From a8bef8ff6ea15fa4c67433cab0f5f3484574ef7c Mon Sep 17 00:00:00 2001 From: Mel Gorman Date: Mon, 24 May 2010 14:32:24 -0700 Subject: 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: [] handle_mm_fault+0x3f8/0x76a [] do_page_fault+0x44a/0x46e [] page_fault+0x25/0x30 [] load_elf_binary+0x152a/0x192b [] search_binary_handler+0x173/0x313 [] do_execve+0x219/0x30a [] sys_execve+0x43/0x5e [] stub_execve+0x6a/0xc0 RIP [] 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 Reviewed-by: KAMEZAWA Hiroyuki Reviewed-by: Rik van Riel Acked-by: Linus Torvalds Cc: Minchan Kim Cc: Christoph Lameter Cc: Andrea Arcangeli Cc: Rik van Riel Cc: Peter Zijlstra Reviewed-by: KOSAKI Motohiro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/exec.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) (limited to 'fs') diff --git a/fs/exec.c b/fs/exec.c index e6e94c6..9badbc0 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; /* -- cgit v1.1