From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1754223AbcKUMdK (ORCPT <rfc822;w@1wt.eu>);
        Mon, 21 Nov 2016 07:33:10 -0500
Received: from mail-wm0-f67.google.com ([74.125.82.67]:35754 "EHLO
        mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1753873AbcKUMdI (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 21 Nov 2016 07:33:08 -0500
Subject: Re: [PATCH v5 5/9] IB/isert: Replace semaphore sem with completion
To: Arnd Bergmann <arnd@arndb.de>
References: <1479708496-9828-1-git-send-email-binoy.jayan@linaro.org>
 <1479708496-9828-6-git-send-email-binoy.jayan@linaro.org>
 <e1e4788d-9250-d4c3-937f-262bd9264a76@grimberg.me>
 <2625189.HB0S3sfnY7@wuerfel>
Cc: Binoy Jayan <binoy.jayan@linaro.org>,
        Doug Ledford <dledford@redhat.com>, Sean Hefty <sean.hefty@intel.com>,
        Hal Rosenstock <hal.rosenstock@gmail.com>,
        Leon Romanovsky <leonro@mellanox.com>,
        Sagi Grimberg <sagig@mellanox.com>,
        Bart Van Assche <bart.vanassche@sandisk.com>,
        Nicholas Bellinger <nab@linux-iscsi.org>,
        Jenny Derzhavetz <jennyf@mellanox.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Steve Wise <swise@opengridcomputing.com>,
        Mark Bloch <markb@mellanox.com>,
        Tatyana E Nikolova <tatyana.e.nikolova@intel.com>,
        Matan Barak <matanb@mellanox.com>, Lijun Ou <oulijun@huawei.com>,
        "Wei Hu(Xavier)" <xavier.huwei@huawei.com>,
        Faisal Latif <faisal.latif@intel.com>,
        Mustafa Ismail <mustafa.ismail@intel.com>,
        Mark Brown <broonie@kernel.org>, linux-rdma@vger.kernel.org,
        linux-kernel@vger.kernel.org, target-devel@vger.kernel.org
From: Sagi Grimberg <sagi@grimberg.me>
Message-ID: <5489f4ef-02fb-5207-6261-c08ee805acae@grimberg.me>
Date: Mon, 21 Nov 2016 14:33:02 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101
 Thunderbird/45.4.0
MIME-Version: 1.0
In-Reply-To: <2625189.HB0S3sfnY7@wuerfel>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


>>> diff --git a/drivers/infiniband/ulp/isert/ib_isert.c b/drivers/infiniband/ulp/isert/ib_isert.c
>>> index 6dd43f6..de80f56 100644
>>> --- a/drivers/infiniband/ulp/isert/ib_isert.c
>>> +++ b/drivers/infiniband/ulp/isert/ib_isert.c
>>> @@ -619,7 +619,7 @@
>>>       mutex_unlock(&isert_np->mutex);
>>>
>>>       isert_info("np %p: Allow accept_np to continue\n", isert_np);
>>> -     up(&isert_np->sem);
>>> +     complete(&isert_np->comp);
>>>  }
>>>
>>>  static void
>>> @@ -2311,7 +2311,7 @@ struct rdma_cm_id *
>>>               isert_err("Unable to allocate struct isert_np\n");
>>>               return -ENOMEM;
>>>       }
>>> -     sema_init(&isert_np->sem, 0);
>>> +     init_completion(&isert_np->comp);
>>
>> This is still racy, a connect event can complete just before we
>> init the completion and *will* get lost...
>>
>> This code started off with a waitqueue which exposes the same
>> problem, see:
>> 531b7bf4bd79 Target/iser: Fix iscsit_accept_np and rdma_cm racy flow
>>
>> So, still NAK from me...
>
> I don't see what you mean here. The code using a waitqueue had no
> counter but the completion does.

The problem here is that init_completion sets the counter to zero
and between this thread wakes up and until it initializes comp->done
we might have another connect event completing it and I fail to
see how this is handled correctly.