[PATCH] perf/HWBP: Optimize __modify_bp_slot() handling

[PATCH] perf/HWBP: Optimize __modify_bp_slot() handling

[Jinchao Wang]

Skip unnecessary release/reserve when old and new types share the same
slot.

Reserve the new slot first, then release the old one to maintain
consistency and avoid transient failures.

Signed-off-by: Jinchao Wang <wangjinchao600@gmail.com>
---
 kernel/events/hw_breakpoint.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/kernel/events/hw_breakpoint.c b/kernel/events/hw_breakpoint.c
index 8ec2cb688903..1cc9cb32ceb4 100644
--- a/kernel/events/hw_breakpoint.c
+++ b/kernel/events/hw_breakpoint.c
@@ -625,23 +625,20 @@ void release_bp_slot(struct perf_event *bp)
 static int __modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
 {
 	int err;
+	enum bp_type_idx old_type_idx, new_type_idx;
 
-	__release_bp_slot(bp, old_type);
+	old_type_idx = find_slot_idx(old_type);
+	new_type_idx = find_slot_idx(new_type);
+	if (old_type_idx == new_type_idx)
+		return 0;
 
 	err = __reserve_bp_slot(bp, new_type);
-	if (err) {
-		/*
-		 * Reserve the old_type slot back in case
-		 * there's no space for the new type.
-		 *
-		 * This must succeed, because we just released
-		 * the old_type slot in the __release_bp_slot
-		 * call above. If not, something is broken.
-		 */
-		WARN_ON(__reserve_bp_slot(bp, old_type));
-	}
+	if (err)
+		return err;
 
-	return err;
+	__release_bp_slot(bp, old_type);
+
+	return 0;
 }
 
 static int modify_bp_slot(struct perf_event *bp, u64 old_type, u64 new_type)
-- 
2.43.0