From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <stable-bounces@dpdk.org>
Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124])
	by inbox.dpdk.org (Postfix) with ESMTP id 68BC4A0547
	for <public@inbox.dpdk.org>; Fri,  9 Apr 2021 16:56:27 +0200 (CEST)
Received: from [217.70.189.124] (localhost [127.0.0.1])
	by mails.dpdk.org (Postfix) with ESMTP id 5F4B014108F;
	Fri,  9 Apr 2021 16:56:27 +0200 (CEST)
Received: from mga18.intel.com (mga18.intel.com [134.134.136.126])
 by mails.dpdk.org (Postfix) with ESMTP id A12B94014D;
 Fri,  9 Apr 2021 16:56:25 +0200 (CEST)
IronPort-SDR: NeL50FeRQF8h2tTYjbnfv9/UBPB4sWlGFfGFXmJZtmVdrIBpf14UB1h0s8c6CirJyE3Y0BSuGM
 foKuKYy8awzQ==
X-IronPort-AV: E=McAfee;i="6000,8403,9949"; a="181309181"
X-IronPort-AV: E=Sophos;i="5.82,209,1613462400"; d="scan'208";a="181309181"
Received: from orsmga008.jf.intel.com ([10.7.209.65])
 by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384;
 09 Apr 2021 07:56:24 -0700
IronPort-SDR: 74duWh3BxU/dg751ERqSk/gpn1P8yQL5D1sUjTxK50Dqu8qvwfhOPDYe+pAVCFVuSRezpL/mup
 LVUm3Xr3L9Gg==
X-IronPort-AV: E=Sophos;i="5.82,209,1613462400"; d="scan'208";a="422759948"
Received: from fyigit-mobl1.ger.corp.intel.com (HELO [10.213.203.45])
 ([10.213.203.45])
 by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384;
 09 Apr 2021 07:56:22 -0700
From: Ferruh Yigit <ferruh.yigit@intel.com>
To: Elad Nachman <eladv6@gmail.com>, Igor Ryzhov <iryzhov@nfware.com>
Cc: stable@dpdk.org, Stephen Hemminger <stephen@networkplumber.org>,
 Dan Gora <dg@adax.com>, dev@dpdk.org
References: <20201126144613.4986-1-eladv6@gmail.com>
 <20210329143655.521750-1-ferruh.yigit@intel.com>
 <20210329143655.521750-3-ferruh.yigit@intel.com>
X-User: ferruhy
Message-ID: <b421b26d-0949-3277-2c00-5a7f287c2dd2@intel.com>
Date: Fri, 9 Apr 2021 15:56:19 +0100
MIME-Version: 1.0
In-Reply-To: <20210329143655.521750-3-ferruh.yigit@intel.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Subject: Re: [dpdk-stable] [PATCH v5 3/3] kni: fix kernel deadlock when
 using mlx devices
X-BeenThere: stable@dpdk.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: patches for DPDK stable branches <stable.dpdk.org>
List-Unsubscribe: <https://mails.dpdk.org/options/stable>,
 <mailto:stable-request@dpdk.org?subject=unsubscribe>
List-Archive: <http://mails.dpdk.org/archives/stable/>
List-Post: <mailto:stable@dpdk.org>
List-Help: <mailto:stable-request@dpdk.org?subject=help>
List-Subscribe: <https://mails.dpdk.org/listinfo/stable>,
 <mailto:stable-request@dpdk.org?subject=subscribe>
Errors-To: stable-bounces@dpdk.org
Sender: "stable" <stable-bounces@dpdk.org>

On 3/29/2021 3:36 PM, Ferruh Yigit wrote:
> KNI runs userspace callback with rtnl lock held, this is not working
> fine with some devices that needs to interact with kernel interface in
> the callback, like Mellanox devices.
> 
> The solution is releasing the rtnl lock before calling the userspace
> callback. But it requires two consideration:
> 
> 1. The rtnl lock needs to released before 'kni->sync_lock', otherwise it
>     causes deadlock with multiple KNI devices, please check below the A.
>     for the details of the deadlock condition.
> 
> 2. When rtnl lock is released for interface down event, it cause a
>     regression and deadlock, so can't release the rtnl lock for interface
>     down event, please check below B. for the details.
> 
> As a solution, interface down event is handled asynchronously and for
> all other events rtnl lock is released before processing the callback.
> 
> A. KNI sync lock is being locked while rtnl is held.
> If two threads are calling kni_net_process_request() ,
> then the first one will take the sync lock, release rtnl lock then sleep.
> The second thread will try to lock sync lock while holding rtnl.
> The first thread will wake, and try to lock rtnl, resulting in a
> deadlock.  The remedy is to release rtnl before locking the KNI sync
> lock.
> Since in between nothing is accessing Linux network-wise, no rtnl
> locking is needed.
> 
> B. There is a race condition in __dev_close_many() processing the
> close_list while the application terminates.
> It looks like if two KNI interfaces are terminating,
> and one releases the rtnl lock, the other takes it,
> updating the close_list in an unstable state,
> causing the close_list to become a circular linked list,
> hence list_for_each_entry() will endlessly loop inside
> __dev_close_many() .
> 
> To summarize:
> request != interface down : unlock rtnl, send request to user-space,
> wait for response, send the response error code to caller in user-space.
> 
> request == interface down: send request to user-space, return immediately
> with error code of 0 (success) to user-space.
> 
> Fixes: 3fc5ca2f6352 ("kni: initial import")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Elad Nachman <eladv6@gmail.com>
> ---
> Cc: Stephen Hemminger <stephen@networkplumber.org>
> Cc: Igor Ryzhov <iryzhov@nfware.com>
> Cc: Dan Gora <dg@adax.com>
> 

Hi Elad, Igor,

Can you please review/test this set when you have time?

Thanks,
ferruh