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=-16.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 40E89C4338F for ; Wed, 11 Aug 2021 20:14:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 165F661019 for ; Wed, 11 Aug 2021 20:14:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231705AbhHKUOY (ORCPT ); Wed, 11 Aug 2021 16:14:24 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53510 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229655AbhHKUOX (ORCPT ); Wed, 11 Aug 2021 16:14:23 -0400 Received: from mail-yb1-xb30.google.com (mail-yb1-xb30.google.com [IPv6:2607:f8b0:4864:20::b30]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED0ADC061765 for ; Wed, 11 Aug 2021 13:13:59 -0700 (PDT) Received: by mail-yb1-xb30.google.com with SMTP id k65so6961439yba.13 for ; Wed, 11 Aug 2021 13:13:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=broadcom.com; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=u+HEwVE2h6EoXNkQ9h0qH6PYXrhFQild+sFaHXOY9kI=; b=XMxA2B/D7RDRfSgA8nxbJElMjvXuarvNNnxSWpgAMLGLtTw2f4D3Zf1gGWdVmn8ZZN iJrIhJns9KCW2FIAVUh11DIg0Y276EecZbvi9HpE9SC9Fdcqz01nLTkRY2/A4D8LSVPh SDa3wJfFz4Jiv6TPQ6tV4mTvemuNU839Wzhug= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=u+HEwVE2h6EoXNkQ9h0qH6PYXrhFQild+sFaHXOY9kI=; b=VZDoJK/iqeAOi5UIUf+hplYbpA8+bccnmBQpPutAaljX+3qRFoszIllt/KqU4HNVma lh8PATCKYjg/to1JtY14rZmlyQb4+yV3s1i9Kp2bTm7tN9Y59FFgYIUXjvIQbCTcFCsQ AiJOl1p11+kaDLCfFq5hyLd2LEbnIZfNZKBPXG5/Bim3wNaHrrAkqYkNGUIlkmMqW9fY j3BuHBEMyCd+eNQwghTA3ghmtLTI4CDUoDWlkzW8joKdHByk2lSySQwlsZm/Vs4CxNJ2 XFmeHDTFBewQ11+QacFUnjmUySi7VbCuUV6jCcteayylfVsfvPpmttPjSkIl3HwOQ0NB G73Q== X-Gm-Message-State: AOAM530qFARU5gJ97j1fJBhpsEPFyiLUDnG3Ysvj1vY1aqHlIGOd1A3J UBzHKf3QHR7NqXIAoQ6ZqcNw3V9x2eLPurU09v3f3w== X-Google-Smtp-Source: ABdhPJwTJe8JT59DUTqZKNtqmV/D6pYWLYyNPMNcEZ002/haODay4E4hPF7oVM80OPrFTTAYvi7phY05y668+LuwclA= X-Received: by 2002:a25:65c4:: with SMTP id z187mr291934ybb.400.1628712838924; Wed, 11 Aug 2021 13:13:58 -0700 (PDT) MIME-Version: 1.0 References: <20210811193239.3155396-1-kuba@kernel.org> <20210811193239.3155396-2-kuba@kernel.org> In-Reply-To: <20210811193239.3155396-2-kuba@kernel.org> From: Edwin Peer Date: Wed, 11 Aug 2021 13:13:22 -0700 Message-ID: Subject: Re: [PATCH net 1/4] bnxt: don't lock the tx queue from napi poll To: Jakub Kicinski Cc: "David S . Miller" , Michael Chan , Jeffrey Huang , Eddie Wai , Prashant Sreedharan , Andrew Gospodarek , netdev Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Wed, Aug 11, 2021 at 12:32 PM Jakub Kicinski wrote: > > We can't take the tx lock from the napi poll routine, because > netpoll can poll napi at any moment, including with the tx lock > already held. > > It seems that the tx lock is only protecting against the disable > path, appropriate barriers are already in place to make sure > cleanup can safely run concurrently with start_xmit. I don't see > any other reason why 'stopped && avail > thresh' needs to be > re-checked under the lock. > > Remove the tx lock and use synchronize_net() to make sure > closing the device does not race we restarting the queues. > Annotate accesses to dev_state against data races. > > Fixes: c0c050c58d84 ("bnxt_en: New Broadcom ethernet driver.") > Signed-off-by: Jakub Kicinski > --- > drivers/net/ethernet/broadcom/bnxt/bnxt.c | 21 ++++++++++----------- > 1 file changed, 10 insertions(+), 11 deletions(-) > > diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt.c b/drivers/net/ethernet/broadcom/bnxt/bnxt.c > index 865fcb8cf29f..07827d6b0fec 100644 > --- a/drivers/net/ethernet/broadcom/bnxt/bnxt.c > +++ b/drivers/net/ethernet/broadcom/bnxt/bnxt.c > @@ -730,15 +730,10 @@ static void bnxt_tx_int(struct bnxt *bp, struct bnxt_napi *bnapi, int nr_pkts) > */ > smp_mb(); > > - if (unlikely(netif_tx_queue_stopped(txq)) && > - (bnxt_tx_avail(bp, txr) > bp->tx_wake_thresh)) { > - __netif_tx_lock(txq, smp_processor_id()); > - if (netif_tx_queue_stopped(txq) && > - bnxt_tx_avail(bp, txr) > bp->tx_wake_thresh && > - txr->dev_state != BNXT_DEV_STATE_CLOSING) > - netif_tx_wake_queue(txq); > - __netif_tx_unlock(txq); > - } > + if (netif_tx_queue_stopped(txq) && Probably worth retaining the unlikely() that the original outer check had. > + bnxt_tx_avail(bp, txr) > bp->tx_wake_thresh && > + READ_ONCE(txr->dev_state) != BNXT_DEV_STATE_CLOSING) > + netif_tx_wake_queue(txq); > } > > static struct page *__bnxt_alloc_rx_page(struct bnxt *bp, dma_addr_t *mapping, > @@ -9264,9 +9259,11 @@ void bnxt_tx_disable(struct bnxt *bp) > if (bp->tx_ring) { > for (i = 0; i < bp->tx_nr_rings; i++) { > txr = &bp->tx_ring[i]; > - txr->dev_state = BNXT_DEV_STATE_CLOSING; > + WRITE_ONCE(txr->dev_state, BNXT_DEV_STATE_CLOSING); > } > } > + /* Make sure napi polls see @dev_state change */ > + synchronize_net(); > /* Drop carrier first to prevent TX timeout */ > netif_carrier_off(bp->dev); > /* Stop all TX queues */ > @@ -9280,8 +9277,10 @@ void bnxt_tx_enable(struct bnxt *bp) > > for (i = 0; i < bp->tx_nr_rings; i++) { > txr = &bp->tx_ring[i]; > - txr->dev_state = 0; > + WRITE_ONCE(txr->dev_state, 0); > } > + /* Make sure napi polls see @dev_state change */ > + synchronize_net(); > netif_tx_wake_all_queues(bp->dev); > if (bp->link_info.link_up) > netif_carrier_on(bp->dev); > -- > 2.31.1 Regards, Edwin Peer