linux-kernel - [PATCH 2/2] maple_tree: add a fast path case in mas_wr_slot

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20230602075353.5917-2-zhangpeng.00@bytedance.com>
Date:   Fri,  2 Jun 2023 15:53:53 +0800
From:   Peng Zhang <zhangpeng.00@...edance.com>
To:     Liam.Howlett@...cle.com
Cc:     akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, maple-tree@...ts.infradead.org,
        Peng Zhang <zhangpeng.00@...edance.com>
Subject: [PATCH 2/2] maple_tree: add a fast path case in mas_wr_slot_store()

When the new range overwrites three ranges and does not touch the
boundaries on both sides, the number of entries will not be increased,
so we can just update the pivots as a fast path. However, it may
introduce potential risks in RCU mode (although it can pass the test),
because it updates two pivots. We only enable it in non-RCU mode for now.

Signed-off-by: Peng Zhang <zhangpeng.00@...edance.com>
---
 lib/maple_tree.c | 33 +++++++++++++++++++++------------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index cfd9fad308a2..ec82441ca3e8 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -4100,23 +4100,32 @@ static inline bool mas_wr_slot_store(struct ma_wr_state *wr_mas)
 {
 	struct ma_state *mas = wr_mas->mas;
 	unsigned char offset = mas->offset;
+	void __rcu **slots = wr_mas->slots;
 	bool gap = false;
 
-	if (wr_mas->offset_end - offset != 1)
-		return false;
-
-	gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset);
-	gap |= !mt_slot_locked(mas->tree, wr_mas->slots, offset + 1);
+	gap |= !mt_slot_locked(mas->tree, slots, offset);
+	gap |= !mt_slot_locked(mas->tree, slots, offset + 1);
 
-	if (mas->index == wr_mas->r_min) {
-		/* Overwriting the range and over a part of the next range. */
-		rcu_assign_pointer(wr_mas->slots[offset], wr_mas->entry);
-		wr_mas->pivots[offset] = mas->last;
-	} else {
-		/* Overwriting a part of the range and over the next range */
-		rcu_assign_pointer(wr_mas->slots[offset + 1], wr_mas->entry);
+	if (wr_mas->offset_end - offset == 1) {
+		if (mas->index == wr_mas->r_min) {
+			/* Overwriting the range and a part of the next one */
+			rcu_assign_pointer(slots[offset], wr_mas->entry);
+			wr_mas->pivots[offset] = mas->last;
+		} else {
+			/* Overwriting a part of the range and the next one */
+			rcu_assign_pointer(slots[offset + 1], wr_mas->entry);
+			wr_mas->pivots[offset] = mas->index - 1;
+			mas->offset++; /* Keep mas accurate. */
+		}
+	} else if (!mt_in_rcu(mas->tree)) {
+		/* Overwriting three ranges, but don't touch the boundaries */
+		gap |= !mt_slot_locked(mas->tree, slots, offset + 2);
+		rcu_assign_pointer(slots[offset + 1], wr_mas->entry);
 		wr_mas->pivots[offset] = mas->index - 1;
+		wr_mas->pivots[offset + 1] = mas->last;
 		mas->offset++; /* Keep mas accurate. */
+	} else {
+		return false;
 	}
 
 	trace_ma_write(__func__, mas, 0, wr_mas->entry);
-- 
2.20.1