maple_tree: add MAS_UNDERFLOW and MAS_OVERFLOW states

When updating the maple tree iterator to avoid rewalks, an issue was
introduced when shifting beyond the limits.  This can be seen by trying to
go to the previous address of 0, which would set the maple node to
MAS_NONE and keep the range as the last entry.

Subsequent calls to mas_find() would then search upwards from mas->last
and skip the value at mas->index/mas->last.  This showed up as a bug in
mprotect which skips the actual VMA at the current range after attempting
to go to the previous VMA from 0.

Since MAS_NONE may already be set when searching for a value that isn't
contained within a node, changing the handling of MAS_NONE in mas_find()
would make the code more complicated and error prone.  Furthermore, there
was no way to tell which limit was hit, and thus which action to take
(next or the entry at the current range).

This solution is to add two states to track what happened with the
previous iterator action.  This allows for the expected behaviour of the
next command to return the correct item (either the item at the range
requested, or the next/previous).

Tests are also added and updated accordingly.

Link: https://lkml.kernel.org/r/20230921181236.509072-3-Liam.Howlett@oracle.com
Link: https://gist.github.com/heatd/85d2971fae1501b55b6ea401fbbe485b
Link: https://lore.kernel.org/linux-mm/20230921181236.509072-1-Liam.Howlett@oracle.com/
Fixes: 39193685d585 ("maple_tree: try harder to keep active node with mas_prev()")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reported-by: Pedro Falcato <pedro.falcato@gmail.com>
Closes: https://gist.github.com/heatd/85d2971fae1501b55b6ea401fbbe485b
Closes: https://bugs.archlinux.org/task/79656
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 72 insertions, 15 deletions

diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c
index 0674aebd4423..06959165e2f9 100644
--- a/lib/test_maple_tree.c
+++ b/lib/test_maple_tree.c
@@ -2166,7 +2166,7 @@ static noinline void __init next_prev_test(struct maple_tree *mt)
 	MT_BUG_ON(mt, val != NULL);
 	MT_BUG_ON(mt, mas.index != 0);
 	MT_BUG_ON(mt, mas.last != 5);
-	MT_BUG_ON(mt, mas.node != MAS_NONE);
+	MT_BUG_ON(mt, mas.node != MAS_UNDERFLOW);
 
 	mas.index = 0;
 	mas.last = 5;
@@ -2917,6 +2917,7 @@ static noinline void __init check_empty_area_fill(struct maple_tree *mt)
  *		exists	MAS_NONE	active		range
  *		exists	active		active		range
  *		DNE	active		active		set to last range
+ *		ERANGE	active		MAS_OVERFLOW	last range
  *
  * Function	ENTRY	Start		Result		index & last
  * mas_prev()
@@ -2945,6 +2946,7 @@ static noinline void __init check_empty_area_fill(struct maple_tree *mt)
  *		any	MAS_ROOT	MAS_NONE	0
  *		exists	active		active		range
  *		DNE	active		active		last range
+ *		ERANGE	active		MAS_UNDERFLOW	last range
  *
  * Function	ENTRY	Start		Result		index & last
  * mas_find()
@@ -2955,7 +2957,7 @@ static noinline void __init check_empty_area_fill(struct maple_tree *mt)
  *		DNE	MAS_START	MAS_NONE	0
  *		DNE	MAS_PAUSE	MAS_NONE	0
  *		DNE	MAS_ROOT	MAS_NONE	0
- *		DNE	MAS_NONE	MAS_NONE	0
+ *		DNE	MAS_NONE	MAS_NONE	1
  *				if index ==  0
  *		exists	MAS_START	MAS_ROOT	0
  *		exists	MAS_PAUSE	MAS_ROOT	0
@@ -2967,7 +2969,7 @@ static noinline void __init check_empty_area_fill(struct maple_tree *mt)
  *		DNE	MAS_START	active		set to max
  *		exists	MAS_PAUSE	active		range
  *		DNE	MAS_PAUSE	active		set to max
- *		exists	MAS_NONE	active		range
+ *		exists	MAS_NONE	active		range (start at last)
  *		exists	active		active		range
  *		DNE	active		active		last range (max < last)
  *
@@ -2992,7 +2994,7 @@ static noinline void __init check_empty_area_fill(struct maple_tree *mt)
  *		DNE	MAS_START	active		set to min
  *		exists	MAS_PAUSE	active		range
  *		DNE	MAS_PAUSE	active		set to min
- *		exists	MAS_NONE	active		range
+ *		exists	MAS_NONE	active		range (start at index)
  *		exists	active		active		range
  *		DNE	active		active		last range (min > index)
  *
@@ -3039,10 +3041,10 @@ static noinline void __init check_state_handling(struct maple_tree *mt)
 	mtree_store_range(mt, 0, 0, ptr, GFP_KERNEL);
 
 	mas_lock(&mas);
-	/* prev: Start -> none */
+	/* prev: Start -> underflow*/
 	entry = mas_prev(&mas, 0);
 	MT_BUG_ON(mt, entry != NULL);
-	MT_BUG_ON(mt, mas.node != MAS_NONE);
+	MT_BUG_ON(mt, mas.node != MAS_UNDERFLOW);
 
 	/* prev: Start -> root */
 	mas_set(&mas, 10);
@@ -3069,7 +3071,7 @@ static noinline void __init check_state_handling(struct maple_tree *mt)
 	MT_BUG_ON(mt, entry != NULL);
 	MT_BUG_ON(mt, mas.node != MAS_NONE);
 
-	/* next: start -> none */
+	/* next: start -> none*/
 	mas_set(&mas, 10);
 	entry = mas_next(&mas, ULONG_MAX);
 	MT_BUG_ON(mt, mas.index != 1);
@@ -3268,25 +3270,46 @@ static noinline void __init check_state_handling(struct maple_tree *mt)
 	MT_BUG_ON(mt, mas.last != 0x2500);
 	MT_BUG_ON(mt, !mas_active(mas));
 
-	/* next:active -> active out of range*/
+	/* next:active -> active beyond data */
 	entry = mas_next(&mas, 0x2999);
 	MT_BUG_ON(mt, entry != NULL);
 	MT_BUG_ON(mt, mas.index != 0x2501);
 	MT_BUG_ON(mt, mas.last != 0x2fff);
 	MT_BUG_ON(mt, !mas_active(mas));
 
-	/* Continue after out of range*/
+	/* Continue after last range ends after max */
 	entry = mas_next(&mas, ULONG_MAX);
 	MT_BUG_ON(mt, entry != ptr3);
 	MT_BUG_ON(mt, mas.index != 0x3000);
 	MT_BUG_ON(mt, mas.last != 0x3500);
 	MT_BUG_ON(mt, !mas_active(mas));
 
-	/* next:active -> active out of range*/
+	/* next:active -> active continued */
+	entry = mas_next(&mas, ULONG_MAX);
+	MT_BUG_ON(mt, entry != NULL);
+	MT_BUG_ON(mt, mas.index != 0x3501);
+	MT_BUG_ON(mt, mas.last != ULONG_MAX);
+	MT_BUG_ON(mt, !mas_active(mas));
+
+	/* next:active -> overflow  */
 	entry = mas_next(&mas, ULONG_MAX);
 	MT_BUG_ON(mt, entry != NULL);
 	MT_BUG_ON(mt, mas.index != 0x3501);
 	MT_BUG_ON(mt, mas.last != ULONG_MAX);
+	MT_BUG_ON(mt, mas.node != MAS_OVERFLOW);
+
+	/* next:overflow -> overflow  */
+	entry = mas_next(&mas, ULONG_MAX);
+	MT_BUG_ON(mt, entry != NULL);
+	MT_BUG_ON(mt, mas.index != 0x3501);
+	MT_BUG_ON(mt, mas.last != ULONG_MAX);
+	MT_BUG_ON(mt, mas.node != MAS_OVERFLOW);
+
+	/* prev:overflow -> active  */
+	entry = mas_prev(&mas, 0);
+	MT_BUG_ON(mt, entry != ptr3);
+	MT_BUG_ON(mt, mas.index != 0x3000);
+	MT_BUG_ON(mt, mas.last != 0x3500);
 	MT_BUG_ON(mt, !mas_active(mas));
 
 	/* next: none -> active, skip value at location */
@@ -3307,11 +3330,46 @@ static noinline void __init check_state_handling(struct maple_tree *mt)
 	MT_BUG_ON(mt, mas.last != 0x1500);
 	MT_BUG_ON(mt, !mas_active(mas));
 
-	/* prev:active -> active out of range*/
+	/* prev:active -> active spanning end range */
+	entry = mas_prev(&mas, 0x0100);
+	MT_BUG_ON(mt, entry != NULL);
+	MT_BUG_ON(mt, mas.index != 0);
+	MT_BUG_ON(mt, mas.last != 0x0FFF);
+	MT_BUG_ON(mt, !mas_active(mas));
+
+	/* prev:active -> underflow */
+	entry = mas_prev(&mas, 0);
+	MT_BUG_ON(mt, entry != NULL);
+	MT_BUG_ON(mt, mas.index != 0);
+	MT_BUG_ON(mt, mas.last != 0x0FFF);
+	MT_BUG_ON(mt, mas.node != MAS_UNDERFLOW);
+
+	/* prev:underflow -> underflow */
 	entry = mas_prev(&mas, 0);
 	MT_BUG_ON(mt, entry != NULL);
 	MT_BUG_ON(mt, mas.index != 0);
 	MT_BUG_ON(mt, mas.last != 0x0FFF);
+	MT_BUG_ON(mt, mas.node != MAS_UNDERFLOW);
+
+	/* next:underflow -> active */
+	entry = mas_next(&mas, ULONG_MAX);
+	MT_BUG_ON(mt, entry != ptr);
+	MT_BUG_ON(mt, mas.index != 0x1000);
+	MT_BUG_ON(mt, mas.last != 0x1500);
+	MT_BUG_ON(mt, !mas_active(mas));
+
+	/* prev:first value -> underflow */
+	entry = mas_prev(&mas, 0x1000);
+	MT_BUG_ON(mt, entry != NULL);
+	MT_BUG_ON(mt, mas.index != 0x1000);
+	MT_BUG_ON(mt, mas.last != 0x1500);
+	MT_BUG_ON(mt, mas.node != MAS_UNDERFLOW);
+
+	/* find:underflow -> first value */
+	entry = mas_find(&mas, ULONG_MAX);
+	MT_BUG_ON(mt, entry != ptr);
+	MT_BUG_ON(mt, mas.index != 0x1000);
+	MT_BUG_ON(mt, mas.last != 0x1500);
 	MT_BUG_ON(mt, !mas_active(mas));
 
 	/* prev: pause ->active */
@@ -3325,14 +3383,14 @@ static noinline void __init check_state_handling(struct maple_tree *mt)
 	MT_BUG_ON(mt, mas.last != 0x2500);
 	MT_BUG_ON(mt, !mas_active(mas));
 
-	/* prev:active -> active out of range*/
+	/* prev:active -> active spanning min */
 	entry = mas_prev(&mas, 0x1600);
 	MT_BUG_ON(mt, entry != NULL);
 	MT_BUG_ON(mt, mas.index != 0x1501);
 	MT_BUG_ON(mt, mas.last != 0x1FFF);
 	MT_BUG_ON(mt, !mas_active(mas));
 
-	/* prev: active ->active, continue*/
+	/* prev: active ->active, continue */
 	entry = mas_prev(&mas, 0);
 	MT_BUG_ON(mt, entry != ptr);
 	MT_BUG_ON(mt, mas.index != 0x1000);
@@ -3379,7 +3437,7 @@ static noinline void __init check_state_handling(struct maple_tree *mt)
 	MT_BUG_ON(mt, mas.last != 0x2FFF);
 	MT_BUG_ON(mt, !mas_active(mas));
 
-	/* find: none ->active */
+	/* find: overflow ->active */
 	entry = mas_find(&mas, 0x5000);
 	MT_BUG_ON(mt, entry != ptr3);
 	MT_BUG_ON(mt, mas.index != 0x3000);
@@ -3778,7 +3836,6 @@ static int __init maple_tree_seed(void)
 	check_empty_area_fill(&tree);
 	mtree_destroy(&tree);
 
-
 	mt_init_flags(&tree, MT_FLAGS_ALLOC_RANGE);
 	check_state_handling(&tree);
 	mtree_destroy(&tree);