From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 45F9BC43381 for ; Sat, 2 Mar 2019 17:11:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0AA2220836 for ; Sat, 2 Mar 2019 17:11:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="E69ej4bw" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726960AbfCBRLM (ORCPT ); Sat, 2 Mar 2019 12:11:12 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:58504 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726368AbfCBRLM (ORCPT ); Sat, 2 Mar 2019 12:11:12 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=kl5e37WI7w9hPYD4s95DfL0cvVBczbmwLkcTsoBgW1o=; b=E69ej4bwFLApvoJgbCNCL59MA 09sYMmuFN2CRP+jsSrQ489rnRpZ+PxTpVsoa8+j9uB5h4i2twJJrUUr4pozB4CFd3tKbMhT8Vjr9h 71HnjqpdyASNmSFaF/SWjvkIsi+nucHv5h93bAkoNWm6TUQgBwGtbmfmNLln1k2qo6pURI13Ymn9A 3pdyMcBRbquct9OXX6mRNcdYt0E7wSb8jDCmGOEaDwUmaOxmp++RTfTzPmUtFN0kTGzM9mvncRoNJ yLLiOMFp6cm1hv/BJqG9d3Su7PqLLXpSzHiEQehqE6oxqxaHKek2RldjAQbW37hmwdIZLDjUZLOVG vvJcw3p1Q==; Received: from willy by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1h089s-0004Ts-1J; Sat, 02 Mar 2019 17:10:44 +0000 Date: Sat, 2 Mar 2019 09:10:43 -0800 From: Matthew Wilcox To: Jan Stancek Cc: linux-mm@kvack.org, akpm@linux-foundation.org, peterz@infradead.org, riel@surriel.com, mhocko@suse.com, ying.huang@intel.com, jrdr.linux@gmail.com, jglisse@redhat.com, aneesh.kumar@linux.ibm.com, david@redhat.com, aarcange@redhat.com, raquini@redhat.com, rientjes@google.com, kirill@shutemov.name, mgorman@techsingularity.net, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/memory.c: do_fault: avoid usage of stale vm_area_struct Message-ID: <20190302171043.GP11592@bombadil.infradead.org> References: <0b7a4604529e16ace8d65a42dac7c78582e7fb28.1551538524.git.jstancek@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0b7a4604529e16ace8d65a42dac7c78582e7fb28.1551538524.git.jstancek@redhat.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Mar 02, 2019 at 04:11:26PM +0100, Jan Stancek wrote: > Problem is that "vmf->vma" used in do_fault() can become stale. > Because mmap_sem may be released, other threads can come in, > call munmap() and cause "vma" be returned to kmem cache, and > get zeroed/re-initialized and re-used: > This patch pins mm_struct and stores its value, to avoid using > potentially stale "vma" when calling pte_free(). OK, we need to cache the mm_struct, but why do we need the extra atomic op? There's surely no way the mm can be freed while the thread is in the middle of handling a fault. ie I would drop these lines: > + mmgrab(vm_mm); > + ... > + > + mmdrop(vm_mm); > +