[PATCH] printk() should not be called under zone->lock (8f9de51a) · Commits · 戴 / test

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>

mm/page_alloc.c

+5 −4

Original line number	Diff line number	Diff line
		@@ -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));
		}

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