On 12.08.21 09:14, Andy Shevchenko wrote:

On Thursday, August 12, 2021, David Hildenbrand <david@redhat.com 
<mailto:david@redhat.com>> wrote:

    On 11.08.21 22:47, Andy Shevchenko wrote:



        On Wednesday, August 11, 2021, David Hildenbrand
        <david@redhat.com <mailto:david@redhat.com>
        <mailto:david@redhat.com <mailto:david@redhat.com>>> 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@redhat.com
        <mailto:david@redhat.com>
             <mailto:david@redhat.com <mailto:david@redhat.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 ;) {


    Hi Andy,


        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; ...) {


    Why should we care about doing that outside of the lock? That smells
    like a micro-optimization the compiler will most probably overwrite
    either way as the address of iomem_resource is just constant?

    Also, for me it's much more readable and compact if we perform a
    single initialization instead of two separate ones in this case.

    We're using the pattern I use in, find_next_iomem_res() and
    __region_intersects(), while we use the old pattern in
    iomem_map_sanity_check(), where we also use the same unnecessary
    r_next() call.

    I might just cleanup iomem_map_sanity_check() in a similar way.



Yes, it’s like micro optimization. If you want your way I suggest then 
to add a macro

#define for_each_iomem_resource_child() \
  for (iomem_resource...)

I think the only thing that really makes sense would be something like this on top (not compiled yet):

diff --git a/kernel/resource.c b/kernel/resource.c
index ea853a075a83..35aaa72df0ce 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c

@@ -80,6 +80,11 @@ static struct resource *next_resource_skip_children(struct resource *p)
         return p->sibling;
  }
  
+#define for_each_resource(_root, _p, _skip_children) \
+       for ((_p) = (_root)->child; (_p); \
+            (_p) = (_skip_children) ? next_resource_skip_children(_p) : \
+                                      next_resource(_p))
+
  static void *r_next(struct seq_file *m, void *v, loff_t *pos)
  {
         struct resource *p = v;

@@ -1714,16 +1719,16 @@ int iomem_map_sanity_check(resource_size_t addr, unsigned long size)
  bool iomem_range_contains_excluded(u64 addr, u64 size)
  {
         const unsigned int flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_EXCLUSIVE;
-       bool excluded = false;
+       bool skip_children, excluded = false;
         struct resource *p;
  
         read_lock(&resource_lock);
-       for (p = iomem_resource.child; p ;) {
+       for_each_resource(&iomem_resource, p, skip_children) {
                 if (p->start >= addr + size)
                         break;
                 if (p->end < addr) {
                         /* No need to consider children */
-                       p = next_resource_skip_children(p);
+                       skip_children = true;
                         continue;
                 }
                 /*

@@ -1735,7 +1740,7 @@ bool iomem_range_contains_excluded(u64 addr, u64 size)
                         excluded = true;
                         break;
                 }
-               p = next_resource(p);
+               skip_children = false;
         }
         read_unlock(&resource_lock);
  

@@ -1755,7 +1760,7 @@ static int strict_iomem_checks;
  bool iomem_is_exclusive(u64 addr)
  {
         struct resource *p;
-       bool err = false;
+       bool skip_children, err = false;
         int size = PAGE_SIZE;
  
         if (!strict_iomem_checks)

@@ -1764,7 +1769,7 @@ bool iomem_is_exclusive(u64 addr)
         addr = addr & PAGE_MASK;
  
         read_lock(&resource_lock);
-       for (p = iomem_resource.child; p ;) {
+       for_each_resource(&iomem_resource, p, skip_children) {
                 /*
                  * We can probably skip the resources without
                  * IORESOURCE_IO attribute?

@@ -1773,7 +1778,7 @@ bool iomem_is_exclusive(u64 addr)
                         break;
                 if (p->end < addr) {
                         /* No need to consider children */
-                       p = next_resource_skip_children(p);
+                       skip_children = true;
                         continue;
                 }
  

@@ -1788,7 +1793,7 @@ bool iomem_is_exclusive(u64 addr)
                         err = true;
                         break;
                 }
-               p = next_resource(p);
+               skip_children = false;
         }
         read_unlock(&resource_lock);
  

Thoughts?


-- 
Thanks,

David / dhildenb