linux-kernel - [PATCH v1 3/3] kernel/resource: cleanup and optimize iomem_is

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Date:   Wed, 11 Aug 2021 22:36:12 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Hanjun Guo <guohanjun@...wei.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        virtualization@...ts.linux-foundation.org, linux-mm@...ck.org
Subject: [PATCH v1 3/3] kernel/resource: cleanup and optimize iomem_is_exclusive()

Let's clean it up a bit, removing the unnecessary usage of r_next() by
next_resource(), and use next_range_resource() in case we are not
interested in a certain subtree.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
 kernel/resource.c | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/kernel/resource.c b/kernel/resource.c
index 2938cf520ca3..ea853a075a83 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1754,9 +1754,8 @@ static int strict_iomem_checks;
  */
 bool iomem_is_exclusive(u64 addr)
 {
-	struct resource *p = &iomem_resource;
+	struct resource *p;
 	bool err = false;
-	loff_t l;
 	int size = PAGE_SIZE;
 
 	if (!strict_iomem_checks)
@@ -1765,27 +1764,31 @@ bool iomem_is_exclusive(u64 addr)
 	addr = addr & PAGE_MASK;
 
 	read_lock(&resource_lock);
-	for (p = p->child; p ; p = r_next(NULL, p, &l)) {
+	for (p = iomem_resource.child; p ;) {
 		/*
 		 * We can probably skip the resources without
 		 * IORESOURCE_IO attribute?
 		 */
 		if (p->start >= addr + size)
 			break;
-		if (p->end < addr)
+		if (p->end < addr) {
+			/* No need to consider children */
+			p = next_resource_skip_children(p);
 			continue;
+		}
+
 		/*
 		 * A resource is exclusive if IORESOURCE_EXCLUSIVE is set
 		 * or CONFIG_IO_STRICT_DEVMEM is enabled and the
 		 * resource is busy.
 		 */
-		if ((p->flags & IORESOURCE_BUSY) == 0)
-			continue;
-		if (IS_ENABLED(CONFIG_IO_STRICT_DEVMEM)
-				|| p->flags & IORESOURCE_EXCLUSIVE) {
+		if (p->flags & IORESOURCE_BUSY &&
+		    (IS_ENABLED(CONFIG_IO_STRICT_DEVMEM) ||
+		     p->flags & IORESOURCE_EXCLUSIVE)) {
 			err = true;
 			break;
 		}
+		p = next_resource(p);
 	}
 	read_unlock(&resource_lock);
 
-- 
2.31.1