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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 AE18BC433E1 for ; Thu, 13 Aug 2020 12:02:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 86ECD207DA for ; Thu, 13 Aug 2020 12:02:41 +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="wUkEP4gz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726612AbgHMMCi (ORCPT ); Thu, 13 Aug 2020 08:02:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47518 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726564AbgHMMBf (ORCPT ); Thu, 13 Aug 2020 08:01:35 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 63AE4C061757; Thu, 13 Aug 2020 05:00:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.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; bh=i41Yc10MxJ8SD/RmIm1p0LXK6Fe4vVxPBwR0fO9tHsU=; b=wUkEP4gznD8yhOKXfehUrg6u+p 4PCOcBf33WvByOdBvWwLPp6R8/WwxJlEYyQ3CY9ej+Zc55i7MERAd+5CuKACgEOMwJkJpICIjvu6D 4s1dRmOfQoghu7xdIO1fYpsEAEON7cEh4NTueg4+NtGD15C7xchhSji6EQqceguowmv1PUXzJ7Nts a0pAqKr+kEI15dkeOFh7FsqIvbIZKziG+7HYp+GACowqL/3hO1OafqdRTUrgk5GEc79FmzQH2KoHP UeKSdlIY4bl8Zozt8Pc5cSWRv3VGquq0YjgcJVVK0c7xUZQ0+VQiSFpdainJpwi+h0C1SJd8c8qzl p9a5QjuA==; Received: from willy by casper.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1k6Bu5-0003VD-3H; Thu, 13 Aug 2020 12:00:17 +0000 Date: Thu, 13 Aug 2020 13:00:17 +0100 From: Matthew Wilcox To: peterz@infradead.org Cc: Christoph Hellwig , Jacob Wen , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] block: insert a general SMP memory barrier before wake_up_bit() Message-ID: <20200813120017.GH17456@casper.infradead.org> References: <20200813024438.13170-1-jian.w.wen@oracle.com> <20200813073115.GA15436@infradead.org> <20200813114050.GW2674@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200813114050.GW2674@hirez.programming.kicks-ass.net> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Aug 13, 2020 at 01:40:50PM +0200, peterz@infradead.org wrote: > On Thu, Aug 13, 2020 at 08:31:15AM +0100, Christoph Hellwig wrote: > > On Thu, Aug 13, 2020 at 10:44:38AM +0800, Jacob Wen wrote: > > > wake_up_bit() uses waitqueue_active() that needs the explicit smp_mb(). > > > > Sounds like the barrier should go into wake_up_bit then.. > > Oh, thanks for reminding me.. > > https://lkml.kernel.org/r/20190624165012.GH3436@hirez.programming.kicks-ass.net > > I'll try and get back to that. +++ b/drivers/bluetooth/btmtkuart.c @@ -340,11 +340,8 @@ static int btmtkuart_recv_event(struct hci_dev *hdev, struct sk_buff *skb) if (hdr->evt == HCI_EV_VENDOR) { if (test_and_clear_bit(BTMTKUART_TX_WAIT_VND_EVT, - &bdev->tx_state)) { - /* Barrier to sync with other CPUs */ - smp_mb__after_atomic(); + &bdev->tx_state)) wake_up_bit(&bdev->tx_state, BTMTKUART_TX_WAIT_VND_EVT); - } } return 0; It'd be nice to be able to write: if (hdr->evt == HCI_EV_VENDOR) test_clear_and_wake_up_bit(&bdev->tx_state, BTMTKUART_TX_WAIT_VND_EVT); ... maybe with a better name.