From 1cdde0d32e34c5849aa647d0a3a017406e47ff84 Mon Sep 17 00:00:00 2001
From: Max Wash <mbswash@gmail.com>
Date: Thu, 26 Feb 2026 19:38:49 +0000
Subject: [PATCH] kernel: add functions for safely (un)locking pairs of objects

when locking a pair of objects, the object with the lesser memory address
is always locked first. the pair is unlocked in the opposite order.
---
 include/kernel/object.h | 23 +++++++++++++++++++++++
 kernel/object.c         | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/include/kernel/object.h b/include/kernel/object.h
index 686ab2e..55db392 100644
--- a/include/kernel/object.h
+++ b/include/kernel/object.h
@@ -31,6 +31,20 @@ extern "C" {
 		unsigned long flags)                                           \
 	{                                                                      \
 		object_unlock_irqrestore(&p->base, flags);                     \
+	}                                                                      \
+	static inline void object_name##_lock_pair_irqsave(                    \
+		struct object_name *a,                                         \
+		struct object_name *b,                                         \
+		unsigned long *flags)                                          \
+	{                                                                      \
+		object_lock_pair_irqsave(&a->base, &b->base, flags);           \
+	}                                                                      \
+	static inline void object_name##_unlock_pair_irqrestore(               \
+		struct object_name *a,                                         \
+		struct object_name *b,                                         \
+		unsigned long flags)                                           \
+	{                                                                      \
+		object_unlock_pair_irqrestore(&a->base, &b->base, flags);      \
 	}
 
 #define OBJECT_MAGIC    0xBADDCAFE
@@ -92,6 +106,15 @@ extern void object_unlock(struct object *obj);
 extern void object_lock_irqsave(struct object *obj, unsigned long *flags);
 extern void object_unlock_irqrestore(struct object *obj, unsigned long flags);
 
+extern void object_lock_pair_irqsave(
+	struct object *a,
+	struct object *b,
+	unsigned long *flags);
+extern void object_unlock_pair_irqrestore(
+	struct object *a,
+	struct object *b,
+	unsigned long flags);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/kernel/object.c b/kernel/object.c
index abcd84b..c05339d 100644
--- a/kernel/object.c
+++ b/kernel/object.c
@@ -178,6 +178,38 @@ void object_unlock_irqrestore(struct object *obj, unsigned long flags)
 	spin_unlock_irqrestore(&obj->ob_lock, flags);
 }
 
+void object_lock_pair_irqsave(
+	struct object *a,
+	struct object *b,
+	unsigned long *flags)
+{
+	if (a == b) {
+		object_lock_irqsave(a, flags);
+	} else if (a < b) {
+		object_lock_irqsave(a, flags);
+		object_lock(b);
+	} else {
+		object_lock_irqsave(b, flags);
+		object_lock(a);
+	}
+}
+
+void object_unlock_pair_irqrestore(
+	struct object *a,
+	struct object *b,
+	unsigned long flags)
+{
+	if (a == b) {
+		object_unlock_irqrestore(a, flags);
+	} else if (a < b) {
+		object_unlock(b);
+		object_unlock_irqrestore(a, flags);
+	} else {
+		object_unlock(a);
+		object_unlock_irqrestore(b, flags);
+	}
+}
+
 void *object_data(struct object *obj)
 {
 	return (char *)obj + sizeof *obj;