Re: [PATCH] maple_tree: Fix mas_prev() state separation code

On Thu, Dec 07, 2023 at 02:33:19PM -0500, Liam R. Howlett wrote:

mas_prev() was setting the ma_underflow condition when the limit was reached and not when the limit was attempting to go lower. This resulted in the incorrect behaviour on subsequent actions.

This commit fixes the status setting to only set ma_underflow when the lower limit is attempted to be decremented, and modifies the testing to ensure that's the case.

Signed-off-by: Liam R. Howlett Liam.Howlett@oracle.com

Is this is related to the report[1] I forwarded? If so, please add these tags too:

Reported-by: Linux Kernel Functional Testing lkft@linaro.org Closes: https://lore.kernel.org/all/CA+G9fYs-j2FYZSFSVZj48mgoM9gQd4-7M2mu2Ez3D1DqDdW... [1]

Thanks either way!

-Kees

---

Andrew,

This should be clean to squash into 7f79fdb1d94d7 ("maple_tree: separate ma_state node from status.") which is currently in your mm-unstable branch.

Thanks, Liam

lib/maple_tree.c | 16 ++++++++++++---- lib/test_maple_tree.c | 9 +++++++-- 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c index 89f8d21602774..47f2a7a973852 100644 --- a/lib/maple_tree.c +++ b/lib/maple_tree.c @@ -4432,6 +4432,9 @@ static void *mas_prev_slot(struct ma_state *mas, unsigned long min, bool empty) mas->last = mas->index - 1; mas->index = mas_safe_min(mas, pivots, mas->offset); } else {

• if (mas->index <= min)
  

• 	goto underflow;
  

• if (mas_prev_node(mas, min)) { mas_rewalk(mas, save_point); goto retry;

@@ -4452,15 +4455,15 @@ static void *mas_prev_slot(struct ma_state *mas, unsigned long min, bool empty) if (unlikely(mas_rewalk_if_dead(mas, node, save_point))) goto retry;

• if (mas->index <= min)

• mas->status = ma_underflow;
  

if (likely(entry)) return entry; if (!empty) {

• if (mas_is_underflow(mas))
  

• if (mas->index <= min) {
  

• 	mas->status = ma_underflow;
  return NULL;
  

• }
  

goto again; } @@ -4596,7 +4599,7 @@ static void *mas_next_slot(struct ma_state *mas, unsigned long max, bool empty) if (unlikely(mas_rewalk_if_dead(mas, node, save_point))) goto retry;

• if (pivot >= max) {
  

• if (pivot >= max) { /* Was at the limit, next will extend beyond */
  mas->status = ma_overflow;
  return NULL;
  

  }

@@ -4611,6 +4614,11 @@ static void *mas_next_slot(struct ma_state *mas, unsigned long max, bool empty) else mas->last = mas->max; } else {

• if (mas->last >= max) {
  

• 	mas->status = ma_overflow;
  

• 	return NULL;
  

• }
  

• if (mas_next_node(mas, node, max)) { mas_rewalk(mas, save_point); goto retry;

diff --git a/lib/test_maple_tree.c b/lib/test_maple_tree.c index 15fbeb788f3ac..29185ac5c727f 100644 --- a/lib/test_maple_tree.c +++ b/lib/test_maple_tree.c @@ -3294,8 +3294,8 @@ static noinline void __init check_state_handling(struct maple_tree *mt) MT_BUG_ON(mt, mas.last != 0x1500); MT_BUG_ON(mt, !mas_is_active(&mas));

• /* next:active ->active */
• entry = mas_next(&mas, ULONG_MAX);

• /* next:active ->active (spanning limit) */
• entry = mas_next(&mas, 0x2100); MT_BUG_ON(mt, entry != ptr2); MT_BUG_ON(mt, mas.index != 0x2000); MT_BUG_ON(mt, mas.last != 0x2500);

@@ -3360,6 +3360,11 @@ static noinline void __init check_state_handling(struct maple_tree *mt) 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_is_active(&mas)); /* spanning limit */
• entry = mas_prev(&mas, 0x1200); /* underflow */
• 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_is_underflow(&mas));

/* prev:underflow -> underflow (lower limit) spanning end range */ -- 2.40.1