[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/parisc/mm/init.c b/arch/parisc/mm/init.c
index 2886ad70db48..29b998e430e6 100644
--- a/arch/parisc/mm/init.c
+++ b/arch/parisc/mm/init.c
@@ -505,7 +505,9 @@ void show_mem(void)
 
                 for (j = node_start_pfn(i); j < node_end_pfn(i); j++) {
                         struct page *p;
+                        unsigned long flags;
 
+                        pgdat_resize_lock(NODE_DATA(i), &flags);
                         p = nid_page_nr(i, j) - node_start_pfn(i);
 
                         total++;
@@ -517,6 +519,7 @@ void show_mem(void)
                                 free++;
                         else
                                 shared += page_count(p) - 1;
+                        pgdat_resize_unlock(NODE_DATA(i), &flags);
                 }
         }
 #endif