Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758853AbaGOLzD (ORCPT ); Tue, 15 Jul 2014 07:55:03 -0400 Received: from mga09.intel.com ([134.134.136.24]:41760 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758039AbaGOLzA (ORCPT ); Tue, 15 Jul 2014 07:55:00 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.01,665,1400050800"; d="scan'208";a="543565589" From: "Kirill A. Shutemov" To: Konstantin Khlebnikov Cc: "Kirill A. Shutemov" , Hugh Dickins , Ingo Korb , Ning Qu , Dave Jones , Sasha Levin , Andrew Morton , "linux-mm@kvack.org" , Linux Kernel Mailing List In-Reply-To: References: <748020aaaf5c5c2924a16232313e0175.squirrel@webmail.tu-dortmund.de> <20140715105547.C4832E00A3@blue.fi.intel.com> Subject: Re: PROBLEM: repeated remap_file_pages on tmpfs triggers bug on process exit Content-Transfer-Encoding: 7bit Message-Id: <20140715115456.32886E00A3@blue.fi.intel.com> Date: Tue, 15 Jul 2014 14:54:56 +0300 (EEST) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Konstantin Khlebnikov wrote: > On Tue, Jul 15, 2014 at 2:55 PM, Kirill A. Shutemov > wrote: > > Konstantin Khlebnikov wrote: > >> It seems boundng logic in do_fault_around is wrong: > >> > >> start_addr = max(address & fault_around_mask(), vma->vm_start); > >> off = ((address - start_addr) >> PAGE_SHIFT) & (PTRS_PER_PTE - 1); > >> pte -= off; > >> pgoff -= off; > >> > >> Ok, off <= 511, but it might be bigger than pte offset in pte table. > > > > I don't see how it possible: fault_around_mask() cannot be more than 0x1ff000 > > (x86-64, fault_around_bytes == 2M). It means start_addr will be aligned to 2M > > boundary in this case which is start of the page table pte belong to. > > > > Do I miss something? > > Nope, you're right. This fixes kernel crash but not the original problem. > > Problem is caused by calling do_fault_around for _non-linear_ faiult. > In this case pgoff is shifted and might become negative during calculation. > I'll send another patch. I've got to the same conclusion. My patch is below. >From dd761b693cd06c649499e913713ae5bc7c029f6e Mon Sep 17 00:00:00 2001 From: "Kirill A. Shutemov" Date: Tue, 15 Jul 2014 14:40:02 +0300 Subject: [PATCH] mm: avoid do_fault_around() on non-linear mappings Originally, I've wrongly assumed that non-linear mapping are always populated at least with pte_file() entries there, so !pte_none() check will catch them. It's not always the case: we can get there from __mm_populte in remap_file_pages() and pte will be clear. Let's put explicit check for non-linear mapping. This is a root cause of recent "kernel BUG at mm/filemap.c:202!". Signed-off-by: Kirill A. Shutemov Cc: stable@vger.kernel.org # 3.15+ --- mm/memory.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index d67fd9fcf1f2..440ad48266d6 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -2882,7 +2882,8 @@ static int do_read_fault(struct mm_struct *mm, struct vm_area_struct *vma, * if page by the offset is not ready to be mapped (cold cache or * something). */ - if (vma->vm_ops->map_pages && fault_around_pages() > 1) { + if (vma->vm_ops->map_pages && fault_around_pages() > 1 && + !(vma->vm_flags & VM_NONLINEAR)) { pte = pte_offset_map_lock(mm, pmd, address, &ptl); do_fault_around(vma, address, pte, pgoff, flags); if (!pte_same(*pte, orig_pte)) -- 2.0.1 -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/