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=-19.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 BEAD6C432BE for ; Thu, 2 Sep 2021 07:03:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 97D86610C9 for ; Thu, 2 Sep 2021 07:03:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242956AbhIBHEb (ORCPT ); Thu, 2 Sep 2021 03:04:31 -0400 Received: from smtp-fw-6002.amazon.com ([52.95.49.90]:50095 "EHLO smtp-fw-6002.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242875AbhIBHEb (ORCPT ); Thu, 2 Sep 2021 03:04:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1630566214; x=1662102214; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=aNvIJIxasNCrDoXPix03/CFYbVuPbiGgTXIiPFUnDfI=; b=jsLtPZHYIHN/ENwggNdhti4m/ArKIs/Q/9OH1m8zpO/7VqvL5Mr4I6AG du6j6KAzC/UiJSD2IXlpORVpsXziziUYIotcGRoGBY8ZZ5np5wqhcaHK3 2oxWdwcJQa0PCPqY2Gx2wZF2d+SpfI0Qfr+GmNyphaLn0/a0uXJdzunYY Y=; X-IronPort-AV: E=Sophos;i="5.84,371,1620691200"; d="scan'208";a="137256772" Received: from iad12-co-svc-p1-lb1-vlan2.amazon.com (HELO email-inbound-relay-1e-28209b7b.us-east-1.amazon.com) ([10.43.8.2]) by smtp-border-fw-6002.iad6.amazon.com with ESMTP; 02 Sep 2021 07:03:27 +0000 Received: from EX13D19EUB003.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-1e-28209b7b.us-east-1.amazon.com (Postfix) with ESMTPS id 09EE9BBC59; Thu, 2 Sep 2021 07:03:24 +0000 (UTC) Received: from 8c85908914bf.ant.amazon.com (10.43.161.176) by EX13D19EUB003.ant.amazon.com (10.43.166.69) with Microsoft SMTP Server (TLS) id 15.0.1497.23; Thu, 2 Sep 2021 07:03:20 +0000 Subject: Re: [PATCH for-next 4/4] RDMA/efa: CQ notifications To: Jason Gunthorpe CC: Doug Ledford , , Alexander Matushevsky , Firas JahJah , Yossi Leybovich References: <20210811151131.39138-1-galpress@amazon.com> <20210811151131.39138-5-galpress@amazon.com> <20210820182702.GA550455@nvidia.com> <7a4963ea-f028-e787-a5ba-fabf907c6d6b@amazon.com> <20210901115716.GG1721383@nvidia.com> <20210901153659.GL1721383@nvidia.com> From: Gal Pressman Message-ID: Date: Thu, 2 Sep 2021 10:03:16 +0300 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20210901153659.GL1721383@nvidia.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.43.161.176] X-ClientProxiedBy: EX13D17UWB002.ant.amazon.com (10.43.161.141) To EX13D19EUB003.ant.amazon.com (10.43.166.69) Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On 01/09/2021 18:36, Jason Gunthorpe wrote: > On Wed, Sep 01, 2021 at 05:24:43PM +0300, Gal Pressman wrote: >> On 01/09/2021 14:57, Jason Gunthorpe wrote: >>> On Wed, Sep 01, 2021 at 02:50:42PM +0300, Gal Pressman wrote: >>>> On 20/08/2021 21:27, Jason Gunthorpe wrote: >>>>> On Wed, Aug 11, 2021 at 06:11:31PM +0300, Gal Pressman wrote: >>>>>> diff --git a/drivers/infiniband/hw/efa/efa_main.c b/drivers/infiniband/hw/efa/efa_main.c >>>>>> index 417dea5f90cf..29db4dec02f0 100644 >>>>>> +++ b/drivers/infiniband/hw/efa/efa_main.c >>>>>> @@ -67,6 +67,46 @@ static void efa_release_bars(struct efa_dev *dev, int bars_mask) >>>>>> pci_release_selected_regions(pdev, release_bars); >>>>>> } >>>>>> >>>>>> +static void efa_process_comp_eqe(struct efa_dev *dev, struct efa_admin_eqe *eqe) >>>>>> +{ >>>>>> + u16 cqn = eqe->u.comp_event.cqn; >>>>>> + struct efa_cq *cq; >>>>>> + >>>>>> + cq = xa_load(&dev->cqs_xa, cqn); >>>>>> + if (unlikely(!cq)) { >>>>> >>>>> This seems unlikely to be correct, what prevents cq from being >>>>> destroyed concurrently? >>>>> >>>>> A comp_handler cannot be running after cq destroy completes. >>>> >>>> Sorry for the long turnaround, was OOO. >>>> >>>> The CQ cannot be destroyed until all completion events are acked. >>>> https://github.com/linux-rdma/rdma-core/blob/7fd01f0c6799f0ecb99cae03c22cf7ff61ffbf5a/libibverbs/man/ibv_get_cq_event.3#L45 >>>> https://github.com/linux-rdma/rdma-core/blob/7fd01f0c6799f0ecb99cae03c22cf7ff61ffbf5a/libibverbs/cmd_cq.c#L208 >>> >>> That is something quite different, and in userspace. >>> >>> What in the kernel prevents tha xa_load and the xa_erase from racing together? >> >> Good point. >> I think we need to surround efa_process_comp_eqe() with an rcu_read_lock() and >> have a synchronize_rcu() after removing it from the xarray in >> destroy_cq. > > Try to avoid synchronize_rcu() I don't see how that's possible? >> Though I'd like to avoid copy-pasting xa_load() in order to use the >> advanced xas_load() function. > > Why would you need that? Just call xa_load() while holding the > rcu_read_lock() if that is what you want. Can you put the whole > function under the rcu_read_lock()? Sure, I wasn't sure if it's OK to nest rcu_read_lock() calls. >> Do you have any better ideas? > > Other common alternative is to use the xa_lock(), but that doesn't > seem suitable for an EQ Right, I think I'll go with the rcu approach.