From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201])
	(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))
	(No client certificate requested)
	by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8C39C271FD
	for <netdev@vger.kernel.org>; Tue, 16 May 2023 21:50:11 +0000 (UTC)
Received: by smtp.kernel.org (Postfix) with ESMTPSA id C0371C433EF;
	Tue, 16 May 2023 21:50:10 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;
	s=k20201202; t=1684273811;
	bh=yKkl+O+uwemVUkRqo3YT8W36ra+vpuQRbPNcizoUogE=;
	h=Date:From:To:Cc:Subject:In-Reply-To:References:From;
	b=fVWIMxwdFdnveGr0Eu1f+wb2bNaPbs0KhmFzgzLq704feoxQL0vucOiJjQUONdpmh
	 dr5/MV75n/TuMO2OihaPfcn6cHE3Zg14Ap7UpvvBRVeMGp4CmsDRBcukl8yGM5TaKA
	 azfMmCrsroyXZ+oM6Tjw2puCtKmyBqgvdXnDdz9ssNWjBi5C8CFXHoHUXspB2u/30V
	 FCwN5x41wuOa42vanctEHH1taIIVqRcBkSC5wLJuTzAFCwc16RaNESgkKG+c+NxMTT
	 /9R4ylh9qWb8PHSXVoM2CfA/hGw41Eo2q1k4zeCbBJUKGsr7YaZUr9WjEamy3Vkujb
	 UrEvX4+wuO1qQ==
Date: Tue, 16 May 2023 14:50:10 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Vlad Buslov <vladbu@nvidia.com>
Cc: Peilin Ye <yepeilin.cs@gmail.com>, Jiri Pirko <jiri@resnulli.us>,
 "Daniel Borkmann" <daniel@iogearbox.net>, "David S. Miller"
 <davem@davemloft.net>, Eric Dumazet <edumazet@google.com>, Paolo Abeni
 <pabeni@redhat.com>, "Jamal Hadi Salim" <jhs@mojatatu.com>, Cong Wang
 <xiyou.wangcong@gmail.com>, "Peilin Ye" <peilin.ye@bytedance.com>, John
 Fastabend <john.fastabend@gmail.com>, Pedro Tammela
 <pctammela@mojatatu.com>, Hillf Danton <hdanton@sina.com>,
 <netdev@vger.kernel.org>, <linux-kernel@vger.kernel.org>, Cong Wang
 <cong.wang@bytedance.com>
Subject: Re: [PATCH net 6/6] net/sched: qdisc_destroy() old ingress and
 clsact Qdiscs before grafting
Message-ID: <20230516145010.67a7fa67@kernel.org>
In-Reply-To: <87y1lojbus.fsf@nvidia.com>
References: <cover.1683326865.git.peilin.ye@bytedance.com>
	<e6c4681dd9205d702ae2e6124e20c6210520e76e.1683326865.git.peilin.ye@bytedance.com>
	<20230508183324.020f3ec7@kernel.org>
	<ZFv6Z7hssZ9snNAw@C02FL77VMD6R.googleapis.com>
	<20230510161559.2767b27a@kernel.org>
	<ZF1SqomxfPNfccrt@C02FL77VMD6R.googleapis.com>
	<20230511162023.3651970b@kernel.org>
	<ZF1+WTqIXfcPAD9Q@C02FL77VMD6R.googleapis.com>
	<ZF2EK3I2GDB5rZsM@C02FL77VMD6R.googleapis.com>
	<ZGK1+3CJOQucl+Jw@C02FL77VMD6R.googleapis.com>
	<20230516122205.6f198c3e@kernel.org>
	<87y1lojbus.fsf@nvidia.com>
Precedence: bulk
X-Mailing-List: netdev@vger.kernel.org
List-Id: <netdev.vger.kernel.org>
List-Subscribe: <mailto:netdev+subscribe@vger.kernel.org>
List-Unsubscribe: <mailto:netdev+unsubscribe@vger.kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit

On Tue, 16 May 2023 22:35:51 +0300 Vlad Buslov wrote:
> > Vlad, could you please clarify how you expect the unlocked filter
> > operations to work when the qdisc has global state?  
> 
> Jakub, I didn't account for per-net_device pointer usage by miniqp code
> hence this bug. I didn't comment on the fix because I was away from my
> PC last week but Peilin's approach seems reasonable to me. When Peilin
> brought up the issue initially I also tried to come up with some trick
> to contain the changes to miniqp code instead of changing core but
> couldn't think of anything workable due to the limitations already
> discussed in this thread. I'm open to explore alternative approaches to
> solving this issue, if that is what you suggest.

Given Peilin's investigation I think fix without changing core may
indeed be hard. I'm not sure if returning -EBUSY when qdisc refcnt
is elevated will be appreciated by the users, do we already have
similar behavior in other parts of TC?