From de51257aa301652876ab6e8f13ea4eadbe4a3846 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Fri, 30 Jul 2010 10:58:26 -0700 Subject: [PATCH] mm: fix ia64 crash when gcore reads gate area Debian's ia64 autobuilders have been seeing kernel freeze or reboot when running the gdb testsuite (Debian bug 588574): dannf bisected to 2.6.32 62eede62dafb4a6633eae7ffbeb34c60dba5e7b1 "mm: ZERO_PAGE without PTE_SPECIAL"; and reproduced it with gdb's gcore on a simple target. I'd missed updating the gate_vma handling in __get_user_pages(): that happens to use vm_normal_page() (nowadays failing on the zero page), yet reported success even when it failed to get a page - boom when access_process_vm() tried to copy that to its intermediate buffer. Fix this, resisting cleanups: in particular, leave it for now reporting success when not asked to get any pages - very probably safe to change, but let's not risk it without testing exposure. Why did ia64 crash with 16kB pages, but succeed with 64kB pages? Because setup_gate() pads each 64kB of its gate area with zero pages. Reported-by: Andreas Barth Bisected-by: dann frazier Signed-off-by: Hugh Dickins Tested-by: dann frazier Cc: stable@kernel.org Signed-off-by: Linus Torvalds --- mm/memory.c | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index 119b7ccdf39b..bde42c6d3633 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1394,10 +1394,20 @@ int __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, return i ? : -EFAULT; } if (pages) { - struct page *page = vm_normal_page(gate_vma, start, *pte); + struct page *page; + + page = vm_normal_page(gate_vma, start, *pte); + if (!page) { + if (!(gup_flags & FOLL_DUMP) && + is_zero_pfn(pte_pfn(*pte))) + page = pte_page(*pte); + else { + pte_unmap(pte); + return i ? : -EFAULT; + } + } pages[i] = page; - if (page) - get_page(page); + get_page(page); } pte_unmap(pte); if (vmas)