From 11ac552477e32835cb6970bf0a70c210807f5673 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sat, 14 Aug 2010 11:44:56 -0700 Subject: [PATCH] mm: fix page table unmap for stack guard page properly MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit We do in fact need to unmap the page table _before_ doing the whole stack guard page logic, because if it is needed (mainly 32-bit x86 with PAE and CONFIG_HIGHPTE, but other architectures may use it too) then it will do a kmap_atomic/kunmap_atomic. And those kmaps will create an atomic region that we cannot do allocations in. However, the whole stack expand code will need to do anon_vma_prepare() and vma_lock_anon_vma() and they cannot do that in an atomic region. Now, a better model might actually be to do the anon_vma_prepare() when _creating_ a VM_GROWSDOWN segment, and not have to worry about any of this at page fault time. But in the meantime, this is the straightforward fix for the issue. See https://bugzilla.kernel.org/show_bug.cgi?id=16588 for details. Reported-by: Wylda Reported-by: Sedat Dilek Reported-by: Mike Pagano Reported-by: François Valenduc Tested-by: Ed Tomlinson Cc: Pekka Enberg Cc: Greg KH Cc: stable@kernel.org Signed-off-by: Linus Torvalds --- mm/memory.c | 15 +++++++-------- 1 file changed, 7 insertions(+), 8 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 9b3b73f4ae9c..b6e5fd23cc5a 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2792,24 +2792,23 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma, spinlock_t *ptl; pte_t entry; - if (check_stack_guard_page(vma, address) < 0) { - pte_unmap(page_table); - return VM_FAULT_SIGBUS; - } + pte_unmap(page_table); + /* Check if we need to add a guard page to the stack */ + if (check_stack_guard_page(vma, address) < 0) + return VM_FAULT_SIGBUS; + + /* Use the zero-page for reads */ if (!(flags & FAULT_FLAG_WRITE)) { entry = pte_mkspecial(pfn_pte(my_zero_pfn(address), vma->vm_page_prot)); - ptl = pte_lockptr(mm, pmd); - spin_lock(ptl); + page_table = pte_offset_map_lock(mm, pmd, address, &ptl); if (!pte_none(*page_table)) goto unlock; goto setpte; } /* Allocate our own private page. */ - pte_unmap(page_table); - if (unlikely(anon_vma_prepare(vma))) goto oom; page = alloc_zeroed_user_highpage_movable(vma, address);