[PATCH] memory hotplug locking: node_size_lock

pgdat->node_size_lock is basically only neeeded in one place in the normal
code: show_mem(), which is the arch-specific sysrq-m printing function.

Strictly speaking, the architectures not doing memory hotplug do no need this
locking in show_mem().  However, they are all included for completeness.  This
should also make any future consolidation of all of the implementations a
little more straightforward.

This lock is also held in the sparsemem code during a memory removal, as
sections are invalidated.  This is the place there pfn_valid() is made false
for a memory area that's being removed.  The lock is only required when doing
pfn_valid() operations on memory which the user does not already have a
reference on the page, such as in show_mem().

Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/arch/alpha/mm/numa.c b/arch/alpha/mm/numa.c
index c7481d59b6df..6d5251254f68 100644
--- a/arch/alpha/mm/numa.c
+++ b/arch/alpha/mm/numa.c
@@ -371,6 +371,8 @@ show_mem(void)
         show_free_areas();
         printk("Free swap:       %6ldkB\n", nr_swap_pages<<(PAGE_SHIFT-10));
         for_each_online_node(nid) {
+                unsigned long flags;
+                pgdat_resize_lock(NODE_DATA(nid), &flags);
                 i = node_spanned_pages(nid);
                 while (i-- > 0) {
                         struct page *page = nid_page_nr(nid, i);
@@ -384,6 +386,7 @@ show_mem(void)
                         else
                                 shared += page_count(page) - 1;
                 }
+                pgdat_resize_unlock(NODE_DATA(nid), &flags);
         }
         printk("%ld pages of RAM\n",total);
         printk("%ld free pages\n",free);