From: Linus Torvalds Date: Sat, 14 Aug 2010 18:44:56 +0000 (-0700) Subject: mm: fix page table unmap for stack guard page properly X-Git-Tag: v2.6.27.52~2 X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=dd0e56723390426af45e74d6ae1850c7f473a193;p=karo-tx-linux.git mm: fix page table unmap for stack guard page properly commit 11ac552477e32835cb6970bf0a70c210807f5673 upstream. 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 Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- diff --git a/mm/memory.c b/mm/memory.c index 7e308fc2f961..f0282eb86508 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2428,14 +2428,13 @@ 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); + 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; - } /* 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);