[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>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 71a0b2a..423db0d 100644 (file)
--- 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));
        }