From: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> commit 0fa99fdfe1b38da396d0b2d1496a823bcd0ebea0 upstream. Patch series "Fix mas_skip_node() for mas_empty_area()", v2. mas_empty_area() was incorrectly returning an error when there was room. The issue was tracked down to mas_skip_node() using the incorrect end-of-slot count. Instead of using the nodes hard limit, the limit of data should be used. mas_skip_node() was also setting the min and max to that of the child node, which was unnecessary. Within these limits being set, there was also a bug that corrupted the maple state's max if the offset was set to the maximum node pivot. The bug was without consequence unless there was a sufficient gap in the next child node which would cause an error to be returned. This patch set fixes these errors by removing the limit setting from mas_skip_node() and uses the mas_data_end() for slot limits, and adds tests for all failures discovered. This patch (of 2): 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. Link: https://lkml.kernel.org/r/20230307180247.2220303-1-Liam.Howlett@xxxxxxxxxx Link: https://lkml.kernel.org/r/20230307180247.2220303-2-Liam.Howlett@xxxxxxxxxx Fixes: 54a611b60590 ("Maple Tree: add new data structure") Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> Reported-by: Snild Dolkow <snild@xxxxxxxx> Link: https://lore.kernel.org/linux-mm/cb8dc31a-fef2-1d09-f133-e9f7b9f9e77a@xxxxxxxx/ Tested-by: Snild Dolkow <snild@xxxxxxxx> Cc: Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- lib/maple_tree.c | 24 +++++------------------- 1 file changed, 5 insertions(+), 19 deletions(-) --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -5088,35 +5088,21 @@ static inline bool mas_rewind_node(struc */ 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; }
