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 CEA121BB20
	for <netdev@vger.kernel.org>; Wed, 19 Jul 2023 20:51:51 +0000 (UTC)
Received: by smtp.kernel.org (Postfix) with ESMTPSA id DC22BC433C9;
	Wed, 19 Jul 2023 20:51:50 +0000 (UTC)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;
	s=k20201202; t=1689799911;
	bh=R5thK8MzXZwRF74d2FHPjnura0sN99c4ZZeDzrYKSwU=;
	h=Date:From:To:Cc:Subject:In-Reply-To:References:From;
	b=mp5F+HqNOqjXJTDdywXHW0z9pnTBc98MnAf7a8vhvVxpqq28oAHkeJRUXwIZQP6L8
	 DVQm0hDbNgrw0f8DhTUqr3U/4ib7oEnZ6/HgcZrCV18jEOq0FzjVeH8CWphtAjIEI4
	 DI6V3i9qTGAj8YC2iJ79sng2pfupjQcw2jYK6kXjH0h3FBTnequI7uJsiXWu07MuSJ
	 YsvDUj/eErevdSDanuKVwNB/LfVhDNvloJ7X9wRIjLYxWvOG9GhsbvrPdsrE9Vaz3v
	 WlZ4TB+kbPqpp/MOFoNb50WyKrK7Sxco6Cp+3lTuKLcXX7Hl9ZO0/upL53VElALfl2
	 /8Lf1Mvd0AmVA==
Date: Wed, 19 Jul 2023 13:51:50 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Alexander Lobakin <aleksander.lobakin@intel.com>
Cc: "David S. Miller" <davem@davemloft.net>, Eric Dumazet
 <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>, Maciej Fijalkowski
 <maciej.fijalkowski@intel.com>, Larysa Zaremba <larysa.zaremba@intel.com>,
 Yunsheng Lin <linyunsheng@huawei.com>, Alexander Duyck
 <alexanderduyck@fb.com>, Jesper Dangaard Brouer <hawk@kernel.org>, "Ilias
 Apalodimas" <ilias.apalodimas@linaro.org>, <netdev@vger.kernel.org>,
 <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC net-next v2 7/7] net: skbuff: always try to recycle
 PP pages directly when in softirq
Message-ID: <20230719135150.4da2f0ff@kernel.org>
In-Reply-To: <d7cd1903-de0e-0fe3-eb15-0146b589c7b0@intel.com>
References: <20230714170853.866018-1-aleksander.lobakin@intel.com>
	<20230714170853.866018-10-aleksander.lobakin@intel.com>
	<20230718174042.67c02449@kernel.org>
	<d7cd1903-de0e-0fe3-eb15-0146b589c7b0@intel.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 Wed, 19 Jul 2023 18:34:46 +0200 Alexander Lobakin wrote:
> > What if we got here from netpoll? napi budget was 0, so napi_safe is
> > false, but in_softirq() can be true or false.  
> 
> If we're on the same CPU where the NAPI would run and in the same
> context, i.e. softirq, in which the NAPI would run, what is the problem?
> If there really is a good one, I can handle it here.

#define SOFTIRQ_BITS		8
#define SOFTIRQ_MASK		(__IRQ_MASK(SOFTIRQ_BITS) << SOFTIRQ_SHIFT)
# define softirq_count()	(preempt_count() & SOFTIRQ_MASK)
#define in_softirq()		(softirq_count())

I don't know what else to add beyond that and the earlier explanation.

AFAIK pages as allocated by page pool do not benefit from the usual
KASAN / KMSAN checkers, so if we were to double-recycle a page once
a day because of a netcons race - it's going to be a month long debug
for those of us using Linux in production.