From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f41.google.com (mail-wm0-f41.google.com [74.125.82.41]) by kanga.kvack.org (Postfix) with ESMTP id F08746B0038 for ; Mon, 23 Nov 2015 15:45:16 -0500 (EST) Received: by wmww144 with SMTP id w144so112898045wmw.1 for ; Mon, 23 Nov 2015 12:45:16 -0800 (PST) Received: from mail-wm0-x22f.google.com (mail-wm0-x22f.google.com. [2a00:1450:400c:c09::22f]) by mx.google.com with ESMTPS id r16si21873319wmb.2.2015.11.23.12.45.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 23 Nov 2015 12:45:15 -0800 (PST) Received: by wmec201 with SMTP id c201so122261325wme.1 for ; Mon, 23 Nov 2015 12:45:15 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1448309120-20911-1-git-send-email-toshi.kani@hpe.com> References: <1448309120-20911-1-git-send-email-toshi.kani@hpe.com> Date: Mon, 23 Nov 2015 12:45:15 -0800 Message-ID: Subject: Re: [PATCH] dax: Split pmd map when fallback on COW From: Dan Williams Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Toshi Kani Cc: "Kirill A. Shutemov" , Matthew Wilcox , Ross Zwisler , Linux MM , linux-fsdevel , "linux-nvdimm@lists.01.org" , "linux-kernel@vger.kernel.org" On Mon, Nov 23, 2015 at 12:05 PM, Toshi Kani wrote: > An infinite loop of PMD faults was observed when attempted to > mlock() a private read-only PMD mmap'd range of a DAX file. > > __dax_pmd_fault() simply returns with VM_FAULT_FALLBACK when > falling back to PTE on COW. However, __handle_mm_fault() > returns without falling back to handle_pte_fault() because > a PMD map is present in this case. > > Change __dax_pmd_fault() to split the PMD map, if present, > before returning with VM_FAULT_FALLBACK. > > Signed-off-by: Toshi Kani > Cc: Dan Williams > Cc: Kirill A. Shutemov > Cc: Matthew Wilcox > Cc: Ross Zwisler I thought the patch from Ross already addressed the infinite loop: https://patchwork.kernel.org/patch/7653731/ > --- > fs/dax.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/fs/dax.c b/fs/dax.c > index 43671b6..3405583 100644 > --- a/fs/dax.c > +++ b/fs/dax.c > @@ -546,8 +546,10 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address, > return VM_FAULT_FALLBACK; > > /* Fall back to PTEs if we're going to COW */ > - if (write && !(vma->vm_flags & VM_SHARED)) > + if (write && !(vma->vm_flags & VM_SHARED)) { > + split_huge_page_pmd(vma, address, pmd); > return VM_FAULT_FALLBACK; > + } > /* If the PMD would extend outside the VMA */ > if (pmd_addr < vma->vm_start) > return VM_FAULT_FALLBACK; This is a nop if CONFIG_TRANSPARENT_HUGEPAGE=n, so I don't think it's a complete fix. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org