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=-7.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 19B48C43441 for ; Mon, 19 Nov 2018 16:57:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D6C86214C1 for ; Mon, 19 Nov 2018 16:57:54 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="l24bqA+/" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org D6C86214C1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2404665AbeKTDWI (ORCPT ); Mon, 19 Nov 2018 22:22:08 -0500 Received: from mail.kernel.org ([198.145.29.99]:33688 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2403956AbeKTDWH (ORCPT ); Mon, 19 Nov 2018 22:22:07 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D8157206BA; Mon, 19 Nov 2018 16:57:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1542646672; bh=FaB3ja4W6D0/7o1+84j67F1IBOFaz3Q1G8zQ5cuOPsk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=l24bqA+/Ci3DHvVfMoW2EmR9kpjd4Nn1Un8ska5JJan5GXtl9q7+YONU7vvqVjYg8 pwSb0MJHUhJ07JT7GnW3AJip9/QAVoYWyTsNGhksf1oD//BN3QAjAm4obulyTEbZ6k L5Xgfd+/f1toAT3U2rBTurj8uKL2/p1lIjwEzStk= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Waiman.Long@hp.com, peterz@infradead.org, Juergen Gross , Jan Beulich Subject: [PATCH 4.4 046/160] xen: fix race in xen_qlock_wait() Date: Mon, 19 Nov 2018 17:28:05 +0100 Message-Id: <20181119162635.968352681@linuxfoundation.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20181119162630.031306128@linuxfoundation.org> References: <20181119162630.031306128@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Juergen Gross commit 2ac2a7d4d9ff4e01e36f9c3d116582f6f655ab47 upstream. In the following situation a vcpu waiting for a lock might not be woken up from xen_poll_irq(): CPU 1: CPU 2: CPU 3: takes a spinlock tries to get lock -> xen_qlock_wait() frees the lock -> xen_qlock_kick(cpu2) -> xen_clear_irq_pending() takes lock again tries to get lock -> *lock = _Q_SLOW_VAL -> *lock == _Q_SLOW_VAL ? -> xen_poll_irq() frees the lock -> xen_qlock_kick(cpu3) And cpu 2 will sleep forever. This can be avoided easily by modifying xen_qlock_wait() to call xen_poll_irq() only if the related irq was not pending and to call xen_clear_irq_pending() only if it was pending. Cc: stable@vger.kernel.org Cc: Waiman.Long@hp.com Cc: peterz@infradead.org Signed-off-by: Juergen Gross Reviewed-by: Jan Beulich Signed-off-by: Juergen Gross Signed-off-by: Greg Kroah-Hartman --- arch/x86/xen/spinlock.c | 15 +++++---------- 1 file changed, 5 insertions(+), 10 deletions(-) --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -47,17 +47,12 @@ static void xen_qlock_wait(u8 *byte, u8 if (irq == -1) return; - /* clear pending */ - xen_clear_irq_pending(irq); - barrier(); + /* If irq pending already clear it and return. */ + if (xen_test_irq_pending(irq)) { + xen_clear_irq_pending(irq); + return; + } - /* - * We check the byte value after clearing pending IRQ to make sure - * that we won't miss a wakeup event because of the clearing. - * - * The sync_clear_bit() call in xen_clear_irq_pending() is atomic. - * So it is effectively a memory barrier for x86. - */ if (READ_ONCE(*byte) != val) return;