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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 34B54C433E1 for ; Mon, 18 May 2020 17:50:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 07C4A207F5 for ; Mon, 18 May 2020 17:50:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589824253; bh=+XG6YDhVnmYYUPoMUfzP6DZO8i8Iskzc9nZALxpTZCA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=MAeVWchdxAPP/x5zFghY3w8U5UxBpF3ywoYiq3TxRU0FUGrs8F/BiXq2qlQad5LYq Acw9scbWzmal0mg+tahe7tvMD/N9daZIjvd5DEAGefBjEE6xH3jZJO8Z9aNAahhKOW bH1gks8aDuw1GRKBn7o/H0N30oe9Z6JnD3cJZuVU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730728AbgERRuv (ORCPT ); Mon, 18 May 2020 13:50:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:53038 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730779AbgERRup (ORCPT ); Mon, 18 May 2020 13:50:45 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.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 62CBD20715; Mon, 18 May 2020 17:50:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589824244; bh=+XG6YDhVnmYYUPoMUfzP6DZO8i8Iskzc9nZALxpTZCA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lkNMU3y3B3C5BsUBSfZwemgjbhxeMJxzbSHGhUIqMvV6VMGl8qHIardJQHA/AnZ7N /9YUBbSSHo8Fd64zLjIPKpVLnsy4evglDWBtKbVP5Fq+E2WRGyfDvpo/OLSKS7gbcO 3BWD1Ag3nLUvjjGO+kUBaP45Xpe8LOf8z3OLeFbU= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Thomas Gleixner , Eric Dumazet , "Michael S. Tsirkin" , "David S. Miller" Subject: [PATCH 4.19 15/80] virtio_net: fix lockdep warning on 32 bit Date: Mon, 18 May 2020 19:36:33 +0200 Message-Id: <20200518173453.507244143@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200518173450.097837707@linuxfoundation.org> References: <20200518173450.097837707@linuxfoundation.org> User-Agent: quilt/0.66 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 From: "Michael S. Tsirkin" [ Upstream commit 01c3259818a11f3cc3cd767adbae6b45849c03c1 ] When we fill up a receive VQ, try_fill_recv currently tries to count kicks using a 64 bit stats counter. Turns out, on a 32 bit kernel that uses a seqcount. sequence counts are "lock" constructs where you need to make sure that writers are serialized. In turn, this means that we mustn't run two try_fill_recv concurrently. Which of course we don't. We do run try_fill_recv sometimes from a softirq napi context, and sometimes from a fully preemptible context, but the later always runs with napi disabled. However, when it comes to the seqcount, lockdep is trying to enforce the rule that the same lock isn't accessed from preemptible and softirq context - it doesn't know about napi being enabled/disabled. This causes a false-positive warning: WARNING: inconsistent lock state ... inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage. As a work around, shut down the warning by switching to u64_stats_update_begin_irqsave - that works by disabling interrupts on 32 bit only, is a NOP on 64 bit. Reported-by: Thomas Gleixner Suggested-by: Eric Dumazet Signed-off-by: Michael S. Tsirkin Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- drivers/net/virtio_net.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/drivers/net/virtio_net.c +++ b/drivers/net/virtio_net.c @@ -1242,9 +1242,11 @@ static bool try_fill_recv(struct virtnet break; } while (rq->vq->num_free); if (virtqueue_kick_prepare(rq->vq) && virtqueue_notify(rq->vq)) { - u64_stats_update_begin(&rq->stats.syncp); + unsigned long flags; + + flags = u64_stats_update_begin_irqsave(&rq->stats.syncp); rq->stats.kicks++; - u64_stats_update_end(&rq->stats.syncp); + u64_stats_update_end_irqrestore(&rq->stats.syncp, flags); } return !oom;