[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, 6 insertions, 1 deletions

diff --git a/arch/ia64/mm/discontig.c b/arch/ia64/mm/discontig.c
index a3788fb84809..a88cdb7232f8 100644
--- a/arch/ia64/mm/discontig.c
+++ b/arch/ia64/mm/discontig.c
@@ -555,9 +555,13 @@ void show_mem(void)
         show_free_areas();
         printk("Free swap:       %6ldkB\n", nr_swap_pages<<(PAGE_SHIFT-10));
         for_each_pgdat(pgdat) {
-                unsigned long present = pgdat->node_present_pages;
+                unsigned long present;
+                unsigned long flags;
                 int shared = 0, cached = 0, reserved = 0;
+
                 printk("Node ID: %d\n", pgdat->node_id);
+                pgdat_resize_lock(pgdat, &flags);
+                present = pgdat->node_present_pages;
                 for(i = 0; i < pgdat->node_spanned_pages; i++) {
                         struct page *page;
                         if (pfn_valid(pgdat->node_start_pfn + i))
@@ -571,6 +575,7 @@ void show_mem(void)
                         else if (page_count(page))
                                 shared += page_count(page)-1;
                 }
+                pgdat_resize_unlock(pgdat, &flags);
                 total_present += present;
                 total_reserved += reserved;
                 total_cached += cached;