From patchwork Mon Jan 24 18:43:53 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 534904 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7BB86C433EF for ; Tue, 25 Jan 2022 00:09:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2370682AbiAYAF6 (ORCPT ); Mon, 24 Jan 2022 19:05:58 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54272 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1851079AbiAXXbx (ORCPT ); Mon, 24 Jan 2022 18:31:53 -0500 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4B4F3C075D05; Mon, 24 Jan 2022 13:35:13 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id DFAEA614DA; Mon, 24 Jan 2022 21:35:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F398EC340E4; Mon, 24 Jan 2022 21:35:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1643060112; bh=Ss+KyW9+v4+zPtZvCbZxmRTFAjt5mNV30rcy4WIJht8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=yWNekzEQUQtqfBF5fITcfnD2mTnVfsxE84QV8hBwtkOu3Eb9Ej9/1DpOpzmw+aksj Nbkm6oyD1O4LwgU//ol81hQmwKtqbLk66WgCL/BawK3vTQJjVdg/Ou1qqfNAugcJOx JYE08hIMDtx5J+DcfxD8xO5ltwKE8SXr1AeHrqts= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Oleksandr Andrushchenko , Boris Ostrovsky , Juergen Gross Subject: [PATCH 5.16 0844/1039] xen/gntdev: fix unmap notification order Date: Mon, 24 Jan 2022 19:43:53 +0100 Message-Id: <20220124184153.659861284@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220124184125.121143506@linuxfoundation.org> References: <20220124184125.121143506@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Oleksandr Andrushchenko commit ce2f46f3531a03781181b7f4bd1ff9f8c5086e7e upstream. While working with Xen's libxenvchan library I have faced an issue with unmap notifications sent in wrong order if both UNMAP_NOTIFY_SEND_EVENT and UNMAP_NOTIFY_CLEAR_BYTE were requested: first we send an event channel notification and then clear the notification byte which renders in the below inconsistency (cli_live is the byte which was requested to be cleared on unmap): [ 444.514243] gntdev_put_map UNMAP_NOTIFY_SEND_EVENT map->notify.event 6 libxenvchan_is_open cli_live 1 [ 444.515239] __unmap_grant_pages UNMAP_NOTIFY_CLEAR_BYTE at 14 Thus it is not possible to reliably implement the checks like - wait for the notification (UNMAP_NOTIFY_SEND_EVENT) - check the variable (UNMAP_NOTIFY_CLEAR_BYTE) because it is possible that the variable gets checked before it is cleared by the kernel. To fix that we need to re-order the notifications, so the variable is first gets cleared and then the event channel notification is sent. With this fix I can see the correct order of execution: [ 54.522611] __unmap_grant_pages UNMAP_NOTIFY_CLEAR_BYTE at 14 [ 54.537966] gntdev_put_map UNMAP_NOTIFY_SEND_EVENT map->notify.event 6 libxenvchan_is_open cli_live 0 Cc: stable@vger.kernel.org Signed-off-by: Oleksandr Andrushchenko Reviewed-by: Boris Ostrovsky Link: https://lore.kernel.org/r/20211210092817.580718-1-andr2000@gmail.com Signed-off-by: Juergen Gross Signed-off-by: Greg Kroah-Hartman --- drivers/xen/gntdev.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/drivers/xen/gntdev.c +++ b/drivers/xen/gntdev.c @@ -250,13 +250,13 @@ void gntdev_put_map(struct gntdev_priv * if (!refcount_dec_and_test(&map->users)) return; + if (map->pages && !use_ptemod) + unmap_grant_pages(map, 0, map->count); + if (map->notify.flags & UNMAP_NOTIFY_SEND_EVENT) { notify_remote_via_evtchn(map->notify.event); evtchn_put(map->notify.event); } - - if (map->pages && !use_ptemod) - unmap_grant_pages(map, 0, map->count); gntdev_free_map(map); }