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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 F1464C43214 for ; Sun, 8 Aug 2021 02:07:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D69B360F5C for ; Sun, 8 Aug 2021 02:07:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230148AbhHHCIO (ORCPT ); Sat, 7 Aug 2021 22:08:14 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45478 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229882AbhHHCIL (ORCPT ); Sat, 7 Aug 2021 22:08:11 -0400 Received: from mail-pj1-x102c.google.com (mail-pj1-x102c.google.com [IPv6:2607:f8b0:4864:20::102c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A88B3C061760; Sat, 7 Aug 2021 19:07:53 -0700 (PDT) Received: by mail-pj1-x102c.google.com with SMTP id s22-20020a17090a1c16b0290177caeba067so28793796pjs.0; Sat, 07 Aug 2021 19:07:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=1KFCzgzs6/mkJLTZRMdu7KL4aRMw+QDalF1MyA5qyPc=; b=c1jmo4avM+j7qm/Hvn4rEviWxWdp0pbR8TMWAvIa31LCIWFMHOZDm7tiys7Czcb+26 CBtHJ07AbujN0rJgMi1sRutrTqJV0PR/Vx5LI3MHcT7nwIjcvyOhVlfqDZdjx+9zCeds nTjLHdGvAfcJoDzCFcdmi4aNHdrP6PF0C72yVYyXjbB88jvhpV1HuNKPlaQlU4Wkrc3F 2slbAD7Ve6CiwjOKbnIfKm6JM0BnL20IQvycWHiaNZBJw10ZWYCwqTuvZjt+jZszQSE6 wCrGbsO+HvUN/cd4AzMzRZoFrZku4zo8ndOU6uR2CJm0ELT5gvIlDhbF72QvPVUZ7laM v+9A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=1KFCzgzs6/mkJLTZRMdu7KL4aRMw+QDalF1MyA5qyPc=; b=j7E62lT9sLDriE33PY3NKP4cOojwZrdNcFXpdsiYNhbR/PDJ4dDxfmVZaCoquU4EZk vnKKNL59PBYq9cjup874xjBiNLivR0suh/2KILqF4LtUhcK6GiE9EDMsvPGtWyVEwII6 RDTJ+b9r+a/Qv3VY4X/38VO/rbxY8auZH7uRkmmRzf5Y6ryi+FJst5ys/BSv7gczRnS8 FjpcAb9QAW1Qto6bTHAfGaXUHGc0fdqRh8vCrgu6azNtbjFeU0yrg4qeo8bdRbH5CFrQ OW+6j5wrBG8tYVLYnHcmh+F2UgagJ4DWPAiTMA2Nv3J0UwsV3cYiVEZAK6yGu8sZxGXy npuw== X-Gm-Message-State: AOAM533ntTnYMK5e+1hb7Kr6MyW9EdoqwZPLxnBKd8mVspSrfRk4PpJA WkjvRbE/9tDABpavtA5vKZFFRpEGtxKD/A== X-Google-Smtp-Source: ABdhPJytvGw2/Z+5f1wuXCQ77/SUg5Bv0uYeWV5Hra0kqSaDResaqJ/hxaWnIOzmCfUPHdwMjak1Tg== X-Received: by 2002:a05:6a00:c81:b029:30e:21bf:4c15 with SMTP id a1-20020a056a000c81b029030e21bf4c15mr17944810pfv.70.1628388473101; Sat, 07 Aug 2021 19:07:53 -0700 (PDT) Received: from sc2-haas01-esx0118.eng.vmware.com ([66.170.99.1]) by smtp.gmail.com with ESMTPSA id o18sm3987432pjp.1.2021.08.07.19.07.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 07 Aug 2021 19:07:52 -0700 (PDT) From: Nadav Amit X-Google-Original-From: Nadav Amit To: Andrew Morton Cc: Pavel Emelyanov , Mike Rapoport , Peter Xu , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Nadav Amit , Jens Axboe , Andrea Arcangeli , Alexander Viro , io-uring@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 3/3] selftests/vm/userfaultfd: wake after copy failure Date: Sat, 7 Aug 2021 19:07:24 -0700 Message-Id: <20210808020724.1022515-4-namit@vmware.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210808020724.1022515-1-namit@vmware.com> References: <20210808020724.1022515-1-namit@vmware.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Nadav Amit When userfaultfd copy-ioctl fails since the PTE already exists, an -EEXIST error is returned and the faulting thread is not woken. The current userfaultfd test does not wake the faulting thread in such case. The assumption is presumably that another thread set the PTE through copy/wp ioctl and would wake the faulting thread or that alternatively the fault handler would realize there is no need to "must_wait" and continue. This is not necessarily true. There is an assumption that the "must_wait" tests in handle_userfault() are sufficient to provide definitive answer whether the offending PTE is populated or not. However, userfaultfd_must_wait() test is lockless. Consequently, concurrent calls to ptep_modify_prot_start(), for instance, can clear the PTE and can cause userfaultfd_must_wait() to wrongly assume it is not populated and a wait is needed. There are therefore 3 options: (1) Change the tests to wake on copy failure. (2) Wake faulting thread unconditionally on zero/copy ioctls before returning -EEXIST. (3) Change the userfaultfd_must_wait() to hold locks. This patch took the first approach, but the others are valid solutions with different tradeoffs. Cc: Jens Axboe Cc: Andrea Arcangeli Cc: Peter Xu Cc: Alexander Viro Cc: io-uring@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Signed-off-by: Nadav Amit --- tools/testing/selftests/vm/userfaultfd.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/tools/testing/selftests/vm/userfaultfd.c b/tools/testing/selftests/vm/userfaultfd.c index 2ea438e6b8b1..10ab56c2484a 100644 --- a/tools/testing/selftests/vm/userfaultfd.c +++ b/tools/testing/selftests/vm/userfaultfd.c @@ -566,6 +566,18 @@ static void retry_copy_page(int ufd, struct uffdio_copy *uffdio_copy, } } +static void wake_range(int ufd, unsigned long addr, unsigned long len) +{ + struct uffdio_range uffdio_wake; + + uffdio_wake.start = addr; + uffdio_wake.len = len; + + if (ioctl(ufd, UFFDIO_WAKE, &uffdio_wake)) + fprintf(stderr, "error waking %lu\n", + addr), exit(1); +} + static int __copy_page(int ufd, unsigned long offset, bool retry) { struct uffdio_copy uffdio_copy; @@ -585,6 +597,7 @@ static int __copy_page(int ufd, unsigned long offset, bool retry) if (uffdio_copy.copy != -EEXIST) err("UFFDIO_COPY error: %"PRId64, (int64_t)uffdio_copy.copy); + wake_range(ufd, uffdio_copy.dst, page_size); } else if (uffdio_copy.copy != page_size) { err("UFFDIO_COPY error: %"PRId64, (int64_t)uffdio_copy.copy); } else { -- 2.25.1