_count); - - mas->offset = ++slot; - pivots = ma_pivots(mas_mn(mas), mt); - if (slot > 0) - mas->min = pivots[slot - 1] + 1; - - if (slot <= slot_count) - mas->max = pivots[slot]; + } while (mas->offset >= mas_data_end(mas)); + mas->offset++; return true; } -- 2.39.2
