Re: [PATCH v1 3/3] kernel/resource: cleanup and optimize iomem_is_exclusive()

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On Wednesday, August 11, 2021, David Hildenbrand <david@xxxxxxxxxx> wrote:
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@xxxxxxxxxx>
---
 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 ;) {

I consider the ordinal part of p initialization is slightly better and done outside of read lock.

Something like
p= &iomem_res...;
read lock
for (p = p->child; ...) {

 
                /*
                 * 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



--
With Best Regards,
Andy Shevchenko


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