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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 /fs/exec.c
parente9e96b39f932a065e14f5d5bab0797ae261d03b5 (diff)
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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 'fs/exec.c')
-rw-r--r--fs/exec.c7
1 files changed, 6 insertions, 1 deletions
diff --git a/fs/exec.c b/fs/exec.c
index e6e94c626c2..9badbc0bfb1 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -242,9 +242,10 @@ static int __bprm_mm_init(struct linux_binprm *bprm)
* use STACK_TOP because that can depend on attributes which aren't
* configured yet.
*/
+ BUG_ON(VM_STACK_FLAGS & VM_STACK_INCOMPLETE_SETUP);
vma->vm_end = STACK_TOP_MAX;
vma->vm_start = vma->vm_end - PAGE_SIZE;
- vma->vm_flags = VM_STACK_FLAGS;
+ vma->vm_flags = VM_STACK_FLAGS | VM_STACK_INCOMPLETE_SETUP;
vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
INIT_LIST_HEAD(&vma->anon_vma_chain);
err = insert_vm_struct(mm, vma);
@@ -616,6 +617,7 @@ int setup_arg_pages(struct linux_binprm *bprm,
else if (executable_stack == EXSTACK_DISABLE_X)
vm_flags &= ~VM_EXEC;
vm_flags |= mm->def_flags;
+ vm_flags |= VM_STACK_INCOMPLETE_SETUP;
ret = mprotect_fixup(vma, &prev, vma->vm_start, vma->vm_end,
vm_flags);
@@ -630,6 +632,9 @@ int setup_arg_pages(struct linux_binprm *bprm,
goto out_unlock;
}
+ /* mprotect_fixup is overkill to remove the temporary stack flags */
+ vma->vm_flags &= ~VM_STACK_INCOMPLETE_SETUP;
+
stack_expand = 131072UL; /* randomly 32*4k (or 2*64k) pages */
stack_size = vma->vm_end - vma->vm_start;
/*