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 18FF0C432BE for ; Thu, 2 Sep 2021 15:09:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC25A60BD3 for ; Thu, 2 Sep 2021 15:09:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234375AbhIBPK4 (ORCPT ); Thu, 2 Sep 2021 11:10:56 -0400 Received: from smtp-fw-9102.amazon.com ([207.171.184.29]:50206 "EHLO smtp-fw-9102.amazon.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229941AbhIBPKz (ORCPT ); Thu, 2 Sep 2021 11:10:55 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.com; i=@amazon.com; q=dns/txt; s=amazon201209; t=1630595398; x=1662131398; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=kni1JpsktfVFVHw8WagEimKQPJk1Zs0ylSSGWCwdxuA=; b=fpKcY6uXRwLliZ58iTfhJ0uwzhEL+jDkX225eLhPo1ddyNiAcDFjxHfx Jck6K8A/BOrfQaQw26L9aWXTcpB/o2Nt3gcl3l60Cv3q+wCJv72QAxrgS m1Zbo7Ft2CFgdOQvCMwTzUCJ2ef3OosjLyMO6nrTr6OpfNPaad7at3zmu s=; X-IronPort-AV: E=Sophos;i="5.85,262,1624320000"; d="scan'208";a="157160592" Received: from pdx4-co-svc-p1-lb2-vlan3.amazon.com (HELO email-inbound-relay-1d-474bcd9f.us-east-1.amazon.com) ([10.25.36.214]) by smtp-border-fw-9102.sea19.amazon.com with ESMTP; 02 Sep 2021 15:09:51 +0000 Received: from EX13D19EUB003.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-1d-474bcd9f.us-east-1.amazon.com (Postfix) with ESMTPS id E80A9A1D2F; Thu, 2 Sep 2021 15:09:48 +0000 (UTC) Received: from 8c85908914bf.ant.amazon.com (10.43.162.164) by EX13D19EUB003.ant.amazon.com (10.43.166.69) with Microsoft SMTP Server (TLS) id 15.0.1497.23; Thu, 2 Sep 2021 15:09:44 +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> <20210902130255.GR1721383@nvidia.com> From: Gal Pressman Message-ID: <3a5fb37a-dd72-e322-f7c6-790ee4e04efa@amazon.com> Date: Thu, 2 Sep 2021 18:09:39 +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: <20210902130255.GR1721383@nvidia.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 7bit X-Originating-IP: [10.43.162.164] X-ClientProxiedBy: EX13D03UWC001.ant.amazon.com (10.43.162.136) To EX13D19EUB003.ant.amazon.com (10.43.166.69) Precedence: bulk List-ID: X-Mailing-List: linux-rdma@vger.kernel.org On 02/09/2021 16:02, Jason Gunthorpe wrote: > On Thu, Sep 02, 2021 at 10:03:16AM +0300, Gal Pressman wrote: >> 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? > > Usually people use call_rcu() instead Oh nice, thanks. I think the code would be much simpler using synchronize_rcu(), and the destroy_cq flow is usually on the cold path anyway. I also prefer to be certain that the CQ is freed once the destroy verb returns and not rely on the callback scheduling.