Re: [PATCH 25/34] maple_tree: Clear up index and last setting in single entry tree

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在 2023/4/25 22:09, Liam R. Howlett 写道:
When there is a single entry tree (range of 0-0 pointing to an entry),
then ensure the limit is either 0-0 or 1-oo, depending on where the user
walks.  Ensure the correct node setting as well; either MAS_ROOT or
MAS_NONE.

Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
---
  lib/maple_tree.c | 21 +++++++++++----------
  1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 20f0a10dc5608..31cbfd7b44728 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -5099,24 +5099,25 @@ void *mas_walk(struct ma_state *mas)
  {
  	void *entry;
+ if (mas_is_none(mas) || mas_is_paused(mas))
+		mas->node = MAS_START;
  retry:
  	entry = mas_state_walk(mas);
-	if (mas_is_start(mas))
+	if (mas_is_start(mas)) {
  		goto retry;
-
-	if (mas_is_ptr(mas)) {
+	} else if (mas_is_none(mas)) {
+		mas->index = 0;
+		mas->last = ULONG_MAX;
+	} else if (mas_is_ptr(mas)) {
  		if (!mas->index) {
  			mas->last = 0;
-		} else {
-			mas->index = 1;
-			mas->last = ULONG_MAX;
+			return mas_root(mas);
Why we call mas_root() to get the single entry stored in root again?
I think it's not safe. In RCU mode, if someone modify the tree to a normal tree(not a single entry tree), mas_root() will return a address.
So, this may cause a race bug. We can return entry directly.
  		}
-		return entry;
-	}
- if (mas_is_none(mas)) {
-		mas->index = 0;
+		mas->index = 1;
  		mas->last = ULONG_MAX;
+		mas->node = MAS_NONE;
+		return NULL;
  	}
return entry;




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