path: root/mm/rmap.c
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authorMel Gorman <mel@csn.ul.ie>2010-05-24 14:32:24 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-25 08:06:59 -0700
commita8bef8ff6ea15fa4c67433cab0f5f3484574ef7c (patch)
tree3ea9c122e02f523379d4560ee2134124d097895c /mm/rmap.c
parente9e96b39f932a065e14f5d5bab0797ae261d03b5 (diff)
mm: migration: avoid race between shift_arg_pages() and rmap_walk() during migration by not migrating temporary stacks
Page migration requires rmap to be able to find all ptes mapping a page at all times, otherwise the migration entry can be instantiated, but it is possible to leave one behind if the second rmap_walk fails to find the page. If this page is later faulted, migration_entry_to_page() will call BUG because the page is locked indicating the page was migrated by the migration PTE not cleaned up. For example kernel BUG at include/linux/swapops.h:105! invalid opcode: 0000 [#1] PREEMPT SMP ... Call Trace: [<ffffffff810e951a>] handle_mm_fault+0x3f8/0x76a [<ffffffff8130c7a2>] do_page_fault+0x44a/0x46e [<ffffffff813099b5>] page_fault+0x25/0x30 [<ffffffff8114de33>] load_elf_binary+0x152a/0x192b [<ffffffff8111329b>] search_binary_handler+0x173/0x313 [<ffffffff81114896>] do_execve+0x219/0x30a [<ffffffff8100a5c6>] sys_execve+0x43/0x5e [<ffffffff8100320a>] stub_execve+0x6a/0xc0 RIP [<ffffffff811094ff>] migration_entry_wait+0xc1/0x129 There is a race between shift_arg_pages and migration that triggers this bug. A temporary stack is setup during exec and later moved. If migration moves a page in the temporary stack and the VMA is then removed before migration completes, the migration PTE may not be found leading to a BUG when the stack is faulted. This patch causes pages within the temporary stack during exec to be skipped by migration. It does this by marking the VMA covering the temporary stack with an otherwise impossible combination of VMA flags. These flags are cleared when the temporary stack is moved to its final location. [kamezawa.hiroyu@jp.fujitsu.com: idea for having migration skip temporary stacks] Signed-off-by: Mel Gorman <mel@csn.ul.ie> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Reviewed-by: Rik van Riel <riel@redhat.com> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Minchan Kim <minchan.kim@gmail.com> Cc: Christoph Lameter <cl@linux.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Rik van Riel <riel@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/rmap.c')
1 files changed, 29 insertions, 1 deletions
diff --git a/mm/rmap.c b/mm/rmap.c
index b5c320f7d0a5..38a336e2eea1 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1131,6 +1131,20 @@ static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
return ret;
+static bool is_vma_temporary_stack(struct vm_area_struct *vma)
+ int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
+ if (!maybe_stack)
+ return false;
+ if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
+ return true;
+ return false;
* try_to_unmap_anon - unmap or unlock anonymous page using the object-based
* rmap method
@@ -1159,7 +1173,21 @@ static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
struct vm_area_struct *vma = avc->vma;
- unsigned long address = vma_address(page, vma);
+ unsigned long address;
+ /*
+ * During exec, a temporary VMA is setup and later moved.
+ * The VMA is moved under the anon_vma lock but not the
+ * page tables leading to a race where migration cannot
+ * find the migration ptes. Rather than increasing the
+ * locking requirements of exec(), migration skips
+ * temporary VMAs until after exec() completes.
+ */
+ if (PAGE_MIGRATION && (flags & TTU_MIGRATION) &&
+ is_vma_temporary_stack(vma))
+ continue;
+ address = vma_address(page, vma);
if (address == -EFAULT)
ret = try_to_unmap_one(page, vma, address, flags);

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