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authorMichal Hocko <mhocko@suse.cz>2012-01-20 14:33:55 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2012-01-23 08:38:47 -0800
commit687875fb7de4a95223af20ee024282fa9099f860 (patch)
tree1c50d5ac1e31afac82cb8b0a6dd4b1f7bd07eecd /mm
parent6536e3123e5d3371a6f52e32a3d0694bcc987702 (diff)
downloadlinux-stericsson-687875fb7de4a95223af20ee024282fa9099f860.tar.gz
mm: fix NULL ptr dereference in __count_immobile_pages
Fix the following NULL ptr dereference caused by cat /sys/devices/system/memory/memory0/removable Pid: 13979, comm: sed Not tainted 3.0.13-0.5-default #1 IBM BladeCenter LS21 -[7971PAM]-/Server Blade RIP: __count_immobile_pages+0x4/0x100 Process sed (pid: 13979, threadinfo ffff880221c36000, task ffff88022e788480) Call Trace: is_pageblock_removable_nolock+0x34/0x40 is_mem_section_removable+0x74/0xf0 show_mem_removable+0x41/0x70 sysfs_read_file+0xfe/0x1c0 vfs_read+0xc7/0x130 sys_read+0x53/0xa0 system_call_fastpath+0x16/0x1b We are crashing because we are trying to dereference NULL zone which came from pfn=0 (struct page ffffea0000000000). According to the boot log this page is marked reserved: e820 update range: 0000000000000000 - 0000000000010000 (usable) ==> (reserved) and early_node_map confirms that: early_node_map[3] active PFN ranges 1: 0x00000010 -> 0x0000009c 1: 0x00000100 -> 0x000bffa3 1: 0x00100000 -> 0x00240000 The problem is that memory_present works in PAGE_SECTION_MASK aligned blocks so the reserved range sneaks into the the section as well. This also means that free_area_init_node will not take care of those reserved pages and they stay uninitialized. When we try to read the removable status we walk through all available sections and hope that the zone is valid for all pages in the section. But this is not true in this case as the zone and nid are not initialized. We have only one node in this particular case and it is marked as node=1 (rather than 0) and that made the problem visible because page_to_nid will return 0 and there are no zones on the node. Let's check that the zone is valid and that the given pfn falls into its boundaries and mark the section not removable. This might cause some false positives, probably, but we do not have any sane way to find out whether the page is reserved by the platform or it is just not used for whatever other reasons. Signed-off-by: Michal Hocko <mhocko@suse.cz> Acked-by: Mel Gorman <mgorman@suse.de> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: David Rientjes <rientjes@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm')
-rw-r--r--mm/page_alloc.c11
1 files changed, 11 insertions, 0 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 0027d8f4a1bb..21c272d517bc 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5414,6 +5414,17 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count)
bool is_pageblock_removable_nolock(struct page *page)
{
struct zone *zone = page_zone(page);
+ unsigned long pfn = page_to_pfn(page);
+
+ /*
+ * We have to be careful here because we are iterating over memory
+ * sections which are not zone aware so we might end up outside of
+ * the zone but still within the section.
+ */
+ if (!zone || zone->zone_start_pfn > pfn ||
+ zone->zone_start_pfn + zone->spanned_pages <= pfn)
+ return false;
+
return __count_immobile_pages(zone, page, 0);
}