linux-kernel - [PATCH v5 2/3] kernel/resource: Refactor __request

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Date:   Mon, 19 Apr 2021 17:01:08 +1000
From:   Alistair Popple <apopple@...dia.com>
To:     <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <david@...hat.com>, <daniel.vetter@...ll.ch>,
        <dan.j.williams@...el.com>, <gregkh@...uxfoundation.org>,
        <jhubbard@...dia.com>, <jglisse@...hat.com>,
        <bsingharora@...il.com>, <smuchun@...il.com>,
        Alistair Popple <apopple@...dia.com>
Subject: [PATCH v5 2/3] kernel/resource: Refactor __request_region to allow external locking

Refactor the portion of __request_region() done whilst holding the
resource_lock into a separate function to allow callers to hold the
lock.

Signed-off-by: Alistair Popple <apopple@...dia.com>
---
 kernel/resource.c | 52 +++++++++++++++++++++++++++++------------------
 1 file changed, 32 insertions(+), 20 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index 736768587d2d..75f8da722497 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1181,31 +1181,16 @@ struct address_space *iomem_get_mapping(void)
 	return smp_load_acquire(&iomem_inode)->i_mapping;
 }
 
-/**
- * __request_region - create a new busy resource region
- * @parent: parent resource descriptor
- * @start: resource start address
- * @n: resource region size
- * @name: reserving caller's ID string
- * @flags: IO resource flags
- */
-struct resource * __request_region(struct resource *parent,
+static int __request_region_locked(struct resource *res, struct resource *parent,
 				   resource_size_t start, resource_size_t n,
 				   const char *name, int flags)
 {
 	DECLARE_WAITQUEUE(wait, current);
-	struct resource *res = alloc_resource(GFP_KERNEL);
-	struct resource *orig_parent = parent;
-
-	if (!res)
-		return NULL;
 
 	res->name = name;
 	res->start = start;
 	res->end = start + n - 1;
 
-	write_lock(&resource_lock);
-
 	for (;;) {
 		struct resource *conflict;
 
@@ -1241,13 +1226,40 @@ struct resource * __request_region(struct resource *parent,
 			continue;
 		}
 		/* Uhhuh, that didn't work out.. */
-		free_resource(res);
-		res = NULL;
-		break;
+		return -EBUSY;
 	}
+
+	return 0;
+}
+
+/**
+ * __request_region - create a new busy resource region
+ * @parent: parent resource descriptor
+ * @start: resource start address
+ * @n: resource region size
+ * @name: reserving caller's ID string
+ * @flags: IO resource flags
+ */
+struct resource *__request_region(struct resource *parent,
+				  resource_size_t start, resource_size_t n,
+				  const char *name, int flags)
+{
+	struct resource *res = alloc_resource(GFP_KERNEL);
+	int ret;
+
+	if (!res)
+		return NULL;
+
+	write_lock(&resource_lock);
+	ret = __request_region_locked(res, parent, start, n, name, flags);
 	write_unlock(&resource_lock);
 
-	if (res && orig_parent == &iomem_resource)
+	if (ret) {
+		free_resource(res);
+		return NULL;
+	}
+
+	if (parent == &iomem_resource)
 		revoke_iomem(res);
 
 	return res;
-- 
2.20.1