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=-11.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS 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 94C5AC4708F for ; Tue, 1 Jun 2021 00:37:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6B7086124B for ; Tue, 1 Jun 2021 00:37:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232573AbhFAAjQ (ORCPT ); Mon, 31 May 2021 20:39:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:35704 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232366AbhFAAjO (ORCPT ); Mon, 31 May 2021 20:39:14 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id A7C40611CB; Tue, 1 Jun 2021 00:37:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1622507853; bh=hSbXTlNRap0TMykMgzRT7IHS4sVlT83yO/koAonPLlA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=RBTnngxJml+laVwubXrQR8E8jWDxGtOczjthaJsEsiFZEGtTS2TxAFAS3cMh/hQb3 +IUuEX8weZK4X1Clyws1J/IpWtKNfwgoTfieywpzzejOM99a+Xtfq83W5qfkQ4ZkyN l00OS8KceYts5fsaG+zTfmJ94VoKP9ElU/lLTeQY= Date: Mon, 31 May 2021 17:37:33 -0700 From: Andrew Morton To: Mina Almasry Cc: Axel Rasmussen , Peter Xu , linux-mm@kvack.org, Mike Kravetz , linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v4] mm, hugetlb: Fix simple resv_huge_pages underflow on UFFDIO_COPY Message-Id: <20210531173733.615fd539396ff7a173a2bf8b@linux-foundation.org> In-Reply-To: <20210528004649.85298-1-almasrymina@google.com> References: <20210528004649.85298-1-almasrymina@google.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 27 May 2021 17:46:49 -0700 Mina Almasry wrote: > The userfaultfd hugetlb tests detect a resv_huge_pages underflow. This > happens when hugetlb_mcopy_atomic_pte() is called with !is_continue on > an index for which we already have a page in the cache. When this > happens, we allocate a second page, double consuming the reservation, > and then fail to insert the page into the cache and return -EEXIST. > > To fix this, we first if there exists a page in the cache which already > consumed the reservation, and return -EEXIST immediately if so. > > There is still a rare condition where we fail to copy the page contents > AND race with a call for hugetlb_no_page() for this index and again we > will underflow resv_huge_pages. That is fixed in a more complicated > patch not targeted for -stable. > > Test: > Hacked the code locally such that resv_huge_pages underflows produce > a warning, then: > > ./tools/testing/selftests/vm/userfaultfd hugetlb_shared 10 > 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success > ./tools/testing/selftests/vm/userfaultfd hugetlb 10 > 2 /tmp/kokonut_test/huge/userfaultfd_test && echo test success > > Both tests succeed and produce no warnings. After the > test runs number of free/resv hugepages is correct. > > Signed-off-by: Mina Almasry > Cc: Axel Rasmussen > Cc: Peter Xu > Cc: linux-mm@kvack.org > Cc: Mike Kravetz > Cc: Andrew Morton > Cc: linux-mm@kvack.org > Cc: linux-kernel@vger.kernel.org > Cc: stable@vger.kernel.org Do we have a Fixes: for this, or is it an always-been-there issue?