[PATCH] printk() should not be called under zone->lock

This patch fixes printk() under zone->lock in show_free_areas().  It can be
unsafe to call printk() under this lock, since caller can try to
allocate/free some memory and selfdeadlock on this lock.  I found
allocations/freeing mem both in netconsole and serial console.

This issue was faced in reallity when meminfo was periodically printed for
debug purposes and netconsole was used.

Signed-off-by: Kirill Korotaev <dev@openvz.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 71a0b2a23f5..423db0db7c0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1491,7 +1491,7 @@ void show_free_areas(void)
         }
 
         for_each_zone(zone) {
-                unsigned long nr, flags, order, total = 0;
+                unsigned long nr[MAX_ORDER], flags, order, total = 0;
 
                 show_node(zone);
                 printk("%s: ", zone->name);
@@ -1502,11 +1502,12 @@ void show_free_areas(void)
 
                 spin_lock_irqsave(&zone->lock, flags);
                 for (order = 0; order < MAX_ORDER; order++) {
-                        nr = zone->free_area[order].nr_free;
-                        total += nr << order;
-                        printk("%lu*%lukB ", nr, K(1UL) << order);
+                        nr[order] = zone->free_area[order].nr_free;
+                        total += nr[order] << order;
                 }
                 spin_unlock_irqrestore(&zone->lock, flags);
+                for (order = 0; order < MAX_ORDER; order++)
+                        printk("%lu*%lukB ", nr[order], K(1UL) << order);
                 printk("= %lukB\n", K(total));
         }